Bismuth triborate (BiB3O6) optical parametric oscillators

We report the phase matching of parametric frequency conversion in the nonlinear material BiB₃O₆ (BiBO) and on an investigation of optical parametric oscillators (OPOs) of this new crystal. Based on the calculation of collinear type I and type II phase matching within the refractive-index planes, the most favorable directions for phase matching are identified for OPOs pumped by the fundamental or the harmonics of 1064-nm Nd-doped lasers. Based on these results, pulsed 532-nm-pumped ns OPOs are realized. The pump source is either a Q-switched high repetition rate (10 kHz) Nd:YVO₄ laser (with a pulse energy of 24 J) or a low repetition rate (10 Hz), high pulse energy (120 mJ) Nd:YAG laser system. The BiBO OPO pumped by the Nd:YVO₄ laser showed a very low threshold of 0.047 J/cm². At an average pump power of 2.4 W the total OPO output power was 630 mW. By changing the phase-matching angle within the yz plane from 0 to 11.6° the signal wavelength was tuned from 735 nm to 970 nm, while the spectral width changed from 0.2 nm to 1.4 nm. By pumping the OPO with the Nd:YAG laser, the OPO had a threshold of 0.12 J/cm², a steep slope (59%) and a high total efficiency (of up to 48%). Due to divergence broadening the spectral width changes from 8.5 nm at 800 nm to 70 nm near degeneracy. The properties of BiBO determined from the experimental results are compared with those of well-known nonlinear materials such as BBO, LBO and KTP. PACS 42.65.-k; 42.65.Yj; 42.70.-a; 42.70.Mp     

Generation of UV radiation at 335.5 nm based on frequency-quadrupling of a diode-pumped Nd:YVO4 laser

The generation of ultraviolet （UV） light at 335.5 nm based on frequency quadrupling of a diode-end- pumped Q-switched Nd：YVO4 laser at 1342 nm was demonstrated. KTP crystal was used for generation of wavelength of 671 nm by intracavity doubling and LBO （BBO） crystal was exploited for the subsequent external fourth harmonic generation （FHG）. With 6.3-W absorbed pump power and 10-kHz frequency repetition rate, the UV output power of 35 and 63 mW were obtained by using LBO and BBO as frequency quadrupling nonlinear crystals, respectively. The experimental results show that the conversion efficiency （red-UV） of 6.4% for BBO crystal is higher than that of 3.5% for LBO crystal, but the UV beam quality obtained by LBO crystal is better than by BBO crystal.     

Non-linear crystals for tunable coherent sources

High-efficiency non-linear crystals suitable for the generation of coherent sources ranging from the deep ultraviolet to mid-infrared (0.16 to 5 µm) are explored. The key parameters for frequency conversion techniques (second-harmonic-generation, sumfrequency mixing, difference-frequency mixing, optical parametric oscillation (OPO) and stimulated Raman scattering) including tunability, beam quality, beam walk-off and the effective figure-of-merit are analysed. Materials selection rules for non-linear crystals (for wide transparency, high damage threshold, stability, low absorption and large figure-of-merit) are presented. Techniques using non-critical phase-matching, quasi-phase-matching, waveguided doubling and self-frequency doubling are explored. Features and applications of the new non-linear crystals ofβ-barium borate, lithium triborate (LBO), potassium titanyl phosphate (KTP), KNbO₃ and MgO:LiNbO₃ are presented and compared with other crystals. In addition to a critical review, this paper also presents some new results for the analysis of frequency-conversion efficiency, experimental data of OPO in KTP, LBO for frequency conversion using temperature-tuned non-critical phase-matching and green lasers from the diode-pumped self-frequency-doubling crystal of neodymium yttrium aluminium borate.

