Laser-induced damage threshold (LIDT) of dielectric coatings prepared on monocrystalline neodymium-doped yttrium aluminium garnet (YAG) substrates was studied. Various coating designs were prepared using either reactive or ionassisted e-beam deposition technology and tested at 1030 nm 10 ns in r-on-1 mode according to the ISO 21254 standard. Measured damage thresholds were compared and LIDT was discussed with respect to thin-film design and coating technology.
So-called hybrid mirrors consists of broadband metallic surface coated with high reflection dielectric multilayer designed for specific wavelength. Such reflectors become more important with progressing development of multiband laser sources realized using parametric down conversion system, in particular for ultrashort-pulsed sources. Multiple pulse picosecond laser induced damage on such mirrors, tested by s-on-1 ISO-compliant method, is important part in development of such components, as there is a need in feedback predicating performance of novel designs. In following paper, we examine laser damage performance of several different designs of silver protected mirrors equipped with HR coating at 1030 nm.
Optical glasses, in particular fused silica and BK7, are the most common and used substrates for components manufacturing in laser technology and optics in general. Dielectric coating technologies for those materials are well known and established; both high-reflective and anti-reflective coatings prepared on such substrates demonstrated laser induced damage threshold (LIDT) exceeding tens J·cm-2 in nanosecond regime. However, LIDT became a major issue in further exploitation of crystalline materials as yttrium aluminum garnet (YAG) crystals, which often serves as a host in laser media and would be used in other components as well. One of the current challenge is the ability to transfer thin film coating technology used on glass to YAG in order to reach the same performance as in the case of fused silica or BK7 counterparts. HR dielectric coatings prepared on fused silica, BK7 and YAG substrates by reactive or ion-assisted e-beam deposition technique were tested on LIDT by s-on-1 method according to the ISO standard recommendations. Results from tests are presented and discussed in following paper.
Several sets of fused silica and BK7 windows were anti-reflection (AR) coated for 1030 nm wavelength using ion assisted e-beam deposition under various conditions (substrate temperature, ion-beam energy). Samples were tested for laser-induced damage threshold (LIDT) at 1030 nm, 10 ns with 10 Hz repetition rate in 1000-on-1 mode according to ISO 21254 standard. Measured damage thresholds at normal (0 deg) incidence were compared and discussed.
The influence of pumping beam diameter on output of the room-temperature operated Q-switched longitudinally diode-pumped Yb:YAG microchip laser was investigated. The tested microchip laser was based on monolith crystal (diameter 3mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.% Yb/Y, 3mm long) and saturable absorber (Cr:YAG crystal, 1.36mm long, initial transmission 90% @ 1031 nm). The microchip resonator consisted of dielectric mirrors directly deposited on the monolith surfaces. The pump mirror (HT for pump radiation, HR for generated radiation) was placed on the Yb:YAG part. The output coupler with reflection 55% for the generated wavelength was placed on the Cr3+-doped part. For longitudinal pumping, fibre coupled (core diameter 400 ¹m, NA= 0:22) laser diode was used. The diode was operating in pulsed regime (repetition rate 20 Hz, pulse length 3 ms, maximum pumping energy 95 mJ, wavelength 934 nm). Three various pumping optics offering pumping beam radius 0.20, 0.27, and 0.34mm were used. The wavelength of microchip laser emission was 1031 nm. The pumping beam radius did not signficantly influenced the pulse duration which was 1:5 § 0:3 ns (FWHM) in all three cases. The highest generated single Q-switched pulse energy (1.08 mJ) was obtained for pumping beam radius 0.27mm for maximum pumping. The corresponding peak power was 0.72MW.
The influence of temperature (from 80 up to 400 K) on emission of microchip lasers based on Nd:YAG crystal together with its spectroscopic properties was investigated. Three microchip lasers primarily designed for emission at 1.06, 1.32, and 1.44 μm, were tested. For all three lasers, the same parameters of Nd:YAG rod were used (Nd-doping » 0:9 at.% Nd/Y, length of 5 mm, diameter 5 mm). Resonator mirrors were deposited directly on the laser crystal faces. The output coupler transmission for desired wavelength was 2-5 %. The microchip lasers were placed in the temperature controlled cupreous holder inside vacuum chamber of the liquid nitrogen cryostat. The lasers were longitudinaly pumped by 808nm fibre-coupled pulsed laser diode (pulse duration 10 ms, repetition rate 10 Hz, maximum pumping power amplitude 10.5 W). The output microchip laser emission wavelength, laser threshold, laser slope efficiency, and laser beam profile were measured in temperature range from 80 up to 400 K. It was found that temperature strongly influenced mainly the laser beam profile and divergence which is rising with temperature (about 120% per 100 K). There exists also a significant influence on laser emission wavelength. Rich set of laser emission lines were obtained with these three lasers: 1061 and 1064nm (1.06 μm laser), 1318, 1332, 1338, and 1354nm (1.32 μm laser), and 1354, 1412, and 1444nm (1.44 μm laser). Generally, a higher temperature caused a longer emission wavelength. The temperature influence on lasers input-output characteristics was not so strong. For all three samples the best results were obtained for temperature in range 200-250 K. The highest laser slope and lowest threshold power were following: 60% and 0.8W (1.06 μm laser), 44% and 1.2W (1.06 μm laser), and 16% and 1.7W (1.44 μm laser).
Several sets of polished substrates were manufactured from monocrystalline yttrium-aluminium-garnet (YAG) grown by the Czochralski method. Samples were coated by both narrow-band and broad-band dielectric anti-reflection (AR) thin-film system prepared using either reactive or ion-assisted e-beam deposition technology and tested for laser-induced damage threshold (LIDT) at 1030 nm 10 ns in s-on-1 mode according to the ISO 21254 standard. Measured damage thresholds at normal (0 deg) incidence were compared for different thin-film designs and coating technology.
Yttrium aluminum garnet (YAG) crystals are one of the most important materials for active media in solid-state laser technology. Reach for higher energies brings more stress into crystals thin film coatings field, where methods used in the past are not sufficient anymore. Laser induced damage threshold (LIDT) became a major issue in further exploitation of YAG crystals as required extraction fluencies exceed tens J·cm-2 in nanosecond regime. Consequently, improved coating techniques based on e-beam deposition were introduced in order to improve damage resistance of active media. Thin films prepared on YAG crystals either by reactive or ion-assisted e-beam deposition technique were tested on LIDT by son- 1 method according to the ISO standards recommendations and results are presented in following paper.
In the last decade, lasers found a number of indications in dentistry. However, there is still one problem: the narrow spectrum of usefulness for individual radiation wavelengths. The aim of our study is to demonstrate the use of a compact three-frequency pulsed Nd-YAG laser for more than one treatment, namely disinfection, coagulation, selective ablation, and soft tissue removal. The laser wavelengths and the maximal energies achieved were the following: 1.06 um, 1.32 um, 1.44 um and 830 mJ, 425 mJ, and 200 mJ, respectively. It has been found that all of the investigated wavelengths exhibit disinfection properties. Moreover, radiation of 1.06 um wavelength removes soft tissue and exhibits also coagulation properties. Radiation of 1.44 um is most useful for selective ablation of initial caries and disinfection, and 1.32 um radiation can be used for precise ablation when higher energy is applied.
