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Stimulated Raman scattering (SRS) of picosecond pulses is investigated in a new crystal SrWO4. The second harmonic generation of a mode-locked Nd:YAG laser system is used as the pump source. In an external single-pass configuration, the SRS thresholds for the first to the fourth Stokes lines are measured. For the first Stokes line, the steady-state gain coefficient of the SrWO4 crystal is calculated to be 15.96 cm/GW. In our experiment, as many as five Stokes lines (559.23 nm, 589.61 nm, 623.49 nm, 661.50 nm, 704.44 nm) and three anti-Stokes lines (506.97 nm, 484.34 nm, 463.65 nm) are observed, and the total conversion efficiency is as high as 62%.

We report an efficient pumping scheme which involves a direct excitation of the upper lasing level of a four-level laser in a Nd-doped Ca3(NbGa)2-xGa3O12 (Nd:CNGG) by using a tunable Tr.sapphire, 700–920 nm, cw pump source. The slope efficiency is improved from 10.5% of the traditional band pumping at 808nm to 21.8% of the direct pumping at 882 nm. The influence of pumping wavelength on lasing is discussed. We present a scheme of double pumping for lasing.

Using an external couple cavity and a pump beam compression system, efficient 1.5 μm eye-safe Raman laser is obtained based on BaWO4 crystal. The largest output energy is 8.5mJ, corresponding to an electric-optical conversion efficiency of 47%.

Yb:GdYAl3(BO3)4(Yb:GdYAB) is investigated as a new laser crystal for potential applications in self-frequency doubling. The emission and absorption properties of Yb:GdYAB crystal are studied, and the emission decay times of the upper laser level are measured. The emission cross sections are evaluated using the absorption cross section and principle of reciprocity. The other laser performance parameters, such as the minimum inversion fraction βmin, pump saturation intensity Isat and minimum pump intensity Imin, are also calculated. The results are discussed in the framework of requirements for an effective diode-pumped Yb3+ laser system. Yb:GdYAB is expected to exhibit the most useful laser properties and to be superior to Yb:YAB crystal that has been excellent self-frequency-doubling crystal at present in many key spectroscopic parameter values.

A simplified n- ZnO/ p- Si heterojunction has been prepared by growing n- type ZnO rods on p- type silicon wafer through the chemical vapour deposition method. The reflectance spectrum of the sample shows an independent absorption peak at 384 nm, which may be originated from the bound states at the junction. In the photoluminescence spectrum a new emission band is shown at 393 nm, besides the bandedge emission at 380 nm. The electroluminescence spectrum of the n- ZnO/ p- Si heterojunction shows a stable yellow luminescence band centred at 560 nm, which can be attributed to the emission from trapped states. Another kind of discrete ZnO rod has also been prepared on such silicon wafer and is encapsulated with carbonated polystyrene for electroluminescence detection. This composite structure shows a weak ultraviolet electroluminescence band at 395 nm and a yellow electroluminescence band. These data prove that surface modification which blocks the transverse movement of carriers between neighbouring nanorods plays important roles in the ultraviolet emission of ZnO nanorods. These findings are vital for future display device design.

A compact laser diode-pumped solid-state Nd:LuVO4 acousto-optic Q-switched laser is demonstrated at 916 nm of a quasi-three level for the first time. A pulse width of 130 ns is observed when the pulse-repetition frequency is 10 kHz. The laser experiment shows that the Nd:LuVO4 crystal can be used for efficient diode-pumped Q-switched lasers.

We report the compact diode-pumped continuous-wave (CW) Nd:LuVO4 lasers operated at 916 nm and 458 nm for the first time. The maximum output power of 780 mW at 916 nm laser is obtained with a slope efficiency of 9.3%. We generate 50 mW of 458 nm blue laser employing a type-I critical phase-matched LBO crystal.

A planar optical waveguide is formed in monoclinic double rare-earth-tungstate laser crystal Yb:KLu(WO4)2 by 6.0 MeV oxygen ion implantation with a dose of 2×1015 ions/cm2 at room temperature. Subsequently, annealing at 300°C for an hour in air is performed on the sample to decrease colour centres to improve the thermal stability of the waveguide. The refractive index profiles of the waveguide are reconstructed by an effective refractive index method. Dark modes of the waveguide are observed at wavelengths of 633 nm and 1539 nm. TRIM'98 is used to simulate the damage profile caused by the implantation process. It is found that the refractive index change may be mainly due to the damage induced by the nuclear energy loss.