     

Non-linear crystals for tunable coherent sources

High-efficiency non-linear crystals suitable for the generation of coherent sources ranging from the deep ultraviolet to mid-infrared (0.16 to 5 µm) are explored. The key parameters for frequency conversion techniques (second-harmonic-generation, sumfrequency mixing, difference-frequency mixing, optical parametric oscillation (OPO) and stimulated Raman scattering) including tunability, beam quality, beam walk-off and the effective figure-of-merit are analysed. Materials selection rules for non-linear crystals (for wide transparency, high damage threshold, stability, low absorption and large figure-of-merit) are presented. Techniques using non-critical phase-matching, quasi-phase-matching, waveguided doubling and self-frequency doubling are explored. Features and applications of the new non-linear crystals of-barium borate, lithium triborate (LBO), potassium titanyl phosphate (KTP), KNbO₃ and MgO:LiNbO₃ are presented and compared with other crystals. In addition to a critical review, this paper also presents some new results for the analysis of frequency-conversion efficiency, experimental data of OPO in KTP, LBO for frequency conversion using temperature-tuned non-critical phase-matching and green lasers from the diode-pumped self-frequency-doubling crystal of neodymium yttrium aluminium borate.     

Reduction of the spectral width and beam divergence of a BBO-OPO by using collinear type-II phase matching and back reflection of the pump beam

We report on the reduction of the divergence and the spectral width of the output of a 355 nm pumped pulsed optical parametric oscillator (OPO) of β-barium borate (BBO). Detailed theoretical investigations indicated that type-IIphase matching in combination with double-passing the pump beam should simultaneously reduce the spectral width and the divergence of the OPO output beam. These predictions are confirmed in the experiments reported in this paper. In fact the bandwidth is reduced by more than a factor of 20 to less than 0.1 nm. Simultaneously the divergence of the OPO waves is reduced in the phase matching plane by more than a factor of 5 to 1.0 mrad. The small divergence and the reduced bandwidth allows efficient frequency doubling of the 5-ns-long visible OPO signal pulses into the UV. Doubling in a 7-mm-long BBO crystal provided conversion efficiencies of up to 35%. Received: 21 August 2000 / Revised version: 11 December 2000 / Published online: 21 March 2001     

Laser diode end-pumped Yb:YAG/LBO green laser

With a type-I critical phase-matching LBO crystal, an intracavity frequency doubled solid-stated Yb:YAG green laser is reported. Using a plano-concave resonator, with pump power of 1.37 W, 24.5 mW TEM₀₀ continuous wave laser at 525 nm was obtained. The optical conversion efficiency is 1.8%. By adjusting the placed angle of LBO, several lasers wavelength from 525.0 to 537.8 nm could be extracted. The maximum output power at 537.8 nm is 3.1 mW.     

Compact 600 mW blue laser with a composite Nd:YAG

A compact and simple design for an LDA-end-pumped intracavity doubling high-power blue laser with a composite Nd:YAG laser on the ⁴F_3/2 to ⁴I_9/2 laser transition in a flat-curved cavity is demonstrated. The nonlinear crystal used in the experiment is an LBO crystal cut for phase-matching type I. Through the thermo-lensing effect of the laser crystal at high-pumped power, the optimum mode-matched and efficient intracavity doubling are realized at the same time. The maximum output power at 473 nm was 600 mW when the absorbed, pumped power of 15 W, and the optical-to-optical conversion efficiency is 4%. The stability of blue output power is 3.2% within 2 h.     

Harmonic and sum-frequency generation of pulsed laser radiation in BBO,LBO, and KD*P

The optical properties of the nonlinear crystals lithium borate (LBO), barium borate (BBO) and deuterated potassium phosphate (KD*P) are compared for second and third harmonic generation of Nd:YAG laser radiation. In an experimental investigation the conversion efficiency has been measured as a function of the energy density of 8 ns long laser pulses, generated by a commercial Nd:YAG oscillator-amplifier system. In LBO and BBO the second harmonic generation saturates at an energy density of about 1.5 J cm^–2 at efficiencies of 55–60%. In KD*P comparable efficiencies (40–55%) require energy densities of 2–2.6 J cm^–2. Similar results are obtained for frequency tripling. In LBO and BBO saturated efficiencies of 20–25% are measured at an energy density of about 1.5 J cm^–2. In KD*P efficiencies of 20% are obtained at energy densities exceeding 2 J cm^–2. Besides for doubling and tripling of Nd:YAG laser radiation the phase-matching is calculated for frequency conversion of tunable laser light. The results demonstrate that in LBO and BBO phase-matched sum-frequency mixing of UV and infrared laser light generates tunable radiation at wavelengths as short as the transmission cut-off at 160 nm and 190 nm, respectively.     