A CW operating, compact, high-power, high-efficient diode pumped 1064nm laser, based on Nd:YAG active medium, was developed for optical surface scanning and mapping applications. To enhance the output beam quality, laser stability, and compactness, a microchip configuration was used. In this arrangement the resonator mirrors were deposited directly on to the laser crystal faces. The Nd-doping concentration was 1 at.% Nd/Y. The Nd:YAG crystal was 5mm long. The laser resonator without pumping radiation recuperation was investigated {the output coupler was transparent for pumping radiation. For the generated laser radiation the output coupler reflectivity was 95%@1064 nm. The diameter of the samples was 5 mm. For the laser pumping two arrangements were investigated. Firstly, a fibre coupled laser diode operating at wavelength 808nm was used in CW mode. The 400 ¹m fiber was delivering up to 14W of pump power amplitude to the microchip laser. The maximum CW output power of 7.2W @ 1064nm in close to TEM00 beam was obtained for incident pumping power 13.7W @ 808 nm. The differential efficiency in respect to the incident pump power reached 56 %. Secondly, a single-emitter, 1W laser diode operating at 808nm was used for Nd:YAG microchip pumping. The laser pumping was directly coupled into the microchip laser using free-space lens optics. Slope efficiency up to 70% was obtained in stable, high-quality, 1064nm laser beam with CW power up to 350mW. The system was successfully used for scanning of super-Gaussian laser mirrors reflectivity profile.
Q-switched microchip laser emitting radiation at wavelength 1338nm was tested as a radiation source for laser induced breakdown spectroscopy (LIBS). This laser used sandwich crystal which combined in one piece the cooling part (undoped YAG crystal 4mm long), the active laser part (Nd:YAG crystal 12mm long), and the saturable absorber (V:YAG crystal 0.7mm long). The diameter of this crystal was 5 mm. The microchip resonator consisted of dielectric mirrors directly deposited on the monolith crystal surfaces. The pump mirror (HT @ 808 nm, HR @ 1.3 ¹m) was placed on the undoped YAG part. The output coupler (R = 90% @ 1338 nm) was placed on the V:YAG part. The fibre-coupled 808nm pumping laser diode was operating in pulsed regime (rep. rate 250 Hz, pulse width 300 ¹s, pulse energy 6 mJ). Using this pumping, stable and high reproducible Q-switched pulses were generated at wavelength 1338 nm. Pulse length was 6.2 ns (FWHM) and the mean output power was 33mW. The single pulse energy and peak power was 0.13mJ and 21kW, respectively. Laser was operating in fundamental TEM00 mode. The laser radiation was focused on a tested sample using single plano-convex lens (focal length 75 mm). The focal spot radius was 40 ¹m. The corresponding peak-power density was 0.83GW/cm2. The laser induced break-down was successfully reached and corresponding laser-induced plasma spectra were recorded for set of metallic elements (Cu, Ag, Au, In, Zn, Al, Fe, Ni, Cr) and alloys (Sn-Pb solder, duralumin, stainless-steel, brass). To record the spectra, StellarNet BLACK-Comet concave grating CCD-based spectrometer was used without any special collimation optics. Thanks to used laser wavelength far from the detector sensitivity, no special filtering was needed to overcome the CCD dazzling. The constructed laser could significantly improve repletion-rate of up-to-date LIBS devices.
Several sets of mirror samples with multilayer system Ta2O5/SiO2 on silver metal layer were manufactured using either PVD or IAD coating technology. Both BK7 and fused silica substrates were used for preparation of samples. Laserinduced- damage-threshold (LIDT) of metal-dielectric mirrors was tested using a laser apparatus working at 1030 nm wavelength, in ns and ps pulse length domains in S-on-1 test mode. The measured damage threshold values at 45 deg angle of incidence and P-polarization were compared for different pulse length, substrate materials and coating technology.
So-called hybrid mirrors, consisting of broadband metallic surface coated with dielectric reflector designed for specific
wavelength, becoming more important with progressing development of broadband mid-IR sources realized using
parametric down conversion system. Multiple pulse nanosecond laser induced damage on such mirrors was tested by
method s-on-1, where s stands for various numbers of pulses. We show difference in damage threshold between common
protected silver mirrors and hybrid silver mirrors prepared by PVD technique and their variants prepared by IAD.
Keywords: LIDT,
Compact, high-efficient, side-pumped monolithic Nd:YAG slab laser is presented. Designed active crystal shape ensures four internal reflections of generated laser radiation forming a ring resonator with high gain. A horizontal projection of the active medium form was a isosceles trapezoid with 18.6 mm long base, and 5 mm height. The angels between long base and legs are 87 deg. The thickness of the slab was 4 mm. Both base-sides and one leg-side was high reflective for lasing radiation. Second leg-side was partially reflective for lasing radiation and serves as an output coupler. The longer base-side was highly transparent for pumping radiation. The opposite base-side was highly reflecting for pump. To increase the pump absorption efficiency Nd-doping concentration was 1.4 % Nd/Y. As a pump source, single-bar quasi-cw fast-axis collimated laser diode JOLD-180-QPFN (Jenoptik) with peak power 180 W at 808 nm and output beam 10 0.9 mm without any further optics was used for slab side-pumping. The pumping pulses with repetition rate 5 Hz were 250 μs long (maximum pump energy 39 mJ). The Nd:YAG laser was operated at 1.06 µm. Two external mirrors (one totally reflecting, second with reflectivity 80 % at 1.06 μm) were used to form the oscillator. The laser was tested in the free-running regime. The maximum laser output energy reached was 5.9 mJ which corresponds to optical-to-optical efficiency of 15 %. The laser slope efficiency in respect to laser diode output was 20 %. The divergence of multimode output beam was 7 × 2.5mrad.
The goal of this work was an investigation of the temperature influence (in range from 80 up to 320 K) on the laser properties of Yb:YAG/Cr:YAG Q-switched diode-pumped microchip laser. This laser was based on monolith crystal (diameter 3mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.% Yb/Y, 3mm long) and saturable absorber (Cr:YAG crystal, 1.36mm long, initial transmission 90% @ 1031 nm). The laser resonator pump mirror (HT for pump radiation, HR for generated radiation) was directly deposited on the Yb:YAG monolith part. The output coupler with reflection 55% for the generated wavelength was placed on the Cr:YAG part. The microchip laser was placed in the temperature controlled cupreous holder inside vacuum chamber of the liquid nitrogen cryostat. For Yb:YAG part longitudinal pulsed pumping (pumping pulse length 2.5 ms, rep-rate 20 Hz, power amplitude 21W) a fibre coupled (core diameter 400 μm, NA= 0:22) laser diode, operating at wavelength 933 nm, was used. The microchip laser mean output power, pulse duration, repetition rate, emission wavelength, and laser beam profile were measured in dependence on temperature. The generated pulse length was in range from 2.2 ns to 1.1 ns (FWHM) with the minimum at 230 K. The single pulse energy was peaking (0.4 mJ) at 180 K. The highest peak power (325 kW) was obtained at 220 K. The highest pulse repetition rate (38 kHz) and output mean power (370mW) was reached for temperature 80 K.
The analysis of the disinfection effect of Nd:YAG laser radiation was investigated for patients with high
concentration of Streptococcus mutans in saliva (positive result in Saliva-check mutans test). For the interaction the
Nd:YAG laser system generated separate switchable wavelengths with the maximum output energies 1.1, 0.6, and
0.3 J for wavelength 1.06 μm, 1.32, μm and 1.44 μm, respectively, was used. Our study proved that after the laser
irradiation the Saliva-check test showed negative presence of Streptococcus mutans. The disinfection effect was
confirmed for all used radiation wavelength. For 1.44 μm this effect was reached with a smallest energy density.
