The spectral and laser characteristics of two anti-reflection (AR) coated Cr:ZnSe single crystals 3 mm and 5 mm long were investigated under ~1.7 μm laser diode pumping. The crystals were assembled in a copper holder actively cooled by circulating water. Room temperature absorption and fluorescence spectra were measured, together with the fluorescence lifetime of Cr2+ ions were measured. The influence of the pump pulse durations on the output laser power was investigated. The mean output power of ~2.7 W in CW mode at the wavelength of ~2.4 μm (~24% slope efficiency) was obtained with the 5 mm thick AR coated sample. In this case the M2 beam parameter of ~1.1±0.1 and the beam waist diameter of ~42±4 μm which corresponds to the maximum (in the beam waist) laser power density of ~200 kW/cm2. Furthermore, using a MgF2 birefringent plate, the laser output was tuned from ~2.05 μm up to ~2.65 μm with a spectral linewidth of ~5-10 nm and a Gaussian beam profile. The mean laser output power in the broad mid-infrared range of ~2.1-2.52 μm exceeded 1 W, which corresponds to a power density of at least ~73.5 kW/cm2.
In this work the results of research of an optimal concentration ratio of Cr2+ and Fe2+ co-doped active ions for more efficient Cr2+ → Fe2+ ions energy transfer in a chosen Zn1-xMnxSe (x ≈ 0.15) host material are presented. Three cryogenically cooled Cr2+,Fe2+:Zn1-xMnxSe (x ≈ 0.15) single crystals with the same thickness of ~2.7 mm and with different doping ratios of Cr2+ and Fe2+ ions of ~1:1, ~2:1, and ∼3:1 were investigated under Q-switched Er:YLF laser excitation (wavelength: ∼1.73 μm, pulse energy: ∼10 mJ, pulse duration: ∼150 ns). The temperature dependence of the absorption and fluorescence spectra, the fluorescence decay time as well as the laser output characteristics were measured. The Fe2+ ions maximum laser output of ~50 μJ at the wavelength range of ~4.25-4.42 μm was obtained with the crystal sample for which the active ions ratio was ~2:1. A further increase of the chromium ions amount (Cr2+:Fe2+ ≈ 3:1) led to worse results. Using appropriate resonator cavity mirrors, the samples were also able to generate the ~2.35-2.45 μm laser radiation from Cr2+ ions. The laser output beam spatial profiles were close to Gaussian in all cases. In summary, an optimized compact source of mid-infrared ~4.25-4.42 μm (Fe2+) and ~2.35-2.45 μm (Cr2+) of Cr,Fe:Zn1-xMnxSe (x ≈ 0.15) crystal pumped via Cr2+ ions by the ~1.73 μm radiation is described.
The spectroscopic and laser characteristics of optically polished Cr:ZnSe single crystals in four different lengths of 2, 3, 5, and 10 mm were investigated when pumping with a laser diode generating radiation at the wavelength of ~1.69 μm. The optimization from the point of laser efficiency was done in dependence on the crystal samples active length, effect of antireflection (AR) coatings, pumping pulse duration, and repetition rate. As a result, a 3 mm thick anti-reflection coated Cr:ZnSe crystal pumped by a laser diode with a pulse length of 20 ms and repetition rate of 10 Hz was chosen as the optimal. Using a 0.8 mm thick MgF2 birefringent filter the laser oscillations were continuously tunable from 2.1 μm up to 2.7 μm with the narrow spectral linewidth of ~5 nm and Gaussian beam profile. Maximum mean output power of ~0.35 W and maximum optical-to-optical slope efficiency of ~39% was obtained for 3 mm thick AR-coated sample which was ~28% and ~10% higher than that for uncoated sample of the same thickness, respectively. Continuously tunable laser oscillation wavelength was measured in the range of ∼2.1-2.7 µm with the mean output power of P ≥ 150 mW within a ∼5 nm linewidth. The absorption and fluorescence spectra as well as fluorescence lifetime were also measured. The Cr2+ fluorescence lifetime of ∼7.2 µs measured for the 1 ns pulse excitation at room temperature (RT) was constant within the whole absorption band of 1.35–2.25 µm.
The cryogenically cooled Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.4) single crystal with the thickness of ~3.6 mm was investigated under two different excitation wavelengths of the Q-switched Er:YAG laser (λ ≈ 2.94 μm, Eout ≈ 50 mJ) and by the gain-switched Fe:ZnSe laser (λ ≈ 4.05 μm, Eout ≈ 9 mJ). Because of relatively low Fe2+ ions concentration, the absorption coefficients at 78 K and 300 K ranged between 3 cm-1 and 2 cm-1 for both excitation wavelengths used. Absorption and fluorescence spectra, fluorescence lifetime as well as laser output characteristics were measured at low temperatures (78–180 K). The Cr,Fe:Zn1-xMgxSe (x ≈ 0.4) laser system was able to generate laser radiation at ~5 μm at liquid nitrogen (LN2) temperature of 78 K under both ~2.94 μm and ~4.05 μm laser excitation. The laser oscillation wavelength was shifted up to ~5 μm compared with a typical Fe:ZnSe output (~4.0–4.1 μm at LN2 temperature) due to the high amount of magnesium in the host material. Moreover, the oscillation wavelength was shifted even farther by increasing temperature of the active medium. The laser output energy was ~1.34 mJ and ~0.14 mJ for the ~2.94 μm and ~4.05 μm laser excitation, respectively. The beam profile structure was approximately fundamental for both excitation wavelengths used. The results present a novel mid-infrared 4.7–5.1 μm coherent laser source based on cubic AIIBVI matrix using direct excitation at wavelengths of ~2.94 μm or ~4.05 μm.
Two different mid-infrared (mid-IR) crystalline laser active media of Zn1-xMnxSe and Zn1-xMgxSe with similar manganese or magnesium ions amount of x ≈ 0.3 co-doped by divalent chromium (Cr2+) and iron (Fe2+) ions were investigated at cryogenic temperatures and compared for different excitation wavelengths used. Both single crystals were synthesized by high pressure Bridgman method and their thickness were 2.6 mm and 5 mm, respectively. Crystals were investigated under three excitation wavelengths of the Q-switched Er3+:YLF laser at ~1.73 μm, Q-switched Er3+:YAG laser at ~2.94 μm, and the gain-switched Fe2+:ZnSe laser operated at liquid nitrogen temperature of 78 K at a wavelength of ~4.05 μm. Spectroscopic and laser output characteristics were measured: absorption and fluorescence spectra, laser output pulse duration, mean output energy, and laser oscillation spectra. Both laser systems were able to generate radiation by Cr2+ or by Fe2+ ions under direct excitation, or by Fe2+ ions via the Cr2+ → Fe2+ energy transfer depending on the excitation wavelength and the output coupler conditions. Fe2+ ions in Cr2+,Fe2+:Zn1-xMnxSe and Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.3) laser systems at 78 K pumped by Er3+:YLF laser radiation at ~1.73 μm via the energy transfer mechanism generated laser radiation at the wavelengths of ~4.4 μm and ~4.8 μm at 78 K, respectively. Obtained results have shown a possibility of developing novel coherent laser systems in mid-IR region (~2.3 – 2.5 μm and ~4.4 – 4.9 μm) based on AIIBVI matrices. Thus, possibility to excite the Fe2+ active ions in both samples directly by ~2.94 μm as well as ~4.05 μm radiation or eventually in a compact way through the Cr2+ → Fe2+ ions energy transfer-based mechanism by ~1.73 μm radiation was demonstrated.
Two novel cryogenically cooled non-cubic wurtzite structure Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.2 and x ≈ 0.3) single crystals co-doped with Cr2+ and Fe2+ ions with thickness of 2.5 and 5 mm, respectively, were investigated under two excitation wavelengths of the Q-switched Er3+:YLF (λ ≈ 1.73 μm) and Er3+:YAG (λ ≈ 2.94 μm) lasers. Absorption and fluorescence spectra, fluorescence lifetimes as well as laser output characteristics for both Cr2+ and Fe2+ doping ions were measured at 78 K. Both Cr2+,Fe2+:Zn1-xMgxSe laser systems were able to generate radiation from Cr2+ as well as Fe2+ active ions depending on appropriate pumping wavelength and a set of laser cavity mirrors. Moreover, Fe2+ ions mid-IR lasing using the Cr2+ → Fe2+ ions energy transfer at ~4.57 μm and ~4.8 μm for magnesium content of x ≈ 0.2 and x ≈ 0.3, respectively were realized for ~1.73 μm Q-switched Er3+:YLF laser pumping. The results present an opportunity to develop novel mid-IR 4.4 – 4.9 μm coherent laser sources based on non-cubic AIIBVI matrices using direct Fe2+ ions pumping at ~2.94 μm as well as excitation via co-doped Cr2+ ions at ~1.73 μm.