Considering that KBe2BO3F2 (KBBF) is an outstanding deep ultraviolet crystal which can generate the shortest wavelengths in second harmonic generation and sum-frequency generation, we report the determination of the nonlinear optical coefficients of the KBBF crystal. The d11 coefficient was determined to be 0.49 pm/V by the Maker fringes method at the wavelength 1064 nm, which is in agreement well with the theoretical value.

The nonlinear-optical coefficients of RCOB (R = Gd, Y) crystals are measured. The spatial distribution of deff (effective nonlinear-optical coefficient) is subsequently determined. Our experiments show that the maximum deff occurs at the second quadrant. The second-harmonic generation efficiency reaches 48% for a 6 mm long, (113.2°, 47.4°)-cut GdCOB, and 41.5% for a 5mm long, (113°, 36.5°)-cut YCOB, respectively. The intracavity frequency doubling of GdCOB is reported for the first time.

A self-starting mode-locked femtosecond laser is accomplished with an oxoborate self-frequency doubling crystal Yb:YCa4O(BO3)3 (Yb:YCOB) as the gain medium and a semiconductor mirror as the saturable absorber. Pumped by a 976-nm fiber-coupled diode laser with 50-μm core diameter, stable mode-locked laser pulses up to 430 mW were obtained at a repetition rate of 83.61 MHz under 5-W pump power. The autocorrelation measurement shows that the pulse duration is as short as 150 fs by assuming the sech2 pulse shape at a central wavelength of 1048 nm. This work has demonstrated a compact and reliable femtosecond laser source for prospective low-cost applications.

The photorefractive properties of Cu doped KTa1-xNbxO3 have been studied by using two-wave mixing method. The diffraction efficiency reaches as high as 52% under an electric field. The dependences of diffraction efficiency on interference angles and applied fields have been studied. The maximum light induced index change is found to be 2.33 × 10-5 and the photorefraction sensitivity calculated is 5 × 10-6 cm2/J. Experimental results demonstrate that electrons are the dominant charge carriers.

We demonstrate a passively cw mode-locked Nd:LuVO4 laser operating on the quasi-three-level at 916 nm with a Z-folded resonator. Using a semiconductor saturable absorber mirror (SESAM) as the passive mode-locking device, we achieve stable cw mode locking with 6.7 ps pulse duration at repetition rate of 133MHz and 88mW average output power under the pump power of 17.1 W.

We report a diode stack end-pumped Nd:GdVO4 slab laser with a near-diffraction-limited beam. The output power of 45.8 W at 1064 nm is obtained under the pumping power of 147 W, with the optical-optical conversion efficiency of 31.2%, and the slope efficiency is 39.6%.

A stable all-normal-dispersion dissipative-soliton mode-locked laser is demonstrated with a Yb3+-doped large-mode-area double-clad gain fiber, and nonlinear polarization evolution and spectral filtering composed of a grating and an aperture are exploited to produce sufficient amplitude modulation to shape pulses of this laser. The laser generates chirped pulses at a 76.6 MHz repetition rate, with an average power of 6.3 W, and a single pulse energy of 82 nJ. Pulse duration of the direct output pulse is 1.33 ps and it can be dechirped to 377 fs after externally compressed. By adjusting the grating, the central wavelength of the output pulses can also be tuned from 1025 nm to 1078 nm.

The ultraviolet beam at 266 nm was obtained by fourth harmonic generation of 1064 nm Nd:YAG laser radiation through a nonlinear crystal K2Al2B2O7 (KABO). The fundamental frequency of a flash-lamp pumped Nd:YAG laser was doubled in a β-Ba2B2O4 crystal to generate a second harmonic output at the wavelength of 532 nm, and then doubled again in the KABO crystal to generate the fourth harmonic output at 266 nm. The optical conversion efficiency from 532 to 266 nm was investigated for the first time, and 13% was achieved.

