Stable operation of a cw optical parametric oscillator near the signal-idler degeneracy

The frequency stability of a cw optical parametric oscillator (cw OPO) near the signal-idler degeneracy has been studied. The strong tendency of a near-degenerate OPO to mode hop has been suppressed by using a bulk Bragg grating as a spectral filter in the OPO cavity. An experimental demonstration of stable parametric oscillation in a single longitudinal mode of the OPO cavity is reported, together with the capability of tuning the signal-idler difference frequency from 1 to 4 THz. The OPO has potential use in cw terahertz generation.     

Harmonic repetition-rate femtosecond optical parametric oscillator

We report on a femtosecond optical parametric oscillator (OPO) with a repetition rate of 1 GHz, which is 12 times that of the pump laser used. We also introduce a novel method for operating an OPO with a high harmonic repetition rate which is not determined by the cavity length of the OPO, but rather the cavity length difference between the OPO and its pump laser. Operation of an OPO at 4-times the harmonic repetition rate has been carried out to show the feasibility of this method. The new approach paves the way for constructing a femtosecond OPO working at repetition rates of 10 GHz, or higher, when the pump laser used has a relatively low repetition rate. Received: 26 October 2001 / Revised version: 11 Januar 2002 / Published online: 14 March 2002     

Comparative studies of eye-safe intracavity and extracavity optical parametric oscillators with an unstable telescopic cavity

We have experimentally studied the lasing characteristics of an eye-safe optical parametric oscillator (OPO) with an unstable telescopic cavity when it is placed inside (intracavity OPO) and outside (extracavity OPO) the plane-parallel cavity of a pulsed, nearly single-mode KGW:Nd pump laser. We used a KTP crystal as the nonlinear medium for the OPO. We have shown that the intracavity OPO has the higher lasing efficiency. We have observed that the distribution of nonlinear losses introduced by the intracavity OPO, nonuniform over the cavity cross section, leads to an increase in the diameter and divergence of the radiation beam from the pump laser and a dependence of its temporal lasing dynamics on the transverse beam coordinate. We propose a physical model qualitatively explaining the spatial and temporal lasing dynamics of a radiation source with an intracavity OPO. Both OPO versions generate beams of radiation with about the same divergence. When the KGW:Nd laser has an electrical pumping energy of 7.3 J and a cavity length of 77 cm, the intracavity OPO and the extracavity OPO emit pulses with energies of 14.5 mJ and 12.0 mJ and duration 18 nsec and 13 nsec respectively. The divergence of the eye-safe radiation (λ = 1.578 μm) at 86.5% of the total pulse energy is no greater than 5.5 mrad for an OPO output beam diameter of = 2 mm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 535–543, July–August, 2006.     

低频压缩态光场的制备

低频压缩态光场可用于提高引力波探测器灵敏度, 近年来受到人们的广泛关注. 相对于高频段而言, 低频压缩态的产生更容易受到外界环境噪声的干扰而不易被观察到. 本文采用全固化单频倍频Nd: YVO4/KTP激光器作为光源, 利用双波长共振的光学参量振荡器实现参量过程, 以1064 nm波长的红外作为基频光, 激光器腔内倍频产生的532 nm绿光作为抽运光, 通过调节周期性极化磷酸氧钛钾晶体温度使光学参量振荡器达到双波长同时共振, 采用真空注入的方式, 利用Pound-Drever-Hall锁腔技术锁定抽运场. 输出压缩光通过平衡零拍探测, 最终在实验上获得了频率低至3 kHz的真空压缩, 所直接观察到的压缩度为2 dB.     

ZnGeP2 parametric oscillator pumped by a linewidth-narrowed parametric 2 microm source

A tandem optical parametric oscillator (OPO) is used to convert radiation from 1.064 microm to the mid-infrared. Spectral bandwidth narrowing close to 80 times compared with a conventional cavity was achieved by using a bulk Bragg grating as an outcoupler in a near-degenerate periodically poled KTiOPO(4) OPO. The narrowed 2,008 nm radiation was subsequently used for pumping the ZnGeP(2) OPO, which was tunable between 3.3 and 5.2 microm. Pulse energies of 170 microJ and pump depletion close to 70% were obtained in the ZnGeP(2) OPO. To our knowledge this is the first time the output from a near-degenerate type I PPKTP OPO has been used for ZnGeP(2) OPO pumping.     