New laser applications as medicine treatment, air pollutants measurement, free-space communications, target illumination, and industrial technologies require laser radiation in the mid-infrared region of 4–6 μm where Fe2+-based lasers can generate. Pumping of Fe2+-doped active material is usually provided by sources generating near 3 μm (as YAG:Er, Er-fiber, or ZnSe:Cr) fitting the Fe2+ absorption maximum. Other promising pumping way is the energy transfer from Cr2+ to Fe2+ in co-doped materials. This energy transfer process in gain-switched operation under 200 ns, 1.73 μm pulse excitation was reported recently. In this paper we would like to present 1 ms, 10 Hz laser operation of the Zn1-xMnxSe:Fe2+,Cr2+ (x = 0.3) crystal within the 78–110 K temperature range under 1.94 μm commercial Tm:fiber laser pumping. The active crystal was placed in the cryostat and the cavity was formed by a curved dichroic pumping mirror and a curved output coupler. The slope efficiency of 1 % was achieved for 1.94 μm pumping at 78 K. The central laser output wavelength at 78 K was ~4.45 μm and the output spectrum temperature shift was about 2 nm/K. Furthermore, tunability range over 300 nm (4.35–4.67 μm) obtained at 78 K using intracavity tuning element. The results will be compared to an analogous Zn1-xMnxSe:Fe2+ (x = 0.3) crystal in a gain-switched mode under Q-switched YAG:Er3+ 2.94 μm laser pumping. Moreover, laser generation of crystals with different Mn concentration and CW generation will be also presented.
Iron doped II-VI binary and ternary semiconductor materials are developed for mid-infrared (mid-IR) laser applications and some of them (ZnSe, ZnMnSe, ZnMgSe, CdMnTe) were already proven as laser active materials. In this article, the spectroscopic and laser properties of novel Fe2+ doped Zn1-xMnxTe (x ≈ 0.3) active material synthesized using Bridgman technique is presented. This active material was pumped by an Er:YAG laser at ~3 μm as well as Fe:ZnSe laser at 4.1 μm and has demonstrated various spectroscopic and laser output characteristics within the temperature range from 78 up to 300 K. At ~3 μm pumping, the central oscillation wavelength was ~4.8 μm at 78 K and shifted to 5.15 μm at 160 K. At 4.1 μm pumping, the central oscillation wavelength was red-shifted to ~4.9 μm at 78 K and shifted to 5.25 μm at 160 K. The output energy at 10 μJ level was achieved. These results present a great potential of the Fe2+:Zn1-xMnxTe (x ≈ 0.3) crystal for mid-IR laser radiation generation.
We present temperature influence (from 78 to 300,K) on tuning and laser properties of thulium doped solid solution CaF2-SrF2 crystal (Tm:CaF2SrF2). The sample was 8.5 mm thick Tm:CaF2SrF2 block cut and face polished parallel to growing axis without any AR coating. The composition of sample was 60 mol% CaF2, 38 mol% SrF2 doped with 2 mol% TmF3. The sample was mounted in temperature controlled copper holder of the liquid nitrogen cryostat. The 148mm long semi-hemispherical laser resonator consisted of flat pumping mirror (HR @ 1.80 - 2.10 μ m, HT @ 0.78 μm) placed inside cryostat, and curved output coupler (r=150mm, R = 98:0% @ 2 μm) placed outside. For longitudinal pumping a fiber coupled laser diode was used. The diode was operating in the pulse mode (10 ms pulse length, 10 Hz repetition rate) at wavelength 763 nm. The 2mm thick MgF2 birefringent filter was placed at Brewster angle inside the resonator for laser wavelength tuning. With decreasing temperature the output oscillation wavelength shifted to shorter wavelength and range of tunability decreased from 117nm at 300K to 89nm at 100K following the fluorescence spectrum narrowing. The overall tunability was from 1795nm at 79K to 1944nm at 300 K. The highest output pulse energy 6.8mJ with slope efficiency 10% was obtained at 1814nm for T = 78 K. The temperature of Tm:CaF2SrF2 was found to have significant influence on laser output wavelength and tunability.
The free-running and passive Q-switched laser properties of Er,La:SrF2-CaF2 crystal, that is appropriate for generation at 2.74 μm, are presented. The sample of Er,La:SrF2-CaF2 (composition 4 wt.% of ErF3, 12 wt.% of LaF3, 77 wt.% of CaF2, and 7 wt.% of SrF2, thickness 8.2 mm) had plan-parallel polished faces without anti-reflection coatings. The excitation of Er,La:SrF2-CaF2 was carried out by a 975 nm laser diode radiation in pulsed (pulse duration 1 ms, repetition rate 10 Hz) and CW mode. Laser resonator was hemispherical, 10 mm or 45 mm in length with flat pumping mirror (HR @ 2.7 μm) and spherical output coupler (r = 50 mm, R = 97.5 % or R = 95 % @ 2.5 - 2.8 μm). For CW mode of operation of Er,La:SrF2-CaF2 the highest obtained slope efficiency was 20.2 %. The maximum output power 0.35 W was achieved in this case. With semiconductor saturable absorber (SESAM) in laser resonator the shortest pulse duration of 33.4 ns with repetition rate 50 kHz was obtained. The maximal pulse energy 5.4 μJ with peak power 122 W was reached for 44.2 ns pulse duration. Since the emitted laser wavelength 2.74 μm is relatively close to absorption peak of water located at 3 μm, one of the Er,La:SrF2-CaF2 laser possible usage should be in medicine and spectroscopy.
The interest in the development of coherent mid-infrared radiation sources is caused by its potential application in medicine, spectroscopy, laser remote sensing of the atmosphere, metrology, and in many other fields of interest. This study presents temperature dependence of spectral properties of Cr:ZnSe laser active medium in range of 78-380 K. The temperature influence on the absorption, fluorescence and oscillation spectra were investigated in detail. While heating the Cr:ZnSe crystal from 78K to 380 K, the absorption peak maximum has shifted for 65nm toward a shorter wavelength from 1813nm to 1748nm together with the absorption spectrum broadening from 262nm to 373nm and decreasing the absorption coefficient. The FWHM of the fluorescence spectrum was broadened from 280nm (2030-2310 nm) to 488nm (1896-2384 nm) when the temperature of active medium was increasing. Pulsed laser operation from Cr:ZnSe active medium longitudinally pumped by an Er:YLF laser at 1735nm was investigated. The temperature dependence of Cr:ZnSe laser output energy and oscillation spectrum were studied. The highest output energy was 3.84mJ at 78K which together with the FWHM pulse duration of μ200 s corresponds to the power of 19mW. The laser radiation emission was observed at three wavelength bands which intensity was changing during the increase of crystal temperature. However, the oscillation band around wavelength of ~2360nm occurred for all measured temperatures. As a result, by cooling the system, the wavelength of maximum absorption is being shifted to the longer wavelengths as well as the wavelength of maximum fluorescence spectrum intensity.
Room temperature lasing of a set of Cd1-xMnxTe solid-solution crystals doped with Fe2+ ions was obtained under optical pumping by 4.1 μm liquid nitrogen cooled Fe2+:ZnSe laser. Oscillation wavelength maxima were found to increase linearly with Mn content x increase at a rate of about 60 nm per each 10 % of Mn content in the sample. The central oscillation wavelength as high as 5940 nm was obtained for sample with the highest Mn content (x = 0.76). The output energy was found to decrease for samples with higher Mn content due to very strong nonradiative fluorescence quenching.
The goal of this study was the investigation of temperature-dependent spectroscopic and laser properties of novel Fe:ZnMnSe crystal with high manganese (Mn) content of 0.4. The fluorescence spectrum at 78 K is broad covering the region from 4000 to 5500 nm. In comparison with a Fe:ZnSe crystal, the fluorescence maximum shift of ~600 nm towards the mid-IR region can be observed. With the increasing temperature, the fluorescence spectrum is getting generally broader together with the maximum shift towards the mid-IR spectral region. The central laser oscillation wavelengths were increasing with temperature from 5450 nm at 78 K up to 5800 nm at 300 K. The output energies were decreasing from 2 mJ at 78 K to 0.1 mJ at 300 K. To our best knowledge, these are the longest oscillation wavelengths generated using a ZnSe-based crystal under Er:YAG laser excitation.
