We identified eight nonlinear crystals enabling THz emission from quadratic phase-matched Difference-Frequency-Generation: YCOB, BNA, LBO, CSP, AGS, CdSe, ZnO and GaP. For all these crystals, we performed Time-Domain Spectroscopy in the same conditions to determine their absorption spectra in polarized light as well as their principal refractive indices as a function of wavelength in the 0.5-2.0 THz range. By combining previous data with the Sellmeier equations valid in their visible and infrared transparency ranges, we calculated the coherence length of Difference-Frequency-Generation associated to all possible configurations of polarization and found interesting and complementary phase-matching conditions in the eight studied crystals.
We demonstrate a passively Q-switched Yb3+-dopedScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4 μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics.
In this paper, we report an abnormal laser deflection phenomena based on quadratic electro-optic effect in copper doped KTN crystal. Cu:KTa0.62Nb0.38O3 block with size a×b×c = 2.8mm×2.6mm×12.5mm was used as beam deflection element. 75mrad beam deflection angle were observed under 1KV voltage when the laser beam across the c direction of the sample at room temperature. The special features of our experiment are that the direction of laser beam deflect perpendicular to the electric field direction, and the angular size and direction of the deflection beam remain unchanged when the electric field direction reverse. We believe that the interaction of graded refractivity and electro-optic effect leads to these special features. Besides of the special deflection mode, the deflection efficiency of our experiment also reached the world advanced level.
A new series Er:LuxGd1-xVO4 (x=0.1,0.24,0.48,0.57,0.79 and 0.9)mixed laser crystals have been successfully grown by the Czochralski method with 1% Er3+ concentration.The thermal properties of Er:LuxGd1-xVO4crystals series crystals were investigated systematically, including the thermal expansion, specific heat, thermal diffusion coefficients, and thermal conductivities. The anisotropy and variation of the thermal properties with the component x were also achieved and discussed based on their structure. All the results showed that this mixed crystals should have promising applications in the moderate-power lasers.
Nd3PO7 was synthesized by solid state reaction techniques under high temperature in air atmosphere for the first time, the crystal phase of Nd3PO7 was investigated by X-ray powder diffraction and scanning electron microscopy, the results show that Nd3PO7 is monoclinic phase; the Nd: P: O = 3:1:7; Infrared spectroscopic study was used to obtain further structural information about the nature of bonding in Nd3PO7. Emission spectra of Nd3PO7 were investigated at room temperature using a fluorescence spectrometer in the visible portion of the spectrum. Excellent emission was observed at 441 nm when Nd3PO7 excited at 325 nm wavelength, which was assigned to the 4G11/2-4I9/2 transition of Nd3+ ions. All the investigated suggestions that Nd3PO7 is a good phosphor candidate applied in fluorescent materials.
In this paper, LaxNd1-xPO4(x=0, 0.5, 0.8) series crystals with high Nd-concentration were grown through a seed-inducing method using Li2CO3-2MoO3 as a flux, and some factors influencing the quality of crystals were also discussed. The IR, absorption and fluorescence spectra of La0.5Nd0.5PO4 crystals at room temperature were measured. High temperature X-ray diffraction was conducted to investigate the thermal expansion behavior of NdPO4 crystals in the temperature range from 25°C to 900°C. Abnormal diffraction peaks shifts were observed along the (200) and (020) direction. The results indicate that as temperature increased, the crystal in the (200) and (020) direction contracted (from 25 °C to 700 °C) at first, and then expanded (from 700°C to 900°C). The mechanism responsible for the abnormal thermal expansion in NdPO4 was attributed to the existence of rigid unit modes (RUM).
A high power passive Q-switched laser and a continuous-wave (CW) green laser both with a neodymium-doped yttrium aluminum garnet (Nd:YAG) ceramic as the laser material have been demonstrated. Two Cr4+:YAG crystals with 73.9% and 79.6% initial transmission at 1064 nm have been used as saturable absorbers. In Q-switched regime the laser generated up to 209 μJ, 4.5 ns pulses, which corresponds to a peak power of 46.8 kW. In CW regime at 1064 nm the laser generated 11.3 W of output power at a pump power of 21.6 W, corresponding to an optical-optical conversion efficiency of 52.3%. By using a type-II cut KTP crystal, the CW frequency-doubled operation of Nd:YAG ceramic was achieved. The maximum output power of 1.86 W at 532 nm has been obtained. The one-dimensional intensity distribution of the green beam cross-section was observed to be Gaussian. When the output power was 1 W, the M2 factor was measured to be 1.7.