行波光参量过程的理论与实验研究

通过对行波光参量三波耦合过程时域特性的理论计算,预示了光参量时域过程可能存在“弛豫”振荡,理论与实验相结合分析了抽运光强度、晶体长度、腔长、输出耦合系数等一系列参数对参量输出的影响,并采用一种新的棱镜环形腔进行实验,得到从０．４１～２．６ｕｍ的连续宽调谐输出和２２％折能量转换效率。     

对应于铯原子D1线连续可调谐正交压缩态光场的制备

铯原子D₁线的非经典光由于其波长接近于量子点的独特优势,在固态量子信息网络的发展中有着重要的应用前景.在之前的工作中,利用两镜连续简并光学参量振荡器中的参量下转换过程,制备出2.8 d B正交压缩真空态光场.然而,所产生光场的压缩度较低,对于对压缩光具有实用意义的可调谐性能也未做进一步探究.理论分析表明,光学参量振荡器后腔镜对信号光透射率的增加及内腔损耗的减小可以提高压缩度.因此,本文在该研究基础上,通过使用高光洁度腔镜及优化腔镜镀膜参数等方式对光学参量振荡器进行改良,降低了光学参量腔阈值,获得压缩度为3.3 d B的单模正交压缩真空光.当光学参量腔运转为参量反放大状态时,在系统稳定运行的情况下,制备的明亮压缩态光场能够连续调谐80 MHz,为其在量子信息网络中的应用奠定了良好的基础.     

高功率腔内双共振2μm光参量振荡器特性研究

报道了一种稳定的高功率双共振2?μm 光参量振荡器（OPO）. 该OPO使用调Q的线偏振全固态Nd∶YAG激光器作为抽运源,利用双棒串接补偿热致双折射和双Q开关正交放置技术提高了抽运源的输出功率和光束质量,通过腔内抽运单块KTP晶体实现了稳定的高功率2?μm 激光输出. 在调Q频率为5?kHz时,得到了295 W的2?μm 激光输出. 研究了OPO输出功率同KTP晶体温度和声光Q调制频率的关系,并测量了在29W时2?μm激光的功率稳定性. 在1 h内该OPO的功率起伏小于1.4%. 关键词： 光参量振荡器 2?μm激光器 KTP晶体 双共振     

飞秒光学参量振荡器中谐振腔的最佳聚焦设计

本文运用ABCD定律对光学参量振荡器共线谐振腔的聚焦参数及其匹配进行了计算分析。数值计算给出了当OPO腔增益最高时,泵浦光聚焦透镜焦距及聚焦束腰尺寸随振荡光聚焦镜曲率半径的变化及相应的拟合曲线,并对结果进行了讨论。在考虑非线性晶体的接收角的情况下,讨论了光束聚焦镜容许的最短曲率半径。计算同时指出,非临界相位匹配结构比临界相位匹配结构具有更大的接收角.     

Fine tuning of a triply resonant OPO for generating frequency degenerate CV entangled beams at low pump powers

A method of achieving triple resonance in a frequency-degenerate but polarization-non-degenerate optical parametric oscillator (OPO) with external mirrors is illustrated. The OPO is brought to the triple-resonance condition by tuning the non-linear crystal temperature and tilting the cavity axis. The interplay among temperature and tilting mismatch and gain is analyzed together with the allowed ranges of variation of these parameters. The method has been successfully applied to an OPO based on a periodically poled KTP crystal. Calibration of the system is reported together with parametric gain and squeezing measurements below threshold as a test of reliability and efficiency. PACS 42.50.-p; 42.65.-k     