The spectroscopy properties and lasing of diode pumped Tm-doped strontium molybdate SrMoO4 single crystal were investigated at room temperature. The Tm:SrMoO4 crystal was grown by modified Stepanov method (2 wt.% of TmNbO4 in the melt). The tested Tm:SrMoO4 sample was cut from the grown crystal boule perpendicularly to growth direction 100. For spectroscopy and laser experiments 4.2mm thick plane-parallel face-polished plate (without AR coatings) was used. A fiber-coupled laser diode operating at wavelength 793nm was used for longitudinal Tm:SrMoO4 pumping which corresponds to 3H4 level excitation. Fluorescence spectra measurement showed strong emission in vicinity of 1.8 μm (3F4 → 3H6 transition), and also significant emission close to wavelengths 1.45 μm (3H4 → 3F4 transition) and 2.3 μm (3H4 → 3H5 transition). The lasing was successfully reached for all these three transitions and output characteristics were measured. The pumping laser diode was operating in the pulsed regime with a low duty cycle. The 145mm long semi-hemispherical laser resonator consisted of flat pumping mirror (HT @ 0.79 μm) and curved (r = 150mm) output coupler. For each lasing transition the particular set of resonator mirrors was used to reach high reflexivity of pumping mirror and output coupler transmission 0.5% at laser operation wavelength. The obtained laser emission wavelengths were 1.95 μm, 1.45 & 1.49 μm, and 2.30 μm. In spite of low laser slope efficiency in respect to absorbed pumping power (0.45% for 3H4 → 3F4 transition, 0.50% for 3F4 → 3H6 transition and 0.83% for 3H4 → 3H5 transition), results obtained are promising for further development of diode-pumped laser at 2.3 μm spectral region.
Chromium ions Cr2+ are known to have good fluorescence properties in the mid-infrared spectral region around the
wavelength of 2.5 μm. The aim of this study was the investigation of new laser crystal materials – Zn0.95Mn0.05Se,
Zn0.70Mn 0.30Se, and Zn0.75Mg0.25Se doped by Cr2+ ions and comparison of their spectral and laser characteristics.
The spectroscopic parameters as absorption and fluorescence spectra as well as lifetimes were measured. As optical
pumping the laser diode generating radiation at the wavelength of 1.69 μm (pulse repetition rate 10 Hz, pulse width
2 ms) was used. The longitudinal-pumped resonator was hemispherical with an output coupler radius of curvature
150 mm. The laser emission spectra were investigated and the highest intensity of emitted radiation was achieved at
wavelengths 2451 nm, 2469 nm, and 2470 nm from the Cr:Zn0.95Mn0.05Se, Cr:Zn0.70Mn0.30Se, and Cr:Zn0.75Mg0.25Se laser
systems, respectively. The input-output characteristics of laser systems were measured; the maximum output peak power
177 mW was obtained for Cr:Zn0.95Mn0.05Se laser system with slope efficiency of 6.3 % with respect to absorbed peak
power. The output peak power as well as output beam spatial structure were stable during measurements. For the
selection of the lasing wavelength, the single 1.5 mm thick quartz plate was placed at the Brewster angle inside
the optical resonator between the output coupler and laser active medium. This element provided the tuning in
the wavelength range 2290–2578 nm, 2353–2543 nm, and 2420–2551 nm for Cr:Zn0.95Mn0.05Se, Cr:Zn0.70Mn0.30Se, and
Cr:Zn0.75Mg0.25Se, respectively. The obtained spectral FWHM linewidth of the individual output radiation was ~ 10 nm.
A comparison with previously measured Cr:ZnSe laser system was added in the end
In this work the temperature dependence of spectroscopic and laser properties of new ac-
tive medium Tm:SBN (Strontium-Barium Niobate, SrxBa1−xNb2O6, x = 0.61). The tested sample of Tm:SBN
(2 wt. % of Tm2O3) appropriate for generation of laser radiation at 1.88 μm had plan-parallel polished faces
without anti-reflection (thickness 6.65 mm). During spectroscopy and laser experiments the Tm:SBN was at-
tached to temperature-controlled copper holder and was placed in a vacuum chamber. The transmission and
emission spectra of Tm:SBN and the fluorescence decay time were measured depending on temperature range
80 - 350 K. The fluorescence decay time was measured to be 3.5 ms and 2.8 ms at 80 and 350 K, respectively.
Longitudinal excitation of Tm:SBN was carried out by a fibre-coupled laser diode (pulse duration 10 ms, rep-
etition rate 10 Hz, pump wavelength 793 nm). The laser resonator was hemispherical, 146 mm long, with flat
pumping mirror (HR @1.8 - 2.1 μm) and spherical output coupler (r = 150 mm, R = 97.5 % @1.8 - 2.1 μm).
The Tm:SBN laser properties were investigated at temperature range 80 - 300 K. The highest slope efficiency
with respect to absorbed pumped power was 3 % at 80 K. The maximum output peak amplitude power was
0.12 W at 80 K, i.e. 3.2 times higher than it was measured at 200 K. Tunability of laser wavelength at 80 K
in the range of 1827 - 1962 nm was obtained by using SiO2 birefringent filter. At 300 K, wavelength tunability
reached 1859 - 1970 nm. Thus, the new Tm:SBN crystal can be an useful laser material in the region of 2 μm.
Fe2+:Cd1-xMnxTe solid solution spectroscopic and lasing properties depending on temperature and Mn concentration x were investigated. A set of Fe2+:Cd1-xMnxTe crystals with different concentration of Mn (x = 0.1, 0.52, 0.68, and 0.78) was synthesized using Bridgeman technique with the Fe2+ ions doping (c ~ 1017 cm-3) during the synthesis process. The absorption spectra are broad covering the range from 2700 to 6000 nm with the maximum around 3500 nm. The fluorescence spectra are also broad ranging from 3500 nm to 7000 nm. The Fe2+:Cd1-xMnxTe laser oscillations at 77 K under short pulse (~200 ns) Fe:ZnSe cryogenically-cooled 4080 nm laser pumping and under long pulse (~150 us) Dy3+:PbGa2S4 4330 nm pumping were achieved successfully. The output energy of ~3 μJ was achieved in both cases. The oscillation spectrum maxima at 77 K were ~4950 nm for x = 0.1; ~5130 nm for x= 0.52; and ~5300 nm for x=0.78.
The goal of this work was an investigation of the temperature influence (in range 77 - 300 K) on laser properties of Tm:SrF2-CaF2 solid-solution, which is suitable as a gain medium for generation of radiation at 1.8-2 μm. The tested Tm:SrF2-CaF2 sample (60 mol% CaF2, 38 mol% SrF2) was doped with 2 mol% of TmF3. The diameter of the grown boule was 10 mm. The sample was cut and optically polished parallel to growing axis. The polished sample thickness was 8.5 mm. It was fixed in temperature controlled cupreous holder, placed inside vacuum chamber of the liquid nitrogen cryostat. A fiber coupled laser diode, operating in pulsed regime (10 ms pulse length, 10 Hz repetition rate) at wavelength 764 nm, was used for longitudinal sample pumping. The 142mm long semi-hemispherical laser cavity consisted of at pumping mirror (HR @ 1:8 - 2:0 μm, HT @ 0.77 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 92% @ 1:8 - 2:0 μm. From the results it follows that the temperature of the active medium has a strong infkuence on laser slope efficiency. The highest slope efficiency (42% in respect to absorbed power), obtained for temperature 77 K, was more than five times higher than slope efficiency for 300 K. The threshold decreased twice with the temperature lowering from 300 to 77 K. Laser output power amplitude 5.5W at wavelength 1856nm was reached for absorbed power 15.8W at 77 K.
We report on Pr:SrF2 single crystal laser operation at 639nm wavelength under blue laser diode pumping. The laser system was operated in the pulsed regime at 100 Hz repetition rate and 2 ms pulse duration. Using 3.5W InGaN laser diode as a pump source, 6mW of the mean output power at 639nm was extracted from the Pr:SrF2 sample. The corresponding slope efficiency related to the absorbed mean power was 16.4 %.