Disordered crystals combining the advantages of both crystals and glasses are very interesting for applications in tunable,
Q-switched, and mode-locked solid-state lasers. Calcium niobium gallium garnet, Ca3(NbGa)2-xGa3O12 (CNGG), has a thermal conductivity of 4.7 Wm-1K-1 which is about 40% of that of undoped YAG and much higher than for glasses. It has a number of non-equivalent lattice sites to accommodate trivalent dopant ions, providing an effective mechanism for substantial inhomogeneous line broadening. For the Yb ion, owing to its intrinsic broad absorption and emission spectra,
this line broadening effect is not so remarkable as for Nd or Tm but still the main emission band around 1028 nm of
Yb:CNGG, with a FWHM of 21 nm is two times wider than the corresponding line (<10 nm) in Yb:YAG. Here, we
report efficient laser operation achieved with Yb:CNGG at room temperature in cw as well as Q-switched regimes,
revealing interesting characteristics of the laser oscillation. 2.0 W of cw output power were produced at an absorbed
pump power of 6.32 W, leading to an optical-to-optical efficiency of 32% and a slope efficiency of 40%. The laser
oscillation of the isotropic crystal was actually linearly polarized as a result of the stress-induced birefringence. Two
orthogonal polarization states oscillated simultaneously at high pump power levels. Passive Q-switching by a Cr4+:YAG
saturable absorber produced 1.35 W of average output power at 1033 nm at a pulse repetition rate of 16.7 kHz. The laser
pulse energy, duration, and peak power were 81 μJ, 25 ns, and 3.24 kW, respectively.
GdCa4O(BO3)3 (GdCOB) is a promising host material for the trivalent Yb-ion with large splitting (>1000 cm-1) of the ground state (2F7/2) which facilitates efficient laser operation at room temperature. There have been a number of investigations in the continuous-wave (cw) regime, however, most of the previous studies ignored the issue of crystal orientation. GdCOB is a low symmetry biaxial crystal (point group m) and the absorption and emission spectra of Yb
exhibit strong anisotropy. Here we report our experimental results with Yb:GdCOB crystals cut along the three principal
optical axes under high-power unpolarized diode pumping in a simple plano-concave cavity. Our study reveals clearly
significant anisotropy of the laser performance of Yb:GdCOB. For the y-cut crystal, polarized laser oscillation along the
x- or z-axes is feasible, depending on the output coupling (T) utilized; with a specific T = 3% the two orthogonal
polarization states exist simultaneously at different emission wavelengths. The laser oscillation obtained with the x- and
z-cut crystals is polarized along the z- and x-axes, respectively, independent of T and the power level. Despite its complex output-coupling-dependent nature of laser oscillation, the y-cut crystal turns out to be the most promising for efficient high-power operation. A cw output power of 7.35 W at 1083-1085 nm polarized along the x-axis is obtained at room temperature, with an optical-to-optical efficiency of 63% and slope efficiency as high as 84%.
We report a new type of high-speed electro-optic (E-O) beam scanner based on Potassium Tantalate Niobate
(KTN) crystal. It has larger scanning angle, better angular resolution, and lower driving voltage comparing to the
traditional E-O crystal beam scanner. Compared to conventional moving mirrors such as servo-controlled mirrors and
galvanic mirrors, the demonstrated E-O beam scanner can improve the response time by 100 times. The presented
device has many other unique features such as light weight, small dimension, low power consumption, and no-moving
components particularly suitable for airborne and space-borne applications.
The first demonstration of a pulsed Nd:YCOB laser at 1060 nm is reported, with results for both gain switching and Qswitching
presented. Active Q-switching is achieved using the spinning disc technique pulses of 50 ns duration with
pulse energies up to 0.6 mJ are obtained. Optimisation is performed for both pulse energy and slope efficiency of the
laser. A Q-switched slope efficiency of 56% is achieved.