Four sets of mirror samples with multilayer system SiO2/Ta2O5 on silver metal layer were manufactured using modified coating technology of the metal layer. Both BK7 and fused silica substrate materials were used. Laser-induced-damage-threshold of mirrors was tested using a laser apparatus working at 1030 nm wavelength, 3 ps pulse length at 1 kHz repetition rate and in 105- on - 1 test mode. The measured damage thresholds values at 45 deg incidence and Ppolarization were compared for different substrate materials and different technology of the metal layer preparation. Additionally four sets of samples with silver layer covered by SiO2 protecting monolayer were manufactured and tested for the comparison.
The spectral characteristics of laser active media, and thus those of the laser output, are temperature dependent. Specifically, in almost every crystal host, cooling to low temperatures leads to better heat removal, a higher efficiency and output power, and a reduced lasing threshold. Tm-ion doped lasers have an emission wavelength around 2 μm and are important in medicine for soft tissue cutting and hemostasis, as well as in LIDAR or atmosphere sensing technology. This paper presents the performance-temperature dependency of a 4 at. % doped Tm:YAP microchip. During the experiment the Tm:YAP crystal was placed inside an evacuated liquid nitrogen cryostat on a cooling finger. As its temperature was varied from 80 K to 340 K, changes were observed in the absorption spectrum, ranging from 750 nm to 2000 nm and in the fluorescence spectrum from 1600 nm to 2050 nm. Fluorescence lifetime was seen to rise and fall with decreasing temperature. The laser was pumped by a 792 nm laser diode and at 80 K the maximum output peak power of the laser was 4.6 W with 23 % slope efficiency and 0.6 W threshold, compared to 2.4 W output peak power, 13 % slope efficiency and 3.3 W threshold when at 340 K. The laser emission wavelength changed from 1883 nm to 1993 nm for 80 K and 300 K, respectively.
V:YAG crystal was investigated as a passive Q-switch of longitudinally diode-pumped microchip laser, emitting radiation at wavelength 1030.5 nm. This laser was based on diffusion bonded monolith crystal (diameter 3 mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.% Yb/Y, 3 mm long) and saturable absorber (V:YAG crystal, 2 mm long, initial transmission 86 % @ 1031 nm). The microchip resonator consisted of dielectric mirrors directly deposited on the monolith surfaces (pump mirror HT @ 968 nm and HR @ 1031 nm on Yb:YAG part, output coupler with reflection 55 % @ 1031 nm on the V:YAG part). For longitudinal CW pumping of Yb:YAG part, a fibre coupled (core diameter 100 μm, NA = 0.22, emission @ 968 nm) laser diode was used. The laser threshold was 3.8W. The laser slope efficiency for output mean in respect to incident pumping was 16 %. The linearly polarized generated transversal intensity beam profile was close to the fundamental Gaussian mode. The generated pulse length, stable and mostly independent on pumping power, was equal to 1.3 ns (FWHM). The single pulse energy was increasing with the pumping power and for the maximum pumping 9.7W it was 78 μJ which corresponds to the pulse peak-power 56 kW. The maximum Yb:YAG/V:YAG microchip laser mean output power of 1W was reached without observable thermal roll-over. The corresponding Q-switched pulses repetition rate was 13.1 kHz.
The aim of this study was to investigate whether refractive power of thermal lens for Yb:LuAG crystal at cryogenic temperatures depends on Yb doping concentration which has not been examined yet. The three measured Yb:LuAG laser rods samples (length of 3 mm, diameter 3 mm, AR @ 0.94 μm and 1.03 μm, doping concentration 5.4, 8.4 and 16.6 at. % Yb/Lu) were mounted in the temperature controlled copper holder of the liquid nitrogen cryostat. Samples were longitudinally pumped with fiber coupled CW laser diode at 0.930 μm with the focal point 0.4 mm in diameter. The 38 mm long semi-hemispherical laser resonator consisted of a flat pump mirror (HR @ 1.03 μm and HT 0.94 μm) and curved output coupler (r=500 mm) of reflectivity 94 % @ 1.06 μm. The refractive power of thermal lens was estimated indirectly by measuring of change in the position of focused laser beam focal point. The measurement was performed for constant absorbed power of 10 W in temperature range from 80 up to 240 K. It was observed that cryogenic cooling caused reduction of thermal lens power, which increased linearly with increasing temperature. For temperatures from 80 to 160 K refractive power was identical for all concentration. For higher temperature the refractive power of thermal lens increased with increasing Yb3+ concentration. Presented study shows that application of cryogenic temperature leads to reduction of thermal effect even for high dopant concentration in Yb:LuAG crystal. This is essential for reaching of high output power while maintaining high beam quality.
The highly-stable Q-switched longitudinally diode-pumped microchip laser, emitting radiation at wavelength 1031 nm, was designed and realized. This laser was based on monolith crystal which combines in one piece an active laser part (YAG crystal doped with Yb3+ ions, 10 at.% Yb/Y, 3mm long) and saturable absorber (YAG crystal doped with Cr3+ ions, 1.36mm long). The diameter of the diffusion bonded monolith was 3 mm. The initial transmission of the Cr:YAG part was 90% @ 1031 nm. The microchip resonator consisted of dielectric mirrors directly deposited on the monolith surfaces. The pump mirror (HT for pump radiation, HR for generated radiation) was placed on the Yb:YAG part. The output coupler with reflection 55% for the generated wavelength was placed on the Cr3+-doped part. Q-switched microchip laser was tested under CW diode pumping. For longitudinal pumping of Yb:YAG part, a fibre coupled (core diameter 100 μm, NA= 0.22) laser diode, operating at wavelength 968 nm, was used. The laser threshold was 3.3W. The laser slope efficiency calculated for output mean power in respect to incident CW pumping was 17%. The wavelength of linearly polarized laser emission was fixed to 1031 nm. The generated transversal intensity beam profile was close to the fundamental Gaussian mode. The generated pulse length was equal to 1.6 ns (FWHM). This value was mostly stable and independent on investigated pumping powers in the range from the threshold up to 9.3W. The single pulse energy was linearly increasing with the pumping power. Close to the laser threshold the generated pulse energy was 45 μJ. For maximum investigated CW pumping 9.3W the pulse energy was stabilized to 74 μJ which corresponds to the Q-switched pulse peak power 46 kW. The corresponding Q-switched pulses repetition rate was 13.6 kHz. The maximum Yb:YAG/Cr:YAG microchip laser mean output power of 1W was reached without observable thermal roll-over.
Laser induced damage threshold is a key parameter for all components in high-power laser system, establishing limits of
maximum achievable energy, and consequently average power. To provide reliable and stable laser sources, desirable
both in academic and industrial area, involved components has to be tested and meet certain quality criteria. To provide
such laser source is the goal of HiLASE project, where the development of scalable kW-class laser delivering ps pulses
in kHz repetition rate is taking place. Broadband, high damage threshold mirrors are one of the key components for
future installations and their development is carried out synergistically with laser system and LIDT station.
Laser-induced-damage-threshold of two types of metal-dielectric mirrors was tested using a laser apparatus working at
800 nm wavelength with 1 ps pulse length at 1 kHz repetition rate and in 106-on-1 test mode. Four sets of mirror
samples with different layer system designs using a multilayer Ta2O5/SiO2 coating on silver or gold metal layer were
manufactured. Both BK7 and fused silica substrate materials were used for manufacturing of samples. The measured
damage thresholds at 45 deg incidence and P-polarization were compared with computed properties of layer system and
used materials.