Diode-pumped 671 nm laser frequency doubled by CPM LBO

A design of diode-pumped high-efficiency Nd:YVO₄/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM₀₀ mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively.     

High-power picosecond LiB3O5 optical parametric oscillators tunable in the blue spectral range

The paper reports on an experimental investigation and numerical analysis of noncritically and critically phasematched LiB₃O₅ (LBO) optical parametric oscillators (OPOs) synchronously pumped by the third harmonic of a cw diode-pumped mode-locked Nd:YVO₄ oscillator–amplifier system. The laser system generates 9.0 W of 355-nm mode-locked radiation with a pulse duration of 7.5 ps and a repetition rate of 84 MHz. The LBO OPO, synchronously pumped by the 355-nm pulses, generates a signal wave tunable in the blue spectral range 457–479 nm. With a power of up to 5.0 W at 462 nm and 1.7 W at 1535 nm the conversion efficiency is 74%. The OPO is characterized experimentally by measuring the output power (and its dependence on the pump power, the transmission of the output coupler and the resonator length) and the pulse properties (such as pulse duration and spectral width). Also the beam quality of the resonant and nonresonant waves is investigated. The measured results are compared with the predictions of a numerical analysis for Gaussian laser and OPO beams. In addition to the blue-signal output visible-red 629-nm radiation is generated by sum-frequency mixing of the 1.535-μm infrared idler wave with the residual 1.064-μm laser radiation. A power of 1.25 W of 1.535-μm idler radiation and 5.7 W of 1.064-μm laser light generated a red 629-nm output power of 2.25 W. Received: 2 February 2000 / Revised version: 28 July 2000 / Published online: 22 November 2000     

Non-collinear nanosecond optical parametric oscillator based on periodically poled LN with tilted domain walls

We report on a non-collinear, 1064 nm pumped, 10 kHz repetition rate ns-OPO which consists of a 13 mm long periodically poled lithium niobate (PPLN) crystal in a hemispherical optical cavity. The non-collinear phase-matching is achieved by tilting the domains by 60° with respect to the pump beam. This phase-matching avoids back conversion of signal and idler radiation into pump radiation and thus improves the spatial quality of the generated OPO radiation considerably. At a pump power of 5.5 W the OPO provided a conversion efficiency of up to 34%. The generated OPO pulses with a total power of up to 1.85 W were emitted in an almost diffraction limited beam with a M²-value of 1.1. The beam quality did not change when the pump power was varied in the range of 2–5 W. PACS 42.65.-k; 42.65.Yj     

Efficient generation of a CW 593.5-nm laser by intracavity sum-frequency mixing with a BiB<Subscript>3</Subscript>O<Subscript>6</Subscript> (BIBO) crystal

A compact, efficient yellow-orange light at 593.5 nm was realized by the intracavity sum-frequency mixing using a BIBO crystal in a diode-pumped Nd:YVO₄ laser. At an incident pump power of 3.5 W, up to 126 mW of CW output light at 593.5 nm was achieved with a 1.5-mm-long critical phase-matching BIBO. The optical-to-optical conversion efficiency was up to 3.6%, which was comparable to a 5-mm-long LBO. The beam equality was excellent with an ellipticity of 0.97 and output noise of less than 0.8% (rms). Results confirm that the BIBO is an efficient material for frequency conversion in the visible region.     