LD侧泵的声光调Q Nd∶YAG/KTP人眼安全激光器

为获得人眼安全的激光,在一个由激光二极管（LD）阵列侧泵、声光调Q的Nd∶YAG激光器谐振腔中放置一非临界相位匹配的KTP晶体,形成了一个内腔式光学参量振荡器,实现了准连续的1.57 μm激光振荡.通过对单谐振光学参量振荡器阈值公式进行讨论,采用了平凹腔的结构和尽可能短的光学参量振荡器腔长,有效地降低了光学参量振荡器的泵浦阈值.测量了不同声光重复率和不同透射率输出镜下光学参量振荡器输出的各项特性参量.分析了声光重复率和输出镜的透过率对光学参量振荡器的泵浦阈值和输出脉冲波形的影响,并对实验中出现的饱和现象作了解释.当泵浦电流14.5A,声光重复率10 kHz,光学参量振荡器输出镜透过率15%时,在保持单脉冲输出的情况下,获得了1.57 μm激光的最高平均功率输出值1.748 W.     

Comparison between shared and coupled resonators for passively Q-switched Nd:GdVO4 intracavity optical parametric oscillators

Comparison between the shared and coupled resonators for the intracavity optical parametric oscillators pumped by passively Q-switched Nd:GdVO₄ lasers is experimentally made. The shared and coupled resonators are found to be complementary in the performances of the pulse repetition rate, pulse duration and pulse energy. It is also found that the output signal pulses of the shared cavity explicitly display the mode-locking phenomenon. On the whole, the amplitude stability of the shared cavity configuration is substantially superior to that of the coupled cavity configuration. PACS 42.60.Gd; 42.65.Yj; 42.55.Xi     

First-Stokes Wavelengths at 1175.8 and 1177.1 nm Generated in a Diode End-Pumped Nd:YVO_4/LuVO_4 Raman Laser

A diode end-pumped acousto-optic Q-switched Nd:YVO_4/LuVO_4 Raman laser is demonstrated. Both YVO_4 and LuVO_4 can work as Raman gain, and slightly different active vibration modes of both crystals can result in different first-Stokes wavelengths. The output characteristic as the Raman competition between YVO_4 and LuVO_4 crystals for the laser systems with both shared cavity and coupled cavity is experimentally investigated.For the shared cavity, simultaneous Raman conversion in both YVO_4 and LuVO_4 crystals is achieved with dualwavelength emission at 1175.8 and 1177.1 nm. The maximum output power of 1.03 W and the conversion efficiency of 10.3% are obtained. The 0.84 W single first Stokes wavelength at 1177.1 nm with LuVO_4 Raman conversion is achieved with the coupled cavity. The results show that the coupled cavity with short Raman cavity can obtain a narrow pulse width. The separated laser crystal and Raman gain media with different vanadates in shared cavity have advantages in achieving dual-wavelength lasers with small frequency intervals.     

非简并光学参量振荡腔的经典增益

采用双晶体串接,温度调谐及光楔补偿方法,实现了参量振荡腔内泵浦场与非简并亚谐波场之间的三模同时共振,测定了系统的经典增益,实验结果与半径典理论计算符合.     

Narrowband tuning of an injection-seeded pulsed optical parametric oscillator based on a self-adaptive, phase-conjugate cavity mirror

Narrowband tuning of a pulsed optical parametric oscillator (OPO) is achieved with a self-adaptive injection-seeded optical cavity employing a phase-conjugate reflector. This approach is used in a novel OPO system based on periodically poled KTiOPO4 and pumped at 532 nm by a pulsed Nd:YAG laser. The OPO is injection seeded at 835-855 nm by a continuous-wave tunable diode laser, which also enables a Rh:BaTiO3 photorefractive crystal to act as a wavelength-selective phase-conjugate reflector, with no need for active control of cavity length. The single-longitudinal-mode tunability and operational simplicity of this OPO system are demonstrated experimentally.     