Fe:Zn(1-x)Mn(x)Se solid solution spectroscopic and laser properties were investigated in the temperature range 80- 290 K. Two novel samples with different zinc - manganese (Zn–Mn) ratio described by the Mn content x (0.1 or 0.2) were used and the results were compared to the known Fe:ZnSe crystal. The samples had a broad absorption spectra with the maximum around 3 μm and therefore an Er:YAG laser (2.94 μm, 10 mJ, 120 ns) was used as a pump radiation source. The Fe:ZnMnSe fluorescence spectra are generally broad in the range 3.5 – 5.5 μm. In the case of Fe:ZnMnSe x = 0.1, the fluorescence spectrum at 290 K is ranging from 3.5 to 5.5 μm. Lowering the temperature down to 80 K lead to the spectral narrowing mainly in the mid-IR part, but the fluorescence is still up to 5 μm at 80 K. In the case of Fe:ZnMnSe x = 0.2 the fluorescence is shifted towards mid-IR up to 5.2 μm even at 80 K. The fluorescence lifetime decreases from tens of us at 80 K down to 1 us at 240 K. The laser oscillations were successfully achieved with both novel Fe:ZnMnSe crystals in the temperature range 80- 290 K. In the case of x = 0.1, the central wavelength was ~4.2 μm at 80 K and the temperature increase up to 290 K led to almost linear increase of the wavelength up to ~4.75 μm. The tendency was similar in the case of Fe:ZnMnSe x = 0.2: the output wavelength increased from ~4.3 μm up to ~4.8 μm with the temperature increase from 80 to 290 K. The laser spectral linewidth was about 300 nm. In comparison with the Fe:ZnSe crystal, the laser output wavelength shift toward mid-IR region without any spectrally tunable element in the laser cavity can be clearly observed.
On the basis of our previous Dy3+:PbGa2S4 laser study, laser output wavelength temporal evolution as well as tuning possibilities in the range 4.3–4.7 μm were investigated. Active crystal was pumped by a fiber-coupled Brightlase Ultra- 50 diode laser (1.7 μm, max. power 7.5 W). Laser resonator was formed by flat dichroic pumping mirror (T = 70%@1.7 μm, R~100% @ 3.5 - 5 μm) and a concave (r = 200 mm) output coupler with R~99% @ 3.5 – 5 μm. The laser output wavelength dependence on the pump pulse duration and its evolution during the pulse was investigated first without any spectrally-selective element in the cavity. At pump pulse duration of 1 ms, generation just near Dy3+ fluorescence maximum of 4.35 μm has been observed. Prolongation of the pulse up to 5 ms led to similar lasing at 4.35 μm in the first millisecond, followed by simultaneous generation at 4.35 and 4.38 μm in the next millisecond, and further lasing at 4.6 μm till the end of the pump pulse. Increase of pump pulse duration up to 10 ms led to similar oscillation pulse development followed by generation at 4.6 μm only. Furthermore, output wavelength tuning using MgF2 birefringent filter as a cavity spectral selective element was investigated under 10 ms pumping. Almost continuous tuning without any significant dip has been observed within spectral range from 4.3 up to 4.7 μm. Due to practically closed cavity mean output power in the maximum of tuning curve was in the order of 400 μW.
The laser and spectroscopic properties of crystal Er,La:SrF2-CaF2 at temperature range 80 - 300 K, which is appropriate for generation of radiation around 2.7 um is presented. The sample of Er,La:SrF2-CaF2 (concentration Er(0.04), La(0.12):Ca(0.77)Sr(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:SrF2-CaF2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:SrF2-CaF2 together with the fluorescence decay time were measured in dependence on temperature. The excitation of Er,La:SrF2-CaF2 was carried out by a laser diode radiation (pulse duration 5 ms, repetition rate 20 Hz, pump wavelength 973 nm). Laser resonator was hemispherical, 140 mm in length with at pumping mirror (HR @ 2.7 µm) and spherical output coupler (r = 150 mm, R = 95 % @ 2.5 - 2.8 µm). Tunability of laser at 80 K in range 2690 - 2765 nm was obtained using MgF2 birefringent filter. With decreasing temperature of sample the fluorescence lifetime of manifold 4I11/2 (upper laser level) became shorter and intensity of up-conversion radiation was increasing. The highest slope efficiency with respect to absorbed power was 2.3 % at 80 K. The maximum output of peak amplitude power was 0.3 W at 80 K, i.e. 1.5 times higher than measured this value at 300 K. The wavelength generated by Er,La:SrF2-CaF2 laser (2.7 µm) is relatively close to absorption peak of water (3 µm) and so, one of the possible usage should be in medicine and spectroscopy.
The goal of this work was an investigation of the temperature influence (in range from 80 up to 330 K) on the
laser properties of Er:CaF2 ceramics, which is suitable as a gain medium for generation of radiation at 2.7 μm.
The tested Er:CaF2 ceramics sample, prepared using a hot-forming technique, was doped with 5.5% of ErF3. The
sample was in the form of plane-parallel face-polished 5.8mm thick plate (without AR-coatings). It was mounted
in a temperature controlled cupreous holder, placed inside the vacuum chamber of the liquid nitrogen cryostat.
A fiber coupled laser diode, operating in pulsed regime (3 ms pulse length, 20 Hz repetition rate) at wavelength
968 nm, was used for Er:CaF2 sample pumping. The 145mm long semi-hemispherical laser resonator consisted
of a flat pumping mirror (HR @ 2.65 − 2.95 μm, HT @ 0.97 μm) and a curved (r = 150mm) output coupler
with a reflectivity of ∼ 97% @ 2.65 − 2.85 μm. From the results it follows that the temperature of the active
medium has a strong influence mainly on laser threshold (more than 8 times lower threshold power corresponded
to the temperature 80K in respect to 330 K). The highest slope efficiency (2.3% in respect to absorbed power),
obtained for the temperature 80 K, was more than twice higher than the slope efficiency for 330 K.
The aim of the presented work was to design and characterize bulk Fe:ZnSe and Fe:Zn(1-x)Mg(x)Se (Mg content
x = 0.19) lasers coherently pumped by electro-optically Q-switched Er:YSGG laser. This laser generated pumping
radiation at 2.79 μm with the maximum energy of 50 mJ in 80 ns long pulse with the repetition-rate of 1 Hz. The 25 mm
long optical resonator of Fe:ZnSe or Fe:ZnMgSe lasers was formed by a plan dichroic pumping mirror and a concave
output coupler (r = 200 mm) with reflectivity 88 % @ 4-5 μm. Both lasers were operated at room temperature. Measured
maximum output energy/slope efficiency in respect to the absorbed energy was ~ 3.8 mJ/42 % for the Fe:ZnSe laser and
~ 0.48 mJ/10 % for the Fe:ZnMgSe laser. The generated output pulse duration was 150 – 200 ns in both cases and the
output beam spatial profile was approximately gaussian. The Fe:ZnSe and Fe:ZnMgSe lasers output spectra line-width
was ~ 200 nm (FWHM) and their maxima were centered at 4.45 μm and 4.8 μm, respectively. The results were
compared to pumping the same crystals by a Q-switched Er:YAG laser in similar conditions.
Temperature dependence of spectroscopic characteristics as well as laser properties of the bulk Bridgman-grown Fe:ZnSe and Fe,Cr:Zn1-xMgxSe (x = 0.19, 0.38) active media were investigated under room and various cryogenic – liquid nitrogen - temperature . The pumping was provided by Er:YAG laser radiation at the wavelength of 2.94 μm, with energy 15 mJ in 110 ns Q-switched pulse or 200 mJ in 220 μs free-running pulse. The 55 mm long hemispherical resonator was formed by a dichroic pumping mirror (T = 92 % @ 2.94 μm and R = 100% @ 4.5 μm) and a concave output coupler (R = 95 % @ 4.5 μm, r = 200 mm). A strong dependence of generated output radiation parameters on temperature was observed for all samples.
The spectroscopic and laser properties of bulk Bridgman-grown Zn1-xMgxSe single crystals with the various concentrations of Mg (x=0.19; x=0.27; x=0.38) were investigated in the wide temperature range. The pumping was provided by a 2.94 μm Q-switched Er:YAG laser with a maximal energy of 15 mJ in 120 ns pulse, repetition rate 1 Hz. Q-switched operation was achieved by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the Er:YAG laser active medium. The pump radiation was directed into the Fe:ZnMgSe crystal placed inside the LN cooled dewar. The 55 mm long plane-concave cavity was formed by a dichroic pumping mirror (T = 92 % @ 2.94 μm and R = 100 % @ 4 - 5 μm) and a output coupler (R = 95 % @ 4.5 μm, r = 200 mm). The strong dependence of output pulse energy on temperature was observed for all samples. The maximum output Fe,Cr:Zn1- xMgxSe laser energy was 230 μJ and 180 μJ (for Mg concentration x=0.19 and x=0.38, respectively) for gain switched operation at 88 K. The central emission wavelength of ~ 4600 nm, ~ 4700 nm and ~ 4800 nm for Mg concentration x=0.19; x=0.27, and x=0.37, respectively at 88 K was obtained. The emission wavelength was found to increase up to ~ 4700 nm and ~ 4900 nm at 250 K for Mg concentration x=0.19 and x=0.38, respectively. This results show the possibility to obtain sufficiently longer oscillation wavelengths compared to previously studied Fe:ZnSe active medium especially at liquid nitrogen temperatures when pumping by free-running Er:YAG laser becomes possible. Fluorescence spectra and lifetimes of Fe2+ ions in different Zn1-xMgxSe crystals in the range from 250 K down to 80 K were also measured.