The room-temperature polarized absorption and emission spectra of Yb doped mixed vanadates Yb 0.005 :Y 0.298 Gd 0.697 VO 4 , Yb 0.007 :Y 0.407 Gd 0.586 VO 4 , and Yb 0.009 :Y 0.575 Gd 0.416 VO 4 have been studied. The results show that the strongest absorption and emission, occurring at wavelength of 985 nm, correspond to the π polarization, depending on the composition the maximum absorption cross section ranges from 4.8 to 8.5×10 -20 cm 2 , with bandwidths of 9.5—9.9 nm, whereas the maximum stimulated emission cross section varies in the range of 5.8—10.3×10 -20 cm 2 . Continuous-wave laser operation has been realized at room temperature with the mixed crystals through longitudinal pumping with a diode laser. It was found that the laser oscillation behavior differs significantly from one mixed crystal to another:in the case of T =2% ( T is the output coupling of the resonator), the coexistence and switching of σ, π polarization states occur on reducing the pump power in the laser oscillation of Yb 0.005 :Y 0.298 Gd 0.697 VO 4 and Yb 0.009 :Y 0.575 Gd 0.416 VO 4 , while the laser oscillation of Yb 0.007 :Y 0.407 Gd 0.586 VO 4 is capable of maintaining its π polarization state. In the case of T =5%, however, the laser oscillation generated with Yb 0.009 :Y 0.575 Gd 0.416 VO 4 is purely σ-polarized, whereas the laser behavior of Yb 0.005 :Y 0.298 Gd 0.697 VO 4 is similar to that exhibited in the case of T =2%.

The rare-earth ions (Yb3+, Tm3+) and Li+, Bi3+ ions doped GdCa4O(BO3)3 crystals were grown using the Czochralski pulling method. The second-harmonic generation conversion efficiencies of the GdCOB:Yb and GdCOB:Tm crystals are 31.3% and 33.3%, respectively, while the undoped GdCOB crystal is 27.9%. The conversion efficiencies of Yb3+, Tm3+ doped GdCOB are improved by 12% and 19%, respectively, compared to that of the undoped one. The conversion efficiencies of Li+, Bi3+ doped GdCOB crystals are 33% and 38.3%, which are improved by 15% and 37% as compared to that of the undoped crystal. The results are discussed using the anion group theory.

We have studied the effect of optical bistability exhibited in the laser oscillation of Yb:LuVO4, Yb:YVO4, and Yb:GdVO4, the three Yb doped vanadate crystals. The bistability range can be in excess of 1 W in terms of the pump power absorbed by the crystal. At the high-power-end side of the bistability region, i.e., the upper threshold for laser oscillation, discontinuous growing in the output power takes place, along with large fluctuations in the laser intensity occurring on sub-millisecond time scale. It is found that the bistability effect is affected significantly by the output coupling of the resonator, the crystal thickness, and the thermal effect existing in the crystal.

Large sized and optical quality GdCa4O(BO3)3 (GdCOB) crystal with calcium partially substituted by strontium (Sr) ions was grown for the first time. The x-ray powder diffraction shows that the Sr ion has an effect on the cell parameters of the GdCOB crystal. Second-harmonic generation (SHG) experiments were performed on the Sr:GdCOB and GdCOB crystals along the spatial phase-matching direction. The results show that the cw green laser output power is 1.04 W when the laser diode pump power is 10 W in the Nd:YVO4/Sr:GdCOB intracavity laser. Considering the slope efficiency of Nd:YVO4 and the fundamental laser in cavity, the intracavity SHG conversion efficiency of the GdCOB crystal is 21% while it is 24% for the Sr:GdCOB crystal, the SHG conversion efficiency is improved by 14%. The effect of the Sr ions on the nonlinearity of the GdCOB crystal is also discussed by using the anion group theory. PACS: 42. 65. Ky, 78. 20. -e, 78. 55. Hx

We conducted an investigation into the polarized absorption and emission spectra, the absorption for unpolarized pump light, and the continuous-wave (cw) laser properties of the Yb:KLu(WO4)2 crystal. The low symmetry of the crystal leads to strong anisotropy in the crystal spectroscopy; the strongest absorption and emission occur in the polarization direction parallel to the Nm principal axis. The Ng-cut crystal has highest absorption efficiency for unpolarized pump light and largest potential for generating laser output power. With 11 W of cw output power produced by using a 2 mm thick crystal, the optical-to-optical conversion and slope efficiencies amount to 68% and 80%, respectively, with respect to the absorbed pump power.