Nonlinear optical properties of (B3O7)5- and (B3O6)3- groups

3 O₅ (LBO) crystal has been studied by using the bond valence theory of complex crystals. Chemical bond parameters and linear and nonlinear optical (NLO) properties of each type of constituent chemical bonds are quantitatively determined. Because of the different crystal structure characteristics of LBO from those of β-BaB₂O₄ (BBO), the two anionic groups, (B₃O₇)^5- in LBO and (B₃O₆)^3- in BBO, play different roles in contributions to their own total NLO tensor coefficients of LBO and BBO, respectively. By comparison, we find that planar (B₃O₆)^3- groups are the ideal structure model, leading to little cancellation of contributions of each kind of bond in these groups, and this gives us a useful guide to design new NLO materials in the future. Received: 24 January 1997/Accepted: 27 March 1997     

KGW 晶体外腔式高功率579 nm喇曼黄光激光器

报道了579 nm高功率KGd(WO₄)₂喇曼晶体外腔式喇曼黄光激光器的输出特性.基于808 nm脉冲激光二极管侧面泵浦Nd:YAG陶瓷、腔内BBO电光晶体同步延迟调Q和Ⅰ类临界相位匹配的LBO晶体腔外倍频方案,并通过外腔式KGW晶体Ng轴二阶斯托克斯喇曼频移,获得了579.54 nm黄光激光输出.当脉冲信号重复频率为1 kHz、532 nm泵浦光最高平均功率为5.02 W、脉冲宽度为10.1 ns时,获得了最高平均功率2.58 W、脉冲宽度7.4 ns、峰值功率348.6 kW的579.54 nm二阶斯托克斯喇曼黄光激光输出;532 nm至579.54 nm的光-光转化效率为51.4%、斜率效率为54.8%,光束质量因子M_x-579.54²=5.829、M_y-579.54²=6.336,输出功率不稳定性小于±2.35%.实验表明:外腔式喇曼结构能够高效地获得喇曼黄光,具有很高的光-光转化效率及良好的功率稳定性,并通过脉冲LD结合同步延迟电光调Q可获得高重复频率、高平均功率、窄脉冲宽度和高峰值功率的黄光激光输出.     

Intracavity sum-frequency generation of CW blue light in Nd:LuVO<Subscript>4</Subscript> laser

We report for the first time a continuous-wave (CW) blue laser emission by sum-frequency mixing in Nd:LuVO₄ crystal. Using type-I critical phase-matching (CPM) LBO crystal, a blue laser at 493 nm is obtained by 1066 and 916 nm intracavity sum-frequency mixing. The maximum laser output power of 520 mW is obtained when an incident pump laser of 18.2 W is used. At the output power level of 520 mW, the output stability is better than 2.8%. The beam quality M ² value is are about 1.22 and 1.31 in both horizontal and vertical dimensions respectively.     

Travelling-wave 1.57-µm optical parametric oscillator driven by a pulsed multimode Nd3+:YAG laser

The generation properties of an optical parametric oscillator (OPO) with a three-mirror ring resonator have been investigated under conditions of a pulsed pump by multimode radiation from a Nd³⁺:YAG laser. KTP crystals were used as the OPO nonlinear medium. At pump energies up to 100 mJ, decreasing the diameter d of the Nd³⁺:YAG laser beam causes a decrease in OPO radiation divergence and an increase in the generation efficiency at λ = 1.571 μm despite a decrease in the differential efficiency. At d = 2.25 mm and a KTP crystal total length of 40 mm, the efficiency of the pump conversion to the signal-wave pulse reaches 36.5%. Based on the traveling-wave OPO, a compact, highly effective, eye-safe laser source radiating pulses of up to 35 mJ in energy, 11 nsec in duration, and 10 Hz in repetition rate at electrical pump energy of ≤ 8 J is developed. At the 86.5% level of the total pulse energy, the source-beam divergence does not exceed seven diffraction limits. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 516–523, July–August, 2008.     