The Tm:CaF2 (4% of TmF3) and Tm:Ho:CaF2 (2% of TmF3, 0.3% of HoF3) ceramics, prepared using hot pressing, and hot formation technique had been used as an active medium of diode pumped mid-infrared tunable laser. A fibre (core diameter 400 μm, NA = 0.22) coupled laser diode (LIMO, HLU30F400-790) was used to longitudinal pumping. The laser diode was operating in the pulsed regime (6 ms pulse length, 10 Hz repetition rate). The duty-cycle 6% ensures a low thermal load even under the maximum diode pumping power amplitude 25W (ceramics samples were only air-cooled). The laser diode emission wavelength was 786 nm. The 80mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.85 − 2.15 μm, HT @ 0.78 μm) and a curved (r = 150mm) output coupler with a reflectivity of ∼ 98% @ 1.85 − 2.0 μm for Tm:CaF2 laser or ∼ 99.5% @ 2.0 − 2.15 μm for Ho:Tm:CaF2. Tuning of the laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle. Both samples offered broad and smooth tuning possibilities in mid-IR spectral range and the lasers were continuously tunable over ∼ 100 nm. The obtained Tm:CaF2 tunability ranged from 1892 to 1992nm (the maximum output energy 1.8mJ was reached at 1952nm for absorbed pumping energy 78 mJ). In case of Tm:Ho:CaF2 laser tunability from 2016 to 2111nm was reached (the maximum output energy 1.5mJ was reached at 2083nm for absorbed pumping energy 53 mJ). Both these material are good candidates for a future investigation of high energy, ultra-short, laser pulse generation.
The goal of this work was to design and investigate a Fe:ZnSe laser operating at room and cryogenic (down to liquid nitrogen) temperature. Pumping was provided by a Q-switched Er:YAG laser at the wavelength of 2.94 μm, the output energy 15 mJ, pulse duration 120 ns, and the repetition rate 1 Hz. Q-switched operation was achieved by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the Er:YAG laser active medium. The pump radiation was directed into the Fe:ZnSe crystal placed in the vacuum chamber cooled by liquid nitrogen. The resonator was formed by a dichroic pumping mirror (T = 78 % at 2.94 μm and R = 100 % at 4.5 μm), and a concave output coupler (R = 95 % at 4.5 μm, r = 500 mm). Fluorescence spectra and lifetime of the bulk Bridgman-grown Fe:ZnSe crystal in the range from room temperature down to liquid nitrogen temperature were measured as well as the output characteristics of the Fe:ZnSe laser. The shift of the generated spectral line maximum of ~ 400 nm towards the shorter wavelengths was found for the change of temperature from room to the liquid nitrogen. Also the increase of lifetime was measured from 300 ns at the room temperature up to 100 μs at the temperature of 130 K. Maximum of generated output radiation at 130 K was 150 μJ with the central emission wavelength of 4.1 μm. At the room temperature the central emission wavelength of 4.45 μm was measured with the spectral line-width of ~100 nm. The generated output energy was 1.3 mJ. The comparison of results obtained for Fe:ZnSe active material with the new bulk Fe,Cr:ZnMgSe crystal was also made. The results obtained for Fe:ZnSe active material were compared with the investigation of new bulk crystal Fe,Cr:ZnMgSe.
The aim of the presented work is to demonstrate operation of a Cr:ZnMgSe laser pumped by a Er:YLF laser. Laser output characteristics are compared with a Cr:ZnSe laser operated under similar conditions. Pumping 1.73 μm Er:YLF laser (Er:YLF rod 80 mm long, flashlamp-pumped) radiation was focused into the Cr:ZnMgSe or Cr:ZnSe active crystal (thickness 4.9 mm and 2.2 mm, respectively; absorption coeficient 4.5 and 10.9 cm-1 @ 1.73 μm, respectively). The active crystal was inserted into the stable non-selective optical resonator or into the resonator with a wavelength-selective element. The 65 mm long non-selective resonator was formed by a flat dichroic pumping mirror (HT @ 1.74 μm, HR @ 2.4 μm), and a concave output coupler (R = 82 % @ 2.4 μm, r = 500 mm). The maximal output pulse energy and efficiency with respect to the absorbed pumping energy were measured 5.8 mJ and 36 % for the Cr:ZnMgSe laser, and 10.2 mJ and 76 % for the Cr:ZnSe laser. Central emission wavelength was 2.46 μm and 2.4 μm for the Cr:ZnMgSe and Cr:ZnSe laser, respectively. The spectral line-width was about 55 nm in both cases. In the case of 80 mm long output wavelength selective resonator the MgF2 Lyot filter was inserted between the active crystal and the output coupler. Output wavelength tuning was obtained in the range 2.35 – 2.55 μm and 2.29 - 2.53 μm for the Cr:ZnMgSe and Cr:ZnSe laser, respectively. Maximum output energy was ~ 4 mJ in both cases.
The aim of presented study was an investigation of tunability of diode pumped laser based on hot-pressed
Yb:CaF2 ceramics. The tested Yb:CaF2 sample was in the form of 3.5mm thick plane-parallel face-polished
plate (without AR coatings). The Yb3+ concentration was 5.5 %. A fiber (core diameter 200 μm, NA= 0.22)
coupled laser diode (LIMO, HLU25F200-980) with emission at wavelength 976 nm, was used for longitudinal
Yb:CaF2 pumping. The laser diode was operating in the pulsed regime (4 ms pulse length, 20 Hz repetition
rate). The duty-cycle 8% ensured a low thermal load even under the maximum diode pumping power amplitude
10W (crystal sample was only air-cooled). This radiation was focused into the crystal (pumping beam waist
diameter ~ 170 μm). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror
(HR @ 1.01 − 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 98%
@ 1.01 − 1.09 μm. Tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm
thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and
the laser active medium. The extremely broad and smooth tuning was obtained. The laser was continuously
tunable over ~ 66nm (from 1015nm to 1081 nm) and the tuning band was mostly limited by free spectral range
of used birefringent filter. The tunability FWHM was 40 nm corresponding bandwidth 10 THz results in Fourier
limited gaussian pulse width ~ 40 fs (FWHM). The maximum output power amplitude 0.68W was obtained at
wavelength 1054nm for absorbed pump power amplitude 6W. The laser slope efficiency was 15%.
The aim of this work was the delivery investigation of 3 - 5 μm laser radiation by a hollow glass waveguide. The
waveguide was formed by a supporting fused silica glass capillary tube with a silver layer deposited on the inside wall.
As an inner dielectric material film, a cyclic olefin polymer (COP) was used. The primary parameters of the sample
investigated were the inner/outer diameter 700/850 μm and the length of up to 110 cm. As radiation sources, three lasers
generating in mid-infrared spectral region were designed and constructed. The flash-lamp-pumped Er:YAG laser
operated at 2.94 μm wavelength. The second system was 4.3 μm Dy:PbGa2S4 laser. Its coherent pumping was performed
by the flashlamp pumped Er:YLF laser generating at 1.73 μm wavelength. The third laser emitting at 4.45 μm was based
on Fe:ZnSe active medium pumped by electro-optically Q-switched Er:YAG laser radiation (2.94 μm). The study
presented describes a transfer capability of 3 - 5 μm radiation by COP/Ag hollow glass waveguide. The delivery
efficiency and spatial structure were investigated. The transmission measured reached 84 %, 58 %, and 64 % for
Er:YAG (2.94 μm), Dy:PbGa2S4 (4.3 μm), and Fe:ZnSe (4.45 μm) laser systems, respectively. The spatial beam
structure transferred was similar for all systems. The laser delivery system based on COP/Ag hollow glass waveguide
can be useful for some mid-infrared radiation applications.
The goal of this work was to design and investigate the gain switched new Fe,Cr:ZnMgSe laser operating at the room
temperature. The pumping was provided by the electro-optically Q-switched Er:YAG laser with the oscillation
wavelength of 2.937 μm which matching the absorption line of the Fe,Cr:ZnMgSe crystal. The Q-switched operation
was obtained by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the laser active medium.