Laser-induced-damage-threshold (LIDT) of polarizing Brewster-angle beam splitters based on two different layer system
designs was measured using a laser apparatus working at 1060 nm wavelength with 10 ns pulse length and 1-on-1 test
mode. Two sets of samples with different design of layer system using TiO2/SiO2 coating materials were examined. Both BK7 and fused silica substrate materials were used for manufacturing of samples. The measured damage thresholds in S- and P-polarization were compared with computed values of the internal electric field inside of the layer system and with computed values of absorption as a measure of integral interaction of laser beam throughout the layer system.
Two Yb:LuAG (Yb:Lu3Al5O12) plates (thickness 1.05 mm, diameter 3 mm, AR/AR @ 0.9 − 1.1 μm, Yb-doping c = 15% and 20 %) were prepared for laser experiments. For Yb:LuAG pumping, fibre coupled laser diode
operating in pulsed regime was used (fibre core diameter 100 μm, emission wavelength 968 nm, pulse length
2 ms, repetition rate 10 Hz, maximum energy 40 mJ). The longitudinally pumped Yb:LuAG was placed inside
the 148mm long resonator formed by a flat pumping mirror (HR @ 1.0 − 1.1 μm, HT @ 0.97 μm) and by a
curved output coupler (radius of curvature 150 mm). Set of output couplers with reflectivity R = 70 − 97% @
1.0−1.1 μm was used and the output power amplitude was measured in dependence on absorbed pumping power
amplitude. It was found that for both samples the output coupler reflectivity had only minor influence on laser
output parameters expect emission wavelength (1048nm for R < 90% and otherwise 1031 nm). The sample with
lower concentration had a lower threshold (∼ 2.5W for c = 15% and ∼ 3.0W for c = 20%) and higher slope
efficiency (∼ 61% for c = 15% and ∼ 50% for c = 20 %). The maximum output power amplitude 6.7W was
obtained using Yb:LuAG with c = 20% and R = 92% for pumping power amplitude 14W. Obtained results
confirmed the good quality of newly grown highly doped Yb:LuAG crystals.
The goal of our research is a compact Raman laser emitting short pulses with high energy and peak power in “eye-safe" region around wavelength 1.5 μm. We utilize intracavity conversion of giant pulses at wavelength 1.34 μm in a BaWO4 Raman crystal (18 mm long, AR coated). Required high energy and peak power was reached using a flash-lamp pumped Nd:YAG laser (rod 100 mm long, diameter 4 mm), Q-switched by V:YAG solid-state saturable absorber (initial transmission 37% @ 1.34 μm). The L-shaped oscillator for 1.34 μm radiation consisted of a concave mirror (r = 0.5 m, HR @ 1.3 μm, HT @ 1.06 μm), flat polarizing intracavity mirror, and output coupler (r = 1 m, HR @ 1.3 μm, R = 39 % @ 1.5 μm). The polarizing mirror ensured stable linearly polarized laser emission and prevented parasitic oscillations at 1.06 μm. The Raman laser oscillator was formed by the output coupler and another intracavity mirror (r = 0.5 m, HR @ 1.5 μm, HT @ 1.3 μm), inserted between BaWO4 and the polarizing mirror. For pumping energy of 28.2 J stable vertically polarized generation of the 1st Stokes radiation at 1528 nm was reached. In multimode operation the output energy was 20 mJ in 2.25 ns pulses. Single mode operation was possible by inserting a 1.5 mm aperture between Nd:YAG and V:YAG crystal. The output energy dropped to 9.7 mJ (even for higher pump power of 30.7 W) and output pulses were shortened to 1.87 ns.
As came out in one of our past experiments concerning the Pr:YAlO3 (Pr:YAP) active material, UV-radiation had an
adverse effect for lasing action due to the crystal solarization. So, co-doping of this material by Ce3+-ions having broad
absorption-bands in the UV-region has been proposed for crystal property improvement in terms of color-center
formation. The Pr,Ce:YAP absorption-spectrum investigation under UV-radiation exposure, in comparison to the
Pr:YAP one, is reported in this contribution. Moreover, lasing properties of these two materials under the GaN-diode
pumping are summarized.
Influence of Ce3+-ions in Pr,Ce:YAlO3 crystal on spectroscopic and laser characteristics has been investigated.
Spectroscopic properties and preliminary laser results of GaN-diode pumped Pr,Ce:YAlO3 active medium at room
temperature have been reported and compared with the same crystal without Ce3+-ion. Co-doping of the active medium
by Ce3+-ions was proposed for crystal property improvement in terms of color center formation caused by UV radiation.
A compact diode pumped Q-switched lasers, operating at wavelength 1031 nm, were based on the composite
crystal Yb:YAG/Cr:YAG. This composite crystal (diameter 3mm) consisted of diffusion bounded 3mm long
Yb:YAG (10 at.% Yb/Y) and 1.6mm long Cr:YAG crystal (initial transmission 85% @ 1031 nm). External
resonator allowing to tune generated Q-switched pulse parameters or microchip configuration offering the shortest
pulses and highest peak power were tested for this device. For longitudinal pumping of Yb:YAG gain medium,
fibre coupled (core diameter 200 μm, NA= 0.22) laser diode, operating at wavelength 968 nm, was used. In
the first case, Yb:YAG/Cr:YAG composite crystal was AR-coated and placed inside the 150mm long semihemispherical
resonator consisted of a flat pumping mirror (HR @ 1.01 − 1.09 μm, HT @ 0.97 μm) and curved
output coupler (r = 150mm) with reflectivity 70% @ 1031 nm. Generated pulses with the peak power 23 kW
were 17 ns long (FWHM). The highest generated pulse energy was 0.38 mJ. In the second case, the resonator
mirrors were deposited directly on the crystal faces. The output coupler reflectivity was 85% @ 1031 nm. In this
compact microchip configuration, 140 ps long (FWHM) pulses with energy 0.13mJ and peak power 0.92MW
were generated at wavelength 1031 nm.
Two samples of Er-Yb doped phosphate glass were tested as a gain medium of longitudinally diode pumped
laser. One sample was a simple Er:Yb:glass rod (length 2.8 mm), second sample was composite rod consisting of
2.8mm long Er:Yb:glass and 6mm long YAG crystal. Diameter of both samples was 6 mm. Dopant concentration
for Er:Yb:glass was 0.75 × 1020 cm−3 Er and 1.7 × 1021 cm−3 Yb. The goal of the experiment was to investigate
an effect of the undoped YAG cap on the Er:Yb:glass laser operation. The active medium, fixed in cupreous
heatsink, was placed inside the 150mm long resonator consisted of a flat pumping mirror (HR @ 1.52−1.65 μm,
HT @ 0.97 μm) and curved output coupler (r = 150 mm, R = 97% @ 1.52−1.61 μm). For Er:Yb:glass pumping a
fiber coupled laser diode, operating in pulsed regime, was used. The pumping pulse width, energy, and wavelength
were 1 ms, 10 mJ, and 975 nm, respectively. The decrease of Er:Yb:glass laser output pulse energy with increasing
pumping repetition rate was observed for both samples. In case of simple Er:Yb:glass the energy dropped from
1.4mJ to 0.6mJ after pumping duty cycle increase from 0.5% to 6 %. In case of composite YAG/Er:Yb:glass active
medium the relative output energy decrease was only 20% for pumping duty cycle increase from 0.5% to 10%.
This result showed that the slope of the output energy decrease with increasing duty cycle was approximately
four times slower for composite active media in comparison with simple Er:Yb:glass.