With an ultra-cavity single-pass configuration, the stimulated Raman scattering (SRS) of a new crystal YbVO4 was investigated. When the pump source was a 532 nm pico-seconds laser, as many as three Stokes lines (558.47, 587.92 and 620.67 nm) and one anti-Stokes line (507.58 nm) were observed. The steady-state Raman gain coefficient for the first Stokes line was measured to be 17.8±0.2 cm/GW, and the total conversion efficiency reached 37%. For the first time, the SRS of YbVO4 crystal for 355 nm pump laser was realized. The first Stokes line (366.11 nm) was observed, and according to the pumping thresholds, the steady-state Raman gain coefficient was determined to be 29.0±0.3 cm/GW.

The electronic mechanism of Ca2+ doped sodium barium niobate crystals and the change in induced photorefractive properties are studied based on its transmission properties. Curves of the refractive index changing with time are plotted using Michelson interferometry. Experimental results show that proper Ca2+doping in sodium barium niobate crystals can improve the photorefractive properties effectively.

A new LD end pumped Nd：LuVO4 microchip laser was reported for the first time. Study of laser properties was carried out on the effects of different Nd3+ doped concentration，different cavity length and different 1064nm transmission. The relationship between the maximum output power and LD performance temperature was measured at different pump power. 923mW of continuous output at 1064nm with TEM00 mode was obtained at 2W pump power，the pump threshold being 48mW. The slope efficiency was 52%，and increased to 59% when the microchip was cooled.

In this paper, the interaction between the optical activity and electr o_optic effect has been studied, and its influence on the electro_optic Q s witcher made of the optically active crystal has also been studied.

For BiB3O6(BIBO) crystals the refractive index on the main optical axis was measured. A systematic research was performed on the frequency-doubling property of the BIBO crystal. When the fundamental light was supplied by a Nd:YAG laser (λ=1064nm), the largest effective nonlinear optical coefficient was found in th e Type-Ⅰ phase-matching direction (168.9°, 90°). We measured the angular acce ptance, temperature acceptance, laser damage threshold, and the ultra-cavity as well as the intro-cavity frequency-doubling characteristics of the BIBO crystal. In our experiments, the largest ultra-cavity frequency-doubling conversion effi ciency was 68%, and the intro-cavity frequency doubling output power reached 1.0 6W.

A special prism coupling technique with the KBe2BO3F2 crystal is adopted to produce deep ultraviolet light including the fourth harmonic from an Nd:YAG laser, for which a conversion efficiency as high as 10% has been obtained.

Using the Sellmeier equations of GdCOB and YCOB, we determined the wavelength range in which non-critical phase matching in GdxY1-xCOB can be realized. Using a 704-5 type optical parametric amplifier, we measured the non-critical phase-matching wavelengths in several GdxY1-xCOB crystals with different compositional parameter x.

The Raman spectra of KTP single crystal that is an excellent material applicable to the nonlinear optical devices have been obtained. And its features are discussed in some detail in terms of group the-ory, lattice dynamics and ligand field theory.

The photorefractive Fe-dopoed KTa 1-x Nb x O 3 (KTN) with a Curie point near room temperature has been topographically studied by Beijing synchrotron radiation white-beam X-ray source. Besides inclusions and the [010] oriented growth bands present in KTN, a set of domains perpendicular to the growth bands is shown, the latter is found to disobey the vanishing rule of planar defects, and to be revealed only by X-ray anomalous scattering. A striking wavelength dependence of the domain contrast is shown by tuning the synchrotron radiation, and the contrast reversal of the domains is demonstrated in antiparallel reflections. The domains are ascertained to be 1800 ones. The origins of formation of the domains and the growth features in KTN are outlined.

EPR spectra of V4+-doped single crystal (V4+/KTP) were observed in X band at room temperature. The analysis on the spectra shows that the V4+ ions may occupy two kinds of crystallographically diffrent sites, each kind of sites contains four magnetically nonequivalent but crystallographically equivalent sites. The angular varitions of EPR hyperfine lines were measured with the external magnetic field in three mutually perpendicular planes. The principal values and direction cosines of the principal axes of the g and A tensors, were computed by a least-squares fitting procedure. These main results reveal that the V enters the lattice to substitute for the Ti ion of KTP to form V site with a tetragonally distorted octahetral symmetry. The orientations of all eight Ti ion sites substituted in an unit cell of KTP have been determined.

Total electrooptic coefficients of KTiOPO4 crystal have been measured by interferometric method. The results obtained are:γ13 = 7.9, γ23= 11.3, γ33= 22.7, γ51=10.6 and γ42= 6.2(×10-10cm/V).