The output radiation parameters were: the energy of 10 mJ, pulse duration of 120 ns, and repetition rate 1 Hz.
The pump radiation was directed into the Fe,Cr:ZnMgSe crystal placed inside the 16 mm long hemi-spherical cavity
formed by the dichroic pumping mirror (T = 86 % at 2.94 μm and R = 100% for 4 - 5 μm) and the output coupler with
the reflectance R = 95 % at 4 - 5 μm and radius of curvature r = 500 mm. The maximum output Fe,Cr:ZnMgSe laser
energy was 160 μJ corresponding the slope efficiency 4 % (with respect to absorbed energy). The generated radiation
wavelength was 4.8 μm with the linewidth of 100 nm (FWHM). The output beam spatial profile was approximately
Gaussian in both axes.
Laser tuning properties were investigated by the Lyot filter (MgF2 plate, 2 mm thick) inserted into the resonator
providing the tuning range from 4.5 to 4.9 μm. The results were compared with the Fe:ZnSe crystal operated at the same
conditions.
One of the promising active ions giving the possibility of laser radiation generation in 4 - 5 μm region is trivalent
dysprosium in lead thiogallate crystal. On the basis of our previous Dy3+:PbGa2S4 laser study, this work is showing a
several wavelengths generation possibility. The laser was working at the room temperature and it was in-band pumped
by the Er:YLF laser radiation with the wavelength 1.73 μm. The investigated crystal Dy3+:PbGa2S4 was synthesized
using Bridgman technique from the melt. Dimension of the sample was 16 mm long and 19 mm in diameter and the
nominal Dy3+ ion concentration was ~ 0.7 at. %. The laser operation was tested with three resonator configurations. The
first was the non-selective resonator with the length 41 mm. To perform the wavelength tuning, in the second case the
MgF2 Lyot filter was inserted under Brewster angle inside the resonator which length was 100 mm. In both these cases
the laser resonator was formed by the incoupling flat dichroic mirror with low reflectivity at pumping wavelength (T =
90%@1.73 μm) and high reflectivity (R~100%) within the 3.5 - 4.5 μm spectral range, and by an out-coupling concave
(r = 500 mm) mirror with reflectivity of 95 % or 98 % in the same region of wavelengths. For the third case the selective
mirrors supporting the 3.0 - 4.0 μm spectral region were chosen. The generation possibility on three lines 4 μm, 4.3 μm,
and 4.6 μm were found without continuous tuning between them.
The mid-infrared radiation generated by bulk Dy:PbGa2S4 laser working at room temperature was characterized and for
its delivery the special type of COP/Ag hollow waveguide was used. The optical pumping of Dy:PbGa2S4 laser was
performed by flashlamp pumped Er:YLF laser at 1.73 μm wavelength. The compact 60 mm long Dy:PbGa2S4 laser
oscillator worked in free-running mode with the repetition rate 1.5 Hz. The output energy was 5.1 mJ in 80 μs long pulse
at 4.3 μm wavelength. The spatial beam structure was close to the Gaussian shape.
The goal of the presented study was the preliminary investigation of the mid-infrared Dy:PbGa2S4 radiation delivery
possibility by the cyclic olefin polymer and silver coated hollow glass waveguide. The length of the waveguide was
103 cm and the inner diameter was 700 μm. The thickness of the polymer inner layer was calculated for the optimal
4 μm radiation transmission. Mid-infrared laser radiation was coupled into the waveguide by the CaF2 lens with the focal
length 55 mm. The characterization of delivered 4.3 μm radiation was provided. It was observed that the spatial structure
is changing essentially, which follows from the transmission principle of the hollow waveguide. As conclude the
delivery system for 4.3 μm mid-infrared Dy:PbGa2S4 laser radiation was investigated for the first time.
The aim of the presented project was comparison of two Fe:ZnSe lasers based on Fe:ZnSe bulk active crystals grown by
two different methods - Bridgman and floating zone. For pumping the Q-switched Er:YAG laser generating 15 mJ and
300 ns giant pulses was used. The highest Fe:ZnSe laser generated output energy was 1.2 - 1.3 mJ for both investigated
crystals, the pulse duration was 150 - 200 ns. The Fe:ZnSe laser threshold was reached at absorbed pumping energy of
~ 1 mJ. Tuning properties using intracavity CaF2 prism were also investigated and tuning range ~ 4 - 5 μm was observed
for both crystals.
A special type of Cyclic Olephin Polymer silver coated (COP/Ag) hollow waveguide was used for delivery of 4.45 μm
laser radiation. This mid-infrared radiation having major signification in special lidar or spectroscopy applications was
generated by new bulk Fe:ZnSe laser working at the room temperature in gain switched regime. The coherent pumping
of Fe:ZnSe laser was performed by electro-optically Q-switched Er:YAG laser which wavelength (2.94 μm) corresponds
to the maximum of Fe:ZnSe absorption peak. The Er:YAG laser energy and pulse-length used was 11 mJ and ~ 300 ns,
respectively. The generated Fe:ZnSe laser output energy was reached 1.1 mJ with the pulse-length 240 ns.
The aim of the presented project was to investigate the transmission possibility of 4.45 μm mid-infrared Fe:ZnSe
radiation by the COP/Ag hollow glass waveguide. The inner waveguide diameter was 700 μm and length 103 cm. Midinfrared
laser radiation was focused into the guidance protector by the CaF2 lens with the focal length 55 mm. After the
coupling Fe:ZnSe radiation optimization, the maximum transmission of radiation through the waveguide reached 64%.
The time evolution of the pulse was not changed by the delivery but the space structure is changing essentially. It follows
from the radiation transport principle of the hollow waveguide. The bent waveguide transmission was also investigated
and 60% was obtained. For the case of contact application the fused silica cap was performed. As conclude the compact
delivery system for 4.45 μm mid-infrared radiation with the short 240 ns pulse length and transmitted power density
0.57 MW/cm2 was successfully investigated and it can be used for the applications.
The goal of this work was to design and investigate a gain switched, at room temperature lasing Fe:ZnSe laser. The active medium was a bulk, by Bridgman-technique grown Fe:ZnSe sample with the thickness 3.4 mm. The pumping was provided by electro-optically Q-switched Er:YAG laser with the oscillation wavelength 2.937 μm matching the local maximum of the Fe:ZnSe absorption. The Er:YAG Q-switched operation was obtained by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the laser active medium. No additional intracavity polarizers were used. The maximum pumping pulse energy and length was 15 mJ, and ~300 ns, respectively. This pulse-length is close to room-temperature measured lifetime of Fe2+ ions in Fe:ZnSe crystal.
The pump radiation was directed into the Fe:ZnSe crystal which was placed inside the cavity formed by dichroic
pumping mirror (THR=92% at 2.94 μm and RHR~100% for 3.5-5.2 μm) and optimal output coupler with the reflectance ROC=90% at 4.5 μm, radius of curvature r = -200 mm. The maximum obtained output Fe:ZnSe laser energy was 1.2 mJ, the generated output pulse duration on the wavelength 4.5 μm was 65 ns (FWHM). The output pulse profile was approximately Gaussian. The crystal showed rather high uniformity of oscillation properties throughout its volume. For the case of tuning the CaF2 prism was implemented into the resonator. The tuning curve of generated Fe:ZnSe laser radiation covered the spectral range 3.9 - 4.7 μm.
Cr:ZnSe laser coherently longitudinally pumped with Tm:YAP microchip laser was realised.
The pumping laser consisted of Tm:YAP crystal (3x3 mm) with resonator mirrors deposited
directly on its faces (on rear face the dielectric layer with high reflectance for 1998 nm
wavelength and high transmittance for 790 nm pumping radiation wavelength; on output face
the dielectric layer with reflectance 97% at 1998 nm wavelength). The maximal output power
was 5.5 W and the generated radiation wavelength was 1998 nm. The main advantage of this
pumping was stable and still output without relaxation spikes (non-spiking).
The Tm:YAP laser radiation was collimated and focused by the set of two CaF2 lenses. The
pumping beam spot diameter inside the Cr:ZnSe crystal was 300 μm. The Cr:ZnSe laser
resonator consisted of flat rear mirror (HT at 1998 nm and HR at 2100 - 2900 nm) and curved
output coupler (r = -150 mm, R = 95% at 2100 - 2700 nm). The maximal output energy of
stable radiation was 4 mJ (pulse duration 10 ms, repetition rate 10 Hz). For wavelength tuning
the Lyott filter (quartz plate under Brewster angle) was placed between the Cr:ZnSe crystal
and output coupler. The generated radiation wavelength was continuously tunable from 2246
- 2650 nm.