Spectral properties and numerical modelling of a critically phase-matched nanosecond LiB3O5 Optical Parametric Oscillator

We report on the spectral properties and numerical modelling of a singly resonant Optical Parametric Oscillator (OPO) of Lithium-triBOrate (LBO). The OPO is pumped by the second, third or fourth harmonic of an injection-seeded,Q-switched Nd:YAG laser. The measured OPO parameters are the tuning range, the threshold, the spectral linewidth, the efficiency and the output power. For the LBO-OPO critical type-I phase-matching (xy-plane) provides a wide tuning range and optimum values of the effective nonlinear coefficient. Pumped, for example, by the 355nm third harmonic the spectral range extends from 414 nm to 2.47 µm. With a 15 mm long crystal the OPO generates a total output-pulse energy of 77 mJ with an efficiency of 45%. For 266 nm pump radiation the signal wave is in the near ultraviolet at 307–325 nm. If pumped at 532 nm the OPO generates simultaneously two pairs of signal and idler waves in the infrared (0.707–2.15 µm). The pulse-energy fluctuations of the two pairs are correlated. If, however, the OPO is injection-seeded at one of the signal waves the two wavelength pairs are anti-correlated. The observed wavelength tuning as well as the measured spectral line-widths, threshold energies and efficiencies are in agreement with the values predicted by computer simulation.     

一种新型晶体GdCa4O(BO3)3的非线性光学性能研究

计算和测量了ＧＣＯＢ晶体的相位匹配曲线,理论计算与实验测量结果符合的很好。用电光调Ｑ的Ｎｄ：ＹＡＧ激光器对５ｍｍ和匠ＧＣＯＢ晶体进行了倍频研究,得到了２６．７％的倍频转换效率。并与同样长度的ＢＢＯ晶体进行比较,得出了ＧＣＯＢ晶体的有效非线性光学系数接近ＢＢＯ晶体的有效非线性光学系数的结论。     

Harmonic generation in bismuth triborate (BiB3O6)

We report a study of second- and third-harmonic generation in BiB₃O₆ (BiBO). The effective nonlinearity, phase-matching angle, acceptance bandwidth, and walk-off are calculated and analyzed within the principal planes of the optical indicatrix. In the experiment, the phase-matched harmonic generation is investigated within the xz and yz planes. Also, the temperature dependence of the noncritical phase matching for laser radiation propagating along the z axis is measured for second-harmonic generation (SHG) at crystal temperatures of 25–265^∘C. The corresponding wavelengths of the laser radiation are in the range of 1.16 to 1.34μm. In addition, SHG of 1342-nm radiation of a q-switched Nd:YVO₄ laser system is investigated for noncritical and critical phase matching. The achieved conversion efficiencies are 59% and 20%, respectively. Besides SHG, third-harmonic generation (THG) of 1064-nm, ns laser pulses is investigated. The measured conversion efficiency is as high as 34%. For THG the properties of BiBO are compared with those of BBO and LBO.     

Self‐phase‐locked degenerate femtosecond optical parametric oscillator based on BiB3O6

A self‐phase‐locked degenerate femtosecond optical parametric oscillator (OPO) based on the birefringent nonlinear material, bismuth triborate, BiB₃O₆, synchronously‐pumped by a Kerr‐lens‐mode‐locked Ti:sapphire laser at 800 nm is described. By exploiting versatile phase‐matching properties of BiB₃O₆, including large spectral and angular acceptance for parametric generation and low group velocity dispersion in the optical xz plane, stable self‐phase‐locked degenerate OPO operation centered at 1600 nm is demonstrated using collinear type I (e → oo) interaction in a 1.5‐mm crystal at room temperature. The degenerate OPO output spectrum extends over 46 nm (∼5.4 THz) with 190 fs pulse duration for input pump pulses of 155 fs with a bandwidth of 7 nm. Phase coherence between the pump and degenerate output is verified using f‐2f interferometry, and discrete frequency beats caused by different carrier‐envelope‐offset frequencies are measured using radio frequency measurements. Photo shows a 1.5‐mm BiB₃O₆ crystal used as a nonlinear gain medium in a degenerate self‐phase‐locked femtosecond OPO operating at room temperature. The green beam is the result of non‐phase‐matched sum‐frequency mixing between the pump light and the sub‐harmonic OPO field at degeneracy.