Monoclinic potassium double tungstates are biaxial laser materials characterized by strong anisotropy of the spectroscopic properties. KLu(WO4)2 is the most attractive of them in the case of Yb-doping because of the close ionic radii of Yb and Lu. In this work we compare crystals of equal dimensions and doping level but different cuts, under the same pumping conditions. Special emphasis is placed on the polarization behavior. We present substantial power scaling with KLu(WO4)2 in the continuous-wave regime by longitudinal fiber-coupled diode laser pumping. Slope efficiency of roughly 80% is achieved while the naturally selected laser polarization is parallel either to the Np or Nm principal optical axes. A maximum output power of 11.0 W was produced from a 2 mm thick uncoated crystal with Ng-cut, the corresponding optical-to-optical efficiency was 68%.
The tetragonal double tungstates NaGd(WO4)2 and NaY(WO4)2 are uniaxial crystals which can be grown from the melt
by the Czochralski method and exhibit disordered crystalline structure. The structural disorder leads to additional
inhomogeneous broadening of the spectral features of the doping rare-earth ions. We report on passive Q-switching of
Yb:NaGd(WO4)2 and Yb:NaY(WO4)2 lasers operating near 1 μm using a Cr4+:YAG saturable absorber in a simple,
diode end-pumped plano-concave resonator. With both crystals average powers of roughly 2 W were obtained for pulse
durations of ≈30 ns and single pulse energy of ≈150 μJ at kilohertz repetition rates (roughly from 1 kHz to above
10 kHz). The maximum slope efficiency achieved in the Q-switched mode of operation was 40%.
We studied several crystals of Yb-doped LuVO4 with different orientations (a-cut and c-cut) in order to evaluate the
potential of this new laser material for high power continuous-wave operation using simple hemispherical cavities,
longitudinally pumped by a fiber coupled diode laser. We achieved substantial improvement with respect to previous
results in terms of output power and slope efficiency. The highest output power and optical efficiency were obtained for
the &pgr;-polarization using a-cut samples. Bistability of the input-output power characteristics in terms of a hysteresis loop
was also observed. Significant intensity fluctuations were found existing in a small operational region near the critical
point (up-threshold) of the bistability region. The heating of the crystal is reduced in the lasing state when stimulated
emission keeps the part of the radiative relaxation high in comparison to the nonradiative relaxation processes.
As self-frequency-doubled (SFD) lasers are potentially more compact and less costly, the novel high efficient SFD lasers
attract great interest. Here we report the spectroscopic properties under room temperature of a new self-frequency-double
Yb3+ doped Gd0.2Y0.75(BO3)4 (Yb:GdYAB) single crystal grown in Shandong University. Both foundation and
self-double-frequency continuous-wave laser were operated with a high-power diode. A foundation laser slope
efficiency of 82% with respect to the absorbed 975 nm pump power of 2.62 W was obtained. The center wavelength at
1040nm was generated and the laser wavelength could be tuned from 1020 to 1064 nm. And thus, the broadly emission
spectra was advantageous for the production of short-pulse diode-pumped solid state lasers. Self-double-frequency green
light was also obtained under pump power of only 274mW with a flat-concave cavity. The maximal output power was
330mW when pumped power was 2.62 W. A diode-to-green optical conversion efficient of 12.6% was achieved. The
results demonstrated that the Yb:GdYAB crystals are potential candidates for efficient microchip both 1 μm and visible
laser media.
The absorption spectrum from 300 to 1000 nm and emission spectrum from 960 to 1450 nm of Nd:LuVO4 crystal were measured. A LD-end-pumped passive Q-switched Nd:LuVO4 laser was reported. With a Cr4+:YAG crystal as the saturable absorber, the maximum average output power was measured to be 4.58 W, and the corresponding optical conversion efficiency was 24.0 %, with the pulse energy, peak power, and pulse width being 36.6 μJ, 436.2 W, and 84 ns, respectively.
All-solid-state laser devices operating in the 1.5 - 1.6 μm wavelength range have many practical applications. The most notable of these is their use in optical telecommunications, but the current research drive is to increase the output power from high beam quality, solid-state devices for eye-safe applications such as laser range finding and target acquisition, remote sensing of trace elements in air, light detecting and ranging, medicine, metrology and atmospheric phenomena such as measurements of wind shear.