The lead thiogallate (Dy:PbGa2S4) crystal doped with trivalent dysprosium ions was used as a laser active medium for
obtaining radiation in mid-IR spectral region. To prove in-band pumping, the Er:YAP laser generating 1.66 μm radiation
was used. This radiation was focused by CaF2 lens (f = 100 mm) on the investigated Dy:PbGa2S4 crystal placed inside
the resonator formed by an in-coupling flat-dichroic mirror with low reflectivity at pumping wavelength and with high
reflectivity within the 4-5 μm spectral range, and by an out-coupling concave mirror (500 mm curvature) with
reflectances of 86%, 88%, 89%, and 93% at 4325 nm. Three Dy:PbGa2S4 active crystals were investigated. The
Dy:PbGa2S4 laser was working at room temperature without any cooling. The maximal reached output energy was as
high as 275 μJ for the optimal mirror reflectance and the best Dy:PbGa2S4 crystal. The incident pumping energy was 132
mJ. The measured output radiation wavelength was 4332 nm with the spectral width of 62 nm. From the point of
efficiency it was recognized that the in-band pumping directly into 6H11/2 level results in decrease of lasing threshold and
increase of slope efficiency.
Fe:ZnSe is one of the most promising materials capable of generating broadly tunable laser radiation in the wavelength
range from 3.5 to 5 μm. The aim of the work was to test laser properties of the Bridgman-method-grown Fe2+:ZnSe
crystal activated through the synthesis process as an active medium coherently pumped with the Q-switched Er:YAG
laser whose oscillation wavelength (2937 nm) corresponds to the maximum of the Fe2+:ZnSe absorption spectrum. The
Er:YAG laser generated giant pulses with the duration 160 - 200 ns and energy 20 - 30 mJ. The repetition-rate was set
to be 1 Hz. The oscillation properties, such as the pulse length, energy, and generated beam spatial structure, of the
Bridgman-method-grown Fe2+:ZnSe crystal used as an active medium of Fe2+:ZnSe laser operated at room temperature
were investigated. The maximal obtained output energy of room temperature Fe2+:ZnSe laser was 580 μJ for the
absorbed energy of 5.3 mJ which corresponds to slope efficiency of 38%. The generated pulse waveform was found to
follow that of the pump one.
Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared
laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as
continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman
method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers
were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser
(generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped
Tm:YAP laser (generated wavelength 1980 nm).
In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the
Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active
Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The
Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm.
The generated radiation beam spatial structure was close to TEM00.
Stimulated Raman scattering (SRS) in BaWO4 crystal under 1.56 μm pumping was investigated. Several (up to
fourth) Stokes components were observed. Mid IR spectral range 2.75 µm and 3.7 μm radiation was obtained using
BaWO4 crystalline Raman shifter. Under 1.318 μm pumping 4.3 μm and 4.7 μm oscillations in low phonon
PbGa2S4:Dy3+ laser were obtained.
Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and
medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser.
The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.
The goal of our research was the construction of the laser emitting short pulses with high peak power in "eye-safe" region around wavelength 1.5 μm. We use Raman self-conversion of giant pulses at wavelength 1.3 μm in Nd3+-doped Raman active crystal SrMoO4 (diameter 4.4 mm, length 42 mm). Fundamental laser wavelength was obtained using this advanced solid-state medium Nd3+:SrMoO4, lasing at 1378.1 nm, and pumped at wavelength 752nm by free-running alexandrite laser. High-peak power required for efficient Raman conversion was reached by Q-switching of the Nd3+:SrMoO4 laser by V:YAG solid-state saturable absorber (initial transmission 93% @ 1380 nm). Specially designed resonator mirrors were used to ensure proper feed-back for Raman laser. The resonator pump mirror was concave with 0.5m curvature and with high transmission at 752nm and high reflectivity in the range from 1250nm to 1580 nm; the reflectivity of the output coupler was 3% @ 1380nm and 25% @ 1570 nm. Both mirrors have reflectivity around 1 μm as small as possible to prevent lasing at other Nd3+ lines. With the described laser system, simultaneous generation of wavelengths 1378.1nm and 1569.8nm was obtained. The single pulse output energy 0.8mJ at 1569.8nm was reached. The length of the generated pulse at this wavelength was measured to be 8.7 ns (FWHM). These values correspond with the peak power of 92 kW in eye-safe region.
Cr:ZnSe crystals grown by the Bridgeman technique from the melt in inert gas (argon) under pressure were
characterized and utilized as effective laser active material.
Large crystalline boules with a necessary concentration of Cr2+ ions 1019 cm-3, practically homogeneously distributed
throughout the crystal bulk (50 mm in diameter and up to 100 mm in length), were prepared. For the laser evaluation
the Cr:ZnSe samples in the form of 6 mm thick blocks were polished.
Cr:ZnSe laser was longitudinally coherently pumped either with flashlamp-pumped Er:YAP laser radiation (emission
wavelength 1658 nm) or with diode-pumped Tm:YAP laser radiation (emission wavelength 1980 nm).
In the first case, the Cr:ZnSe laser was pumped with radiation of Er:YAP laser working in free-running regime (pulse
length 200 &mgr;s, pulse energy 200 mJ, repetition rate 1 Hz). The maximal obtained Cr:ZnSe laser pulse energy was 14
mJ (slope-efficiency 73%). Using the dispersive prism inside the resonator, the output laser radiation was broadly
tunable from 2150 nm up to 2600 nm.
In the second case, the Cr:ZnSe laser was pumped with radiation of diode-pumped solid-state Tm:YAP laser working
in pulsed as well as continuous-wave regime, for which the maximal obtained Cr:ZnSe laser output power was 200
mW (slope-efficiency 67%). The output spectrum of generated radiation covered the range from 2100 nm to 2400
nm. The temporal profile and spatial structure of laser beam were measured.
The Cr:ZnSe crystal grown by the Bridgeman method was demonstrated as an efficient broadly tunable laser active
material generated radiation in the mid-infrared spectrum and operated in room-temperature.
Tunable mid-infrared laser radiation sources are of interest for many applications in spectroscopy, ranging,
remote-sensing, medical diagnosis and treatment and also for pumping nonlinear (OPO) and laser materials.
The ZnSe:Cr2+ is a promising laser active material for lasing in the range of 2-3 μm. Up to now number of
sources have been used for pumping ZnSe:Cr2+ active medium: Er-fibre laser, color-center laser, Co:MgF2
laser, Tm lasers, and Raman-shifted Nd:YAG laser [1-4].
In our study we have demonstrated, characterized and compared ZnSe:Cr2+ laser coherently pumped either
by flashlamp-pumped Er:YAP (wavelength 1.66 μm) or diode pumped Tm:YAP (wavelength 1.97 μm) laser
radiations.
For the case of ZnSe:Cr2+ laser pumping by wavelength 1.66 μm, the Er:YAP laser was constructed. From
the measured output radiation characteristics followed that the maximal ZnSe:Cr 2+ laser output pulse energy
was 5.5 mJ (slope efficiency 23%), and the length of pulse 120-160 μs. With the help of dispersive prism
inside the resonator, the generated laser radiation was tunable from 2100 nm to 2450 nm with only 2 times
drop in laser efficiency. The temporal profile and spatial structure of the generated laser beam were
measured.
Consequently, the diode-pumped Tm:YAP laser was constructed for coherently pumped ZnSe:Cr2+ laser.
LIMO laser diode (40 W) was used for longitudinal pumping of Tm:YAP laser. The output characteristics
and tuning curves were measured for various ZnSe:Cr2+ laser resonator arrangements and also for various
pumping radiation conditions in pulsed regime (pulse duration, repetition rate, duty cycle).
The maximal obtained ZnSe:Cr2+ laser output pulse energy was 0.35 mJ for the Tm:YAP pump pulse energy
13.5 mJ (pulse radiation 5 ms, repetition rate 20 Hz). The generated laser radiation was tunable from 2100
nm to 2450 nm. The temporal profile and spatial structure of the generated laser beam were measured.