The impact of the V:YAG saturable absorber nonlinear transmission polarization anisotropy on Q-switched laser
system was investigated. Two various cuts ([111] and [100]) of V:YAG crystal with the same initial transmission
87% @ 1.3 μm were used as a passive Q-switch for longitudinaly diode pumped linearly polarized Nd:YAP
laser operating at 1342 nm. This laser consisted of 8.2mm long Nd:YAP crystal placed in 100mm long semihemisferical
resonator. The flat mirror in vicinity of Nd:YAP crystal was transparent for pumping radiation at
805nm and highly reflecting at operating wavelength 1342 nm. The curved output coupler (radius of curvature
146mm) had reflectivity 92% @ 1342 nm. The laser was tested under pulsed pumping for the duty-cycle 9%
and under CW pumping. The laser output parameters (mean output power, pulse width, repetition rate, energy,
and peak power) were measured for absorber turning around longitudinal crystal axis. In this configuration for
[111]-cut of V:YAG the pulse energy and pulse width (FWHM) varied from 27 up to 38 μJ and from 50 to
40 ns, respectively. This corresponds to peak power rise from 0.55 up to 0.95kW. In case of [100]-cut the proper
orientation of V:YAG in respect to oscillating radiation polarization allowed to increase pulse energy from 37
to 60 μJ and peak power from 1.3 to 3 kW. Simultaneously, the pulse width decreased from 28 to 20 ns. The
results showed that proper choice of saturable absorber cut and orientation can significantly improve giant pulse
parameters.
Laser characteristics of Pr:YAlO3 microchip laser operating in the near-infrared spectral region are reported. For active
medium pumping, GaN laser diode providing up to 1 W of output power at ~448 nm was employed. Microchip resonator
was formed by dielectric mirrors directly deposited on the Pr:YAlO3 crystal surfaces. The continuous-wave output
radiation at 747 nm with maximum power of 139 mW has been extracted from the microchip laser system. Slope
efficiency related to the incident pumping power was 25%.
Two saturable absorbers, V:YAG (V3+:Y3Al5O12) and V:LuAG (V3+:Lu3Al5O12), were compared as a passive
Q-switches for microchip laser based on Nd:YAG gain medium. The emission wavelength of this laser was in 1.3 μm spectral range. Two Q-switched monolithic microchip laser devices were prepared: Nd:YAG/V:LuAG and Nd:YAG/V:YAG. Active Nd:YAG part of both microchip lasers was the same (4mm long, 1.1 at.% Nd/Y).
The thickens of saturable absorbers ensured the same initial transmission (T0 = 85%) of the passive Q-switch
part (V:LuAG was 1.1mm long, V:YAG was 0.7mm long). The gain medium and the saturable absorber were diffusion bonded to form one monolithic crystal. The diameter of both crystals was 5 mm. Laser mirrors were deposited directly onto monolith faces. The output coupler with reflection 90% for the generated wavelength was
placed on the V3+-doped part. The pump mirror (HT@808 nm, HR@1.3 μm) was placed on opposite monolith face. Lasers were tested under longitudinal continuous diode pumping and results were compared. Both lasers generated linearly polarized radiation at wavelength 1338nm with the lasing threshold 8W. Comparing the giant
pulse parameters and the laser efficiency, the better results were obtained for Nd:YAG/V:YAG microchip laser.
The pulse duration (FWHM) in this case was shorter (2.16±0.04 ns) and more stable than in Nd:YAG/V:LuAG case (3.3 ± 0.5 ns). The obtained average pulse energy was slightly higher for Nd:YAG/V:LuAG microchip laser (45 μJ) than for Nd:YAG/V:YAG (41 μJ) laser. However, due to shorter pulse length higher peak power (18.5 kW) was obtained with V:YAG saturable absorber than with V:LuAG (13.7 kW).
Q-switched microchip laser emitting radiation at wavelength 1338nm was designed and constructed to obtain nanosecond laser pulses with multikilowatt peak power. This laser was based on a composite crystal which combines in one piece an active laser part (2mm long YAG crystal doped with Nd3+ ions 1.2 at.% Nd/Y) and a
saturable absorber (0.6mm long V3+:YAG). The initial transmission of the V:YAG part was ~ 85%@1.34 μm.
The diameter of the diffusion bounded monolith was 5 mm. The microchip resonator consists of dielectric mirrors directly deposited on the monolith surfaces. The pump mirror (HT for pump radiation @ 0.8 μm, HR for generated radiation @ 1.3 μm) was placed on the Nd:YAG part. The output coupler with reflection 90% @1.34 μm was placed on the V3+-doped part. To prevent a parasitic lasing at 1064 nm, the reflectivity of both this mirrors was minimized at this wavelength. The overall length of constructed microchip laser was 2.6 mm. Laser was tested under pulsed diode pumping (wavelength 808 nm, pulse length 300 μs, energy 5.1 mJ, repetition rate 25 Hz - 2 kHz). The generated pulse length was stable and it was equaled to 1.07 ± 0.02 ns. The wavelength of linearly polarized laser emission was 1338 nm. Up to the highest mean pumping power 10W, the output beam had well-defined Gaussian transversal profile with the half divergence angle not higher than 4 mrad. For the lowest pumping rep. rate, the generated pulse energy and peak power was 34 μJ and 33kW, respectively. For maximum
pumping rep. rate the pulse peak power was 14kW.
A preliminary investigation of the passively Q-switched resonantly pumped Er:YAG laser system operating at
wavelength 1645 nm has been performed. The output characteristics of the designed and constructed laser, i.e., the
output energy, temporal profile, and spatial beam structure were registered. The Er:YAG laser crystals longitudinally
pulse-pumped by Erbium glass laser radiation (repetition rate 0.5 Hz, wavelength 1535 nm) were investigated. The
passive Q-switch was a Co:MALO (Co2+:MgAl2O4) crystal.
To optimize the system, three Er:YAG crystals with various in Erbium/Yttrium concentration and length were studied
in the free-running regime. The curved pumping mirror of linear hemispherical oscillator had a high transmittance at the
pumping wavelength and maximal reflectance at the generating wavelength around 1645 nm. The output flat dielectric
coupler reflectance was 90 % at 1645 nm. Out of the three Er:YAG active laser crystals, the best output characteristics in
free running regime were reached for the medium with Er3+ concentration 0.2 at.% Er/Y and length 25 mm.
For the Q-switching, three saturable absorbers Co:MALO with various length, that is various transmission, were
investigated. These crystals had no anti-reflection layer and were placed between the active crystal and output mirror.
The laser resonator length was 162 mm. For an incident pump energy of 131 mJ, the 1.6 mJ Q-switched single pulse
energy with 58 ns pulse duration (FWHM) was obtained. The corresponding peak power was 28 kW. The spatial beam
structure was close to the fundamental profile.
We review blue generation of Pr:YAlO3 laser under flash-lamp and GaN-diode pumping at room temperature.
Stimulated emission at 373.5 nm reached by intracavity frequency doubling of the near-infrared-emitting Pr:YAP laser
operating at a fundamental wavelength of 747 nm in the continuous and pulsed regime is reported. With BBO crystal
employed as a nonlinear medium, 12.3 mW of continuous output power at 373.5 nm has been obtained, as well as stable
pulses with an output peak power of about 10 kW in the blue spectral region.