Yb3+ ions are co-doped into the host material to improve the pumping efficiency by taking advantage of commercial InGaAs diode lasers emitting at 980 nm. The absorbed pump is then non-radiative transferred to the Er3+ ions, and rapidly decaying to the 4I13/2 upper-laser level. Laser operation in Er,Yb co-doped systems has been dominated by glass hosts (in particular, phosphate) with attempts in crystalline materials yielding disappointing results despite their superior mechanical and thermal properties.
In this paper we will present efficient diode-pumped laser operation of the crystalline host material Er,Yb:YCOB at 1.55 μm. By studying the energy transfer mechanisms of this material, we have identified the optimum dopant concentrations and 250 mW of continuous wave (cw) output in TEM00 transverse mode has been obtained with a 2mm crystal in an hemispherical cavity. Also, >150 mW cw has been obtained in a flat-flat cavity arrangement. The output coupling in each case was 1%. The slope efficiency of the laser was 21.9%.
Doping ZnO and Ga2O3 in LiNbO3 crystal, the Zn:Ga:LiNbO3 was grown by Czochralski method. The IR transmission spectra and the photon damage resistance ability of the LiNbO3 and Zn:Ga:LiNbO3 crystal were measured. The proton exchange technology was used to make the LiNbO3 and Zn:Ga:LiNbO3 crystal waveguide substrates. The m-line method was taken to study the photo damage of waveguide substrate. We observed that the threshold of Zn:Ga:LiNbO3 is above two magnitude higher than that of Mg:LiNbO3. Zn:Ga:LiNbO3 crystal is better performance than LiNbO3 crystal.
The polarized absorption spectra of Nd:YCOB crystal was measured. Optical properties were studied via Judd-Ofelt analysis. The line strength, intensity parameters, radiative transition rates, life time and branching ratios were calculated. The results were discussed. Using an Ar+ laser pumped CW tunable Ti:sapphire as a pumping source, the self-frequency doubling laser operation was successfully investigated. The lasing threshold is measured to be 2 mW, the optical-optical conversion efficiency is about 3.7%. To our knowledge, this is the lowest threshold and highest conversion efficiency reported so far.
We have developed a simple method for measuring damage threshold of KTP crystal for CW irradiation using an Argon laser. The experimental results show that there are two types of optical damage in KTP crystal depending on the polarization of the incident laser beam. One type of optical damage corresponds to gray tracks that will be formed when the polarization is perpendicular to the z-axis. Another one is invisible damage that will be formed when the polarization is parallel to the z-axis. In addition, we also observed photorefractive two-wave mixing in KTP crystal under each of the above two polarization states. Our experimental results imply that there exists charge drift during the process of optical damage at both of these polarization states, but the mechanisms are different at these two orthogonal polarization states. After analyses, we believe the first type of damage is due to the formation of Ti3+ centers and the second one is due to the drift of K+ ions.
We have demonstrated a laser diode pumped Nd:YVO4 laser that produced 273 mW cw output at 671 nm with a KTP crystal as intracavity frequency doubler. The optical-optical conversion efficiency of the all-solid-state red laser was 5.1%.
Crystal growth of KTiOPO4(KTP) family with flux method has been summarized. The results of defect observation with synchrotron radiation topography and other methods have been reported. It is shown that KTP crystal is of high-quality and there exist different kinds of defect such as growth striations, multiple domains in doped KTP and KTA crystals. The observation and discussion about the bicrystal of KTP family crystal have been mentioned in the paper. SHG and SFG measurements indicated that KTP family crystals investigated have excellent nonlinear optical properties.
Using a KTP crystal in the size of 6 .5x9x20 mm (length) , cut at 0 = 57° in X-Z plane, and with the second harmonic (532 nm) of the repetition rate mode-locked Nd:YAG laser light as the pumping source (pulse duration of 40 ps), tunable parametric laser emission from 630 nm to 3420 nm (in addition to those in the vicinity of degeneracy point) has been obtained by angle tuning for phase-matched type II OPG process. The maximum energy conversion efficiency is 30%, the peak power at the signal wave of 1300 nm is 20 NW.
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