The purpose of this work was to determine the relative efficiencies of new Nd3+-doped laser active/Raman - tungstate, molybdate, and fluoride - materials (SrWO4, PbWO4, BaWO4, SrMoO4, PbMoO4, SrF2, and LaF3) under selective longitudinal optical pumping by the alexandrite (~750nm), or diode (~800nm) laser. Crystals with various length, orientations and active ions concentrations were tested. To optimize the output of the tested lasers a set of input dichroic and output dielectric mirrors with different reflectivities were used. For realized lasers operating at pulsed free-running regime, threshold energy, slope efficiency, emission wavelength, and radiation polarization were determined. For each crystal, fluorescence lifetime and absorption coefficient under given pumping were established. The slope efficiency in case of Nd3+:PbMoO4 laser at wavelength 1054nm was measured to be 54.3% with total efficiency of 46% which is the best result obtained for all new tested crystals. For Nd3+ doped SrWO4, PbWO4, and BaWO4 crystals simultaneous laser and self-Raman emission were demonstrated in Q-switched regime. Thus newly proposed laser Raman crystals demonstrate high efficiency for Nd3+ laser oscillations comparable with well known and widely used Nd:KGW crystal. Further improvement in the quality of tungstate and molybdate type crystals should result in further increase in lasing efficiency at 1.06μm wavelength. Self Raman frequency conversion of Nd3+-laser oscillations in these crystals should result in high efficient pulse shortening, high peak power and new wavelengths in 1.2-1.5μm wavelength region.
Properties of the laser operation and simultaneously stimulated Raman scattering in the new SRS-active neodymium doped SrWO4 crystal coherently end-pumped by alexandrite 752 nm laser radiation were investigated. The maximum generated energy 90 mJ from the free-running Nd3+:SrWO4 laser at 1057 nm wavelength was obtained with the output coupler reflectivity 52%. The slope efficiency reached s = 0.52, the beam characteristic parameters M2 and divergence q were 2.5 ± 0.1, and 1.5 ± 0.1 mrad, respectively.
Maximal output energy of 1.46 mJ for the fundamental wavelength was obtained for Q-switched Nd3+:SrWO4 oscillator with a double Fabry-Perrot as the output coupler (R = 48%), and with the 5% initial transmission of LiF:F2- saturable absorber. Up to 0.74 mJ energy was registered at the first Stokes frequency. The pulse duration was 5 ns and 2.4 ns for the fundamental and Stokes radiation, respectively. The energy of 1.25 mJ at 1170 nm was obtained for closed Raman resonator with special mirrors.
For the case of mode-locking, two dye saturable absorbers (ML51 dye in dichlorethan and 3955 dye in ethanol) were used and SRS radiation in the form of pulse train was observed. The influence of the various Raman laser output couplers reflectivity as well as the initial transmissions of passive absorbers were investigated with the goal of the output energy maximization at the Stokes wavelength. In the output, the total measured energy was 1.8 mJ (for ML51 dye) and 2.4 mJ (for 3955 dye). The SRS output at 1170 nm was approximately 20% of total energy.
Stimulated Raman scattering in BaWO4 crystal under high-energy pumping of a self-phase-conjugated LiF:F2- Q-switched Nd:GGG laser is investigated. The output Stokes radiation obtained has the pulse train energy of up to 2 J, the peak power of up to 1 MW, and the conversion efficiency of up to 20%.
New Nd:SrWO4 and SrMoO4 crystals (45 mm and 33 mm of legnth, respectively) were investigated as Raman frequency converters of 50 picosecond Nd:YAG pulses and compared with already previously measured BaWO4 and KGd(WO4)2(KGW) tungstate crystals (33 mm and 40 mm of length, respectively). A forward SRS action was achieved in both new crystals. During the experiment the threshold energy of stimulated Raman process, generated wavelengths, and conversion efficiencies were measured. Single-pass first Stokes conversion efficiencies reached 25% and 21% for Nd:SrWO4 and SrMoO4 crystals, respectively. These values were compared with the maximal first Stokes efficiencies of previously studied crystals measured in the same experimental setup yielding: BaWO4 (η = 25% and KGW (η = 22%). As concerned the threshold - it was comparable for BaWO4, Nd:SrWO4, and SrMoO4. The SRS effect in KGW crystal started for ~25% higher pump energy. Our study shows that new Nd:SrWO4 and SrMoO4 crystals are other promising materials for picosecond Raman generation.
For a number of neodymium doped fluoride crystals both with regular and disordered structure the Judd-Ofelt analysis of absorption spectra have been performed, and fluorescence and lasing spectra were studied in order to reveal the most promising materials for optical amplification in a 1.3 micrometers telecommunication window. The most suitable crystalline media investigated was found to be cubic disordered fluorides based on (50 - 70%) SrF2 - (50 - 30%) CaF2 solid solutions with Nd3+ optical centers having tetragonal local symmetry. These crystals have (1) low value of excited state absorption line strength, (2) high metastable level lifetime (1.2 - 1.3 ms), (3) high enough emission cross section for fluorescence (approximately 4 X 10-21 cm2), and (4) proper fluorescence peak at about 1310 nm wavelength and comparatively wide fluorescence band with about 20 nm FWHM.
Passive Q-switching of 1.3 micrometers neodymium lasers with Nd2+:SrF2 and V3+:YAG crystalline saturable absorbers are studied. Giant pulses up to 5 mJ energy and 40 ns duration were obtained. Efficient Raman shifting of the 1.3 micrometers pulses of passively Q-switched lasers to 1.55 micrometers wavelength are realized in Ba(NO3)2 crystal.
Spectroscopic and laser properties of Cr,Nd:GGG and Nd:YAG crystals in the 1.3 - 1.45 micrometers wavelength range have been compared. Flashpumped Cr,Ce,Nd:GGG laser operating at 1.331 micrometers with total efficiency up to 3% and average output power of 65 W has been developed. For the first time to our knowledge oscillation at 1.4237 micrometers wavelength in Cr,Nd:GGG crystal have been obtained. Output energy of 2.3 J at this eyesafe wavelength with total efficiency of 1.23% have been obtained for flashpumped Cr,Ce,Nd:GGG laser in free-running mode. Average output power of 21.6 W at 13 Hz repetition rate have been achieved. Cr,Nd:GGG crystals advantages for 1.4 micrometers lasing compared to Nd:YAG crystals are discussed.
The Czochralski crystal growth of pure Cr, Er and Ho doped as well as Cr,Er and Cr,Ho codoped yttrium silicate Y2SiO5 (YSO) is reported. The growth conditions for producing the inclusion free single crystals of high optical quality are discussed. Spectroscopic properties of the singly doped and codoped material at room temperature are compared. Energy transfer processes from Cr4+ ions to Ho3+ and Er3+ ions in YSO host have been demonstrated for the first time.
The paper treats the problems of growth of large defectless single crystals of gadolinium- gallium garnet (GGG) doped with chromium, cerium, and neodymium, up to 65 mm in diameter and 130 mm long. The influence of UV radiation of the pump flashlamp on the formation of stable color centers in GGG-crystals co-doped with Cr, Ce, and Nd-ions was investigated. The processes of a nonradiative energy transfer from Cr to Nd ions in GGG were analyzed. The lasing properties of the GGG:Nd and GGG:Cr,Ce,Nd crystals were studied at 4F3/2 yields 4I11/2 and 4F3/2 yields 4I13/2 transitions. On the basis of grown crystals efficient lasers with the wavelengths of 1.06 and 1.33 micrometers are developed.
A study of populations inversion formation in a chemically pumped mixing shock driven CO2?GDLhas been conducted. ColdN2O injection was made in parallels into a hot flow with a chemical composition 25%CO + 25%He + 50%Ar by means of a central-body-type injector. The experiments were carried out with the coordinates of the in jeotion point 5 mm, 4 mm, 3 mm, 2 mm before critical section of a nozzle and 0.4 mm behind critical section. Diagnostics of the supersonio flow was performed by means of a gain for 10.6 ?m in CO2-laser transition, intensity of IR emission of C02 in a 4.3 ?n band and intensity of visible chemiluminescence CO + O ? CO2 + hv recordings. Prom the measured values of the gain and intensity of IR emission vibrational temperatures of the laser levels were determined.
The largest values of the gain up to 0.7 m-1 were obtained when the injection was in a 3 mm before critical section. The gain was recorded in the experiments with the injection in a 0.4 mm behind critical section. Chemical reactions occurred in each experiment in which stagnation temperature behind reflected shockwave exceed 1700 K. Vibrational temperature of the upper laser level in the experiments with reacting mixture was f ound to be considerably exceeding that in the experiments with inert mixture with a composition conformed to a composition of reacting mixture after completion of chemical conversions. The exceeding monotonously increased from 500 K to 900 K when the injection coordinate changed from 5 mm before to 0.4 mm behind critical section. Analogous exceeding of the lower laser level temperature reached 300 K. A strong chemiluminiscence was detected in
the experiments with reacting mixture. Thus , quasy—stationary chemical pumping of CO2 vibrat ions by reactions o N2O with CO occurred in the nozzle o GDL was firstly observed.
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