Compact Q-switched diode-pumped laser, emitting radiation at eye-safe wavelength 1444 nm, was studied. This
laser was based on composite crystal (diameter 5mm) consisting of 4mm long Nd:YAG active medium diffusion
bonded with 1mm long V:YAG saturable absorber (initial transmission @ 1444nm 94 %). The laser resonator
mirrors were directly deposited onto the composite crystal surfaces. These mirrors were designed to ensure
emission at 1444nm and to prevent parasitic lasing at other Nd3+ transmissions. The pump mirror (R < 10%
for pump radiation @ 808 nm, R < 2% @ 1064 nm, R < 15% @ 1330 nm, HR @ 1444 nm) was placed on the
Nd3+-doped YAG part. The output coupler with reflectivity 94% for the generated wavelength 1444nm was
placed on the V3+-doped part (R < 5% @ 1064 nm, R < 15% @ 1330 nm). Temperature dependence of giant
pulse energy and length was studied independently on pumping pulses duty cycle. It was found that for constant
duty cycle 1% and for crystal holder temperature rise from 8.2 up to 43.2 °C the pulse width dropped from 31
to 5.1 ns and pulse energy rose from 17 to 57 μJ. This represents a pulse peak power increase from 0.54 up to
11kW. From a mathematical model of passively Q-switched laser it follows that this behaviour can be explained
by temperature caused increase of ground-state absorption and ground-state to excited-state absorption ratio
(FOM) of V:YAG saturable absorber at wavelength 1444nm in case if FOM ~ 1.
Er:YAlO3 crystals as active materials for coherent resonant pumping by Er:glass laser were investigated. The Er:YAP
rods had 1 at.% concentration of Erbium/Yttrium (Er/Y) and were 10 mm or 20 mm in length. The output characteristics
of the designed and constructed lasers, i.e., the spatial beam structure, temporal profile, and efficiency were derived. For
555 mJ incident Er:glass pump energy (1535 nm wavelength), the generated output energy was 20 mJ at the lasing
wavelength 1623 nm. For comparison, three Er:YAG crystals with various Er/Y concentrations and lengths were also
evaluated under the same conditions. These lasers generated energy at 1648 nm. The main advantage of resonantly
pumped lasers is low quantum defect related with lower cooling demand. Therefore, with the used repetition rate 0.5 Hz,
it was not necessary to cool the active crystals.
In this paper we report on comparison of laser results reached by Pr-doped oxide and fluoride crystals under GaN-laser
diode pumping at room temperature. As oxide and fluoride crystal representatives, Pr:YAlO3 (Pr:YAP) and Pr:LiYF4
(Pr:YLF) crystals were used. Pumping was accomplished by multimode GaN-laser diodes capable of providing output
powers of up to 1W at wavelengths corresponding with Pr:YAP and Pr:YLF absorption peaks. For both samples,
efficient stimulated emission in the red laser transition has been demonstrated, and laser results regarding the output
power, threshold, and slope efficiency with respect to the absorbed power have been compared.
Successful second harmonic generation from the radiation of Pr:YAP laser has been demonstrated. The flash-lamp
pumped Pr:YAP laser was operated in Q-switched pulsed regime with 0.5 Hz repetition rate at room temperature. For Qswitching,
electro-optical modulator based on LiNbO3 Pockels cell in quarter-wave configuration was employed. The
pulses with an energy and length of 5 mJ and 50 ns were reached, respectively, at 747 nm wavelength. BBO crystal was
used for second harmonic generation, and output pulses with the 30 uJ energy and 34 ns length were generated at
373.5 nm wavelength.
Resonant pumping by a solid state Er:glass laser was successfully examined for Er:YAG and for the first time also
for Er:YAP laser. The maximal incident pumping energy on the wavelength 1535 nm was 640 mJ with a repetition rate
of 0.5 Hz; the corresponding pulse length was 1.9 ms (FWHM). The Er:glass laser radiation was focused into the active
crystal by a CaF2 lens with 70 mm focal length. The measured beam diameter in focal plane was ~ 400 μm.
The Er:YAG and Er:YAP rods had 10 mm in length and 5 mm in diameter. Various concentrations of Er3+ ions were
used: 0.5 at.% for YAG and 1 at.% for YAP crystal. The resonator consisted of pumping and output dielectric mirrors.
For both cases, the pumping dielectric mirror with high transmittance at pumping wavelength (T > 95 % @ 1532 nm)
and maximal reflectance at the oscillating wavelength (around 1640 nm) was used. The output coupler reflectance was
85 % and 90 % for 1532 nm and 1640 nm, respectively. The advantage of resonantly pumped lasers is low thermal load
corresponding to low quantum defect, and, therefore, it was not necessary to cool the active crystals.
The output generated energy for the Er:YAG laser medium was 45 mJ at 1648 nm for 465 mJ incident pumping energy.
For Er:YAP crystal the energy reached was 20 mJ at the lasing wavelength 1623 nm. The incident pumping was 640 mJ.
For both resonantly pumped laser systems other characteristics i.e., spatial beam structure, divergence, and efficiency
were investigated.
Successful room-temperature generation of Pr:YAP laser radiation at wavelengths of 747 nm and 662 nm was demonstrated. A flash-lamp pumped Pr:YAP laser was operated in free-running pulsed regime at room temperature. Permanent laser action was reached by means of a special UV color glass plate filter placed directly into the laser cavity. The maximum output energy and pulse length reached at wavelengths of 747 nm and 662 nm were 102 mJ, 92 μs and 6.1 mJ, 47.5 μs, respectively. The laser beam parameter M2 ~ 1.5 was measured when the 662 nm wavelength was generated. In the case of 747 nm wavelength generation, M2 ~ 1.2 was reached with a diaphragm inside the resonator. For different pumped energy values, the line shape and linewidth remained stable for both cases.
A CW operating, high-power, high-efficient diode pumped 2μm laser was based on Tm:YAP (Tm3+ doped
YAlO3) active medium. To enhance the output beam quality, laser stability, and compactness, a microchip
configuration was used. In this arrangement the resonator mirrors were deposited directly on to the laser crystal
faces. Two groups of laser crystals were tested - with doping 3 or 4 at.% of Tm/Y. In each group, laser resonators
without and with pumping radiation recuperation were investigated. The first one used 3mm long active medium
and output coupler was transparent for pumping radiation. The second one used only 2mm long active medium
but the pumping radiation, unabsorbed after first pass, was reflected back by the output coupler. For the
generated laser radiation the output coupler reflectivity was 97 %. The diameter of all samples was 3mm and the
a-cut (Pbnm) of Tm:YAP was used. For the laser pumping, a fibre coupled laser diode operating at wavelength
0.79 μm was used. The 400 μm fiber was delivering up to 25W of pump power to the coupling optics. All crystals
were studied under the same pumping and cooling conditions and results were compared. The best results were
obtained for 2mm long Tm:YAP crystal (3mm diameter, 4 at.% Tm3+). The output power 6.2W @ 1994nm
in linearly polarized close to TEM00 beam was obtained for incident pumping power 20.2W @ 793 nm. The
differential efficiency in respect to the incident pump power reached 34% while the maximal attained optical-tooptical
efficiency was ~ 31 %.
Successful room-temperature generation of the Pr:YAP laser radiation at a wavelength of 747 nm was demonstrated.
Flash-lamp pumped Pr:YAP laser was operated in free-running pulsed regime at room temperature. Permanent laser
action was reached by means of special UV color glass plate filter placed directly into the laser cavity. The maximum
output energy and the pulse length reached were 102 mJ and 92 μs, respectively, at 121 J pumping (pumping flash-lamp
pulse length was 110 μs). Stimulation emission excitation threshold was observed at 20 J.
Yttrium and Lutecium garnets (YAG and LuAG) doped by Chromium or Vanadium ions (Cr4+ or V3+) were
investigated as saturable absorbers potentially useful for passive Q-switching at wavelengths 1 μm and/or 1.3 μm.
For comparison also color center saturable absorber LiF:F-2 and Cobalt doped spinel (Co:MALO) were studied.
Firstly, low power absorption spectra were recorded for all samples. Next, absorbers transmission in dependence
on incident energy/power density was measured using the z-scan method. Crystals Cr:YAG, Cr:LuAG, V:YAG,
and LiF:F-2 were tested at wavelength 1064 nm. Therefore Alexandrite laser pumped Q-switched Nd:YAG laser
was used as a radiation source (pulse length 6.9 ns, energy up to 1.5 mJ). Crystals V:YAG, V:LuAG, and
Co:MALO were tested at wavelength 1338 nm. So diode pumped Nd:YAG/V:YAG microchip laser was used as a
radiation source (pulse length 6.2 ns, energy up to 0.1 mJ). Using measured data fitting, and by their comparison
with numerical model of a "thick" saturable absorber transmission for Q-switched Gaussian laser beam, following
parameters were estimated: saturable absorber initial transmission T0, saturation energy density ws, ground state
absorption cross-section σGSA, saturated absorber transmission Ts, excited state absorption cross-section σESA,
ratio γ = σGSA/σESA, and absorbing ions density. For V:YAG crystal, a polarization dependence of Ts was also
investigated. With the help of rate equation numerical solution, an impact of saturable absorber parameters on
generated Q-switched pulse properties was studied in plane wave approximation. Selected saturable absorbers
were also investigated as a Q-switch and results were compared with the model.
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.
We have compared two solid-state saturable absorbers for Q-switching of longitudinally diode-pumped Nd:YAG
laser operating at wavelength 1444 nm: vanadium doped garnet (V3+:Y3Al2O5, V:YAG), and cobalt doped spinel
(Co2+:MgAl2O4, Co:MALO). V:YAG crystal with initial transmission 91% was 2.2mm thick. Co:MALO crystal
with initial transmission 91% was 2.0mm thick. Q-switched laser consisted of the Nd:YAG composite rod (8mm
long Nd-doped part, 4mm long undoped YAG part) and the saturable absorber placed in 80mm long hemispheric
cavity. As an output coupler was used concave mirror (r = 150mm) with reflectivity 98% on lasing wavelength.
Giant pulses were obtained with both passive Q-switches. When V:YAG saturable absorber was used, 55 ns long
(FWHM) pulses were generated with peak power 0.47kW (pulse energy 26 &mgr;J). Using Co:MALO, more powerful
pulses were obtained (40 ns long, 1.0kW peak power, 45 &mgr;J energy). Advantage of less efficient V:YAG consist
in possibility of diffusion bonding between Q-switch and laser active medium which allows to prepare miniature
compact laser device. This concept was demonstrated by using of Nd:YAG/V:YAG monolith crystal (4mm long
undoped YAG part, 8mm long Nd:YAG part, 0.5mm long V:YAG part - initial transmission 97% @ 1444 nm).
This monolithic crystal, originally designed for 1338nm lasing, was placed into 23mm long cavity resonating
at wavelength 1444 nm. For output coupler reflectivity 96% pulses 39 ns long with peak power 0.64kW were
generated at wavelength 1444 nm.
For many applications, like micromanufacturing, remote sensing, data storage, etc. a microchip Nd:YAG laser is
suitable. From the measurement of the laser radiation transmission through the eye tissue is evident that the injury
probability of the retina is higher for the case of 1064 nm instead of 1338 nm. The main reason for that is the radiation
water absorption. The Q-switched diode pumped (at 808 nm) microchip laser emitting radiation at wavelength 1338 nm
was designed and realized. This laser was based on diffusion bonded crystal (diameter 5 mm) which combines in one
piece the laser active part (Nd:YAG, 4 mm long) and saturable absorber (V:YAG, 0.7 mm, T0 = 85%). The microchip
resonator mirrors were deposited directly on the bonded crystal surfaces, output coupler reflexivity was 90%. The
constructed "alignment-free" Q-switched microchip laser was tested under pulsed, and CW diode pumping. In both
cases, the generated pulse energy, pulse length, emission wavelength, polarization, and laser beam profile were
measured. The energy up to 18.6 &mgr;J in 1.7 ns long pulses was reached at the wavelength 1338 nm. TEM00 laser mode
was linearly polarized.
The interaction of the radiation from the near- and mid-infrared region with the eye tissue was investigated and as
conclusion the microchip with the wavelength 1338 nm was chosen as a good compromise between the eye safe 1.5 &mgr;m
radiation and commonly, in the application used, 1.06 &mgr;m radiation.
Two passively Q-switched Nd:YAG monolithic microchip laser devices were prepared by Nd:YAG and V:YAG
crystals diffusion bonding. Stable generation of nanosecond pulses at wavelength 1338nm was obtained. The first
laser, designed for higher mean pump and output power, was based on the monolith crystal which combines in
one piece a 4mm long cooling undoped YAG crystal, 12mm long active laser part (YAG crystal doped with Nd3+ ions), and 0.7mm long V3+:YAG saturable absorber. The second one was designed to obtain shorter pulse length.
It consists of 4mm long Nd:YAG laser crystal and 0.7mm long V3+:YAG saturable absorber. The diameter of
both crystals was 5 mm. The initial transmission of the V:YAG part (T0 = 85%) and the laser resonator was
the same in both crystals. Laser mirrors were deposited directly onto monolith faces. The output coupler with
reflection 90% for the generated wavelength was placed on the V3+-doped part. The pump mirror (HT@808 nm,
HR@1.3 μm) was placed on opposite monolith face. Both microchip lasers were tested under longitudinal diode
pumping. The pulse length was stable for all regimes for both crystals. For longer crystal it was equal to 6.2 ns,
for the shorter one it was 1.7 ns (FWHM). The wavelength of linearly polarized TEM00 laser mode was fixed
to 1338nm for longer crystal. In case of shorter crystal some instabilities were observed for higher mean pump
power. The pulse energy depends on the mean pump power. For pulsed pumping with low duty factor the output
pulse energy was equal to 131 μJ for longer crystal, and 34 μJ for shorter crystal. This corresponds to peak power
21kW and 20kW, respectively. In CW pump regime the pulse energy was 37 μJ for longer crystal (peak power
6 kW), and 16 μJ for shorter one (peak power 9.4 kW).
Passively mode locked ring vanadate laser pumped by 1 W laser diode was developed. Laser threshold for free running regime was 55 mW, the bidirectional mode locked operation was obtained for incident pump power of only 630 mW. The repetition rate of the laser was 200 MHz, pulse duration 53 ps. New saturable absorber and configuration with two lenses inside the resonator improved stability of mode locking regime. Application of this laser for measuring of small intracavity phase changes is reported.
Q-switched microchip laser emitting radiation at wavelength 1338 nm was designed and realized. This laser was based on monolith crystal which combines in one piece a cooling undoped part (undoped YAG crystal, 4 mm long), active laser part (YAG crystal doped with Nd3+ ions, 12 mm long) and saturable absorber (YAG crystal doped with V3+ ions, 0.7 mm long). The diameter of the diffusion bounded monolith was 5 mm. The initial transmission
of the V:YAG part was 85 %. The microchip resonator consists of
dielectric mirrors directly deposited on the monolith surfaces.
The pump mirror (HT for pump radiation, HR for generated radiation) was placed on the undoped YAG part. The output coupler with reflection 90 % for the generated wavelength was placed on the
V3+-doped part. Q-switched microchip laser was tested
under pulsed, and CW diode pumping. The pulse length it was the
same for all regimes equal to 6.2 ns. The wavelength of linearly polarized laser emission was fixed to 1338 nm. The pulse energy depends on the mean pump power. For pulsed pumping the output pulse energy was stable up to mean pump power 1 W and it was equal to 135 μJ, which corresponds to peak power 22 kW. In CW regime for pumping up to 14 W the pulse energy was stabilized to 37 μJ (peak power 6 kW). The mean output power increased up to 0.4 W only by increase of the generated pulse repetition rate (11 kHz for mean pump power 14 W).
Nd:YAP slab crystal in the form of triangle with the Brewster-angle-cut input faces was used as an active medium for diode-side-pumped laser. Optical pumping was accomplished by a quasi-CW diode ARR18P400 with peak power 400 W closely attached to the active crystal without any coupling optics. The maximum generated output energy in free-running multimode regime was 26 mJ and 17 mJ for wavelengths 1079.6 nm and 1341.6 nm, respectively. Corresponding maximal slope efficiency was 30% and 19%, respectively. The output radiation was horizontally polarized. With the insertion of the LiF:F2- saturable absorber in to the optimized resonator, the pulses with the peak power 30 kW (wavelength 1079.6 nm, length 70 ns FWHM, energy 2 mJ) were obtained at wavelength 1079.6 nm. This system is enough compact and power-full to be useful tools for medical application.
Longitudinally diode pumped monolith Nd:YAG laser operating at wavelength 1.34 μm Q-switched by V:YAG saturable absorber was designed. The monolith combine inside undoped YAG crystal, active YAG crystal doped with Nd3+ ions and YAG crystal doped with
V3+ ions as saturable absorber. The pumping radiation is
directed through the dichroic resonator mirror to the undoped YAG
part which is diffusion bounded to the active Nd:YAG crystal. This
configuration ensures the effective heat removal and lower thermal
distortion of the active crystal part. V:YAG saturable absorber is
diffusion bounded to the un-pumped face of the Nd:YAG section.
Thanks to this configuration the effective heat removal from the
saturable absorber is accomplished, number of reflecting surfaces
and also complete resonator length are reduced. It was proved that
this compact monolith system is more stabile, efficient and easy
to operate in comparison with classical separated laser
configuration.
Nd:YAG and Nd:YAP slab crystal in the form of triangle with the
Brewster-angle-cut polished input faces was used as an active
medium for diode-side-pumped laser. A horizontal projection of the
active medium form is a triangle with 19.22 mm long base, 5 mm
height, and thickness of 4 mm. This active crystal shape is one
from the simplest form which makes possible to realise a slab
side-pumped configuration with a total internal reflection.
Optical pumping was accomplished by a quasi-cw diode ARR18P400
with peak power 400 W closely attached to the active crystal
without any coupling optics. Both material were operated for most
known Nd3+ ion transition 4F3/2→4I11/2 (1 μm) as well as for transition 4F3/2→4I13/2 which leads to the emission at 1.3 μm. The systems were tested in free running and Q switch regime. This system is enough compact to be useful tools for direct medical application.
A specially developed monolith crystal, which combines in one piece cooling undoped part (undoped YAG crystal), active laser part (YAG crystal doped with Nd3+ ions) and saturable absorber (YAG crystal doped with V3+ ions), was used for construction of longitudinally diode pumped Q-switched Nd:YAG laser operating at wavelength 1342 nm. The monolith consists of 4 mm long undoped part bounded to the V:YAG saturable absorber 530 μm thick which gives the initial transmission of saturable absorber 88%. The diameter of whole monolith was 5 mm. This combination of active crystal and saturable absorber allows to realize more compact resonator with the shortest cavity length of 33 mm only. The monolith was mounted in an adjustable water-cooled cupreous ring. Temperature of cooling water was in a range from 12 to 14 °C. As a pumping source the CW-operating laser diode emitting radiation at wavelength 808 nm with the maximum output power 20 W at the end of the fiber (fiber core diameter 400 μm, numerical aperture 0.22) was used. The diode radiation was focused into the active Nd:YAG crystal by two achromatic doublet lenses with the focal length of 75 mm. The measured diameter of pumping beam focus inside the crystal was 360 μm. The resonator of the Nd:YAG laser was formed by a planar dielectric mirror with high transmission for the pumping radiation (T>98%@808nm) together with the high reflectance for the generated radiation (R=100%@1340nm), and by a concave (100mm or 146 mm) dielectric mirror serving as an output coupler. As this coupler a various dielectric reflectors (with the reflectivity from 82% up to 94%) was used with the reason to obtain the shortest giant pulse with the maximum power. As the optimal, the stable CW Q-switched output at wavelength 1342 nm with length of pulses 11 ns with repetition rate 6.4kHz and peak power 6.1kW, was obtained.
Crystals of Yttrium-Aluminum Garnet (YAG) doped with three-valence vanadium V3+ in tetrahedral position suggest e_cient passive absorber for lasers operating in range 1100 { 1400 nm. V3+:YAG is a hard and durable material which has good thermal conductivity, is chemically stable, and capable of being grown to very high quality. This solid state saturable absorber has high damage threshold and it can operate without optical degradation. The Q-switching and mode-locking has been obtained with a number of active media such as Nd:YAG, Nd:KGW, Nd:YVO4 under ash-lamp and laser diode pumping in last ten years. We reported output improvement of the Nd:YAP (Yttrium-Aluminum Perovskite) ash-lamp pumped laser passively mode-locked with the V3+:YAG crystal. Laser has been operating at wavelength 1340 nm. Special _nishing of all surfaces was used to avoid operation at 1080 nm. Low-level transmission of V3+:YAG crystal was 28%. The optimal output coupler reectivity was 60%. With pumping energy 100 J stable generation of a single train of pulses was achieved with repetition rate 5 Hz. Length of the pulse train was 17 ns (FWHM); a single pulse was shorter than 1 ns. Energy at whole train of pulses 53mJ was obtained what corresponds to peak power 2MW.
V:YAG saturable absorber was used for efficient Q-switching and mode-locking of Nd:YAG and Nd:YAP flash-lamp or diode pumped lasers operating in 1.3 mm region. Crystals of Yttrium-Aluminum Garnet (YAG) doped with three-valence vanadium V3+ in tetrahedral position (V:YAG) were grown using of Czochralski method in reducing protective atmosphere. High purity oxides were used for crystal growth (Y2O3 (5N), Al2O3 (5N), V2O5 (4N)). Concentration of V2O5 in the melt reached up to 1 wt. %. Discs of the diameter 5 or 10 mm and of various thickness were machined from grown V:YAG crystals. The discs were both sides polished and AR coated so that minimum reflectivity at 1.08 and 1.34 microns was reached. The initial transmission of the saturable absorber was dependent on the sample's thickness and its annealing process. We report stability improvement of passively mode-locked (by these V:YAG crystals) Nd:YAP flash-lamp pumped lasers. The maximum output energy 53 mJ at wavelength 1340 nm was obtained for Nd:YAP flash-lamp pumped laser operating at repetition rate 5 Hz. Mode-locked train envelope width was measured to be 22 ns (FWHM). Individual pulses inside the train were shorter than 1 ns. Also results with composite Nd:YAG rod Q-switched by V:YAG crystal and with Nd:YAG/V:YAG monolith rod under CW longitudinal diode pumping was obtained and compared. These laser systems represent new powerfull sources in the near infrared region.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.