Wide single-mode tuning of a 3.0- 3.8-mum, 700-mW, continuous-wave Nd:YAG-pumped optical parametric oscillator based on periodically poled lithium niobate

A new optical parametric oscillator (OPO) for the mid-infrared wavelength region of 3-3.8mum with an idler output power of up to 1.5 W has been developed. The singly resonant OPO is pumped by a single-mode, 10-W, continuous-wave Nd:YAG laser and consists of a bow-tie ring cavity with a fan-out periodically poled lithium niobate crystal and a low-finesse intracavity air-spaced etalon. The single-frequency idler output can be continuously tuned over 24 GHz with 700-mW power by tuning of the pump laser. The tuning was demonstrated by recording of an absorption line of ethane with photoacoustic spectroscopy.     

Self-guided operation of singly resonant continuous-wave optical parametric oscillator based on bulk MgO-doped PPLN

We report on a self-guided operation of a green-pumped singly resonant continuous-wave optical parametric oscillator with a bulk MgO-doped PPLN crystal. It is achieved by increasing the OPO cavity length beyond the stability boundary so that the OPO can only oscillate with formation of a thermally induced waveguide inside the crystal. The effects of the thermal waveguide on the OPO performance are studied by measuring output power characteristics at different cavity lengths. Improvement of spatial mode quality and stability of output power by self-guiding is demonstrated. Measurement of temporal characteristics proves that formation of the waveguide originates from the photo-thermal effect in the nonlinear crystal by absorption of pump power.     

Development of injection-seeded, pulsed optical parametric generator/oscillator systems for high-resolution spectroscopy

We report the development and application of pulsed optical parametric generator (OPG) and optical parametric oscillator (OPO) systems that are injection seeded with near-infrared distributed feedback diode lasers. The OPG is injection seeded at the idler wavelength without the use of a resonant cavity. Two counter-rotating, beta-barium-borate (β-BBO) crystals are used in the OPG. These crystals are pumped by the third harmonic, 355-nm output of an injection-seeded Nd:YAG laser. An OPO version of the system has also been developed by placing two flat mirrors around the two β-BBO crystals to form a feedback cavity at the signal wavelength. The OPO cavity length is not actively controlled. The output signal beam from the OPG or OPO is amplified using an optical parametric amplifier (OPA) stage with four β-BBO crystals. The frequency bandwidths of the signal and idler laser radiation from OPG/OPA and OPO/OPA systems have been determined to be slightly greater than 200 MHz. The temporal pulses from each system are smooth and near-Gaussian. High-resolution optical absorption measurements of acetylene (C₂H₂) were performed as another check of the frequency spectrum of the idler beam. The frequency-doubled signal output of the OPO/OPA system was used to perform high-resolution, single-photon, laser-induced fluorescence (LIF) spectroscopic studies of the (0,0) vibrational band of the A ²Σ⁺−X ²Π electronic transition of nitric oxide (NO) at low pressure. Excellent agreement was obtained between the theory and the experiment. The signal output of the OPG/OPA system was also used for sub-Doppler, two-photon LIF spectroscopic studies of the same vibration–rotation manifold of NO.This revised version was published online in August 2005 with a corrected cover date.     

Spatial chirp and angular dispersion of the nonlinear crystal for a femtosecond OPO

In this paper spatial chirp and angular dispersion are calculated theoretically and analyzed for a four-mirror, standing-wave cavity femtosecond OPO. The analytical expression of spatial chirp in the nonlinear crystal is deduced. The analytical expressions of second- and third-order dispersion including angular dispersion of the nonlinear crystal are presented, for the noncollinear type-I phase-matched Fs BBO OPO using angle tuning. Moreover, variations of GDD and TOD with cavity parameters are calculated exactly. The analysis method and the obtained result also are efficacious for a same type Fs OPO.     

Widely tunable optical parametric oscillator with electrical wavelength control

A LiNbO(3) optical parametric oscillator (OPO) pumped at 930nm shows a wide phase-matching curve. Each pulse produced by the OPO has a very broad natural linewidth, from 1480 to 1800 nm for the signal and from 1950 to 2550 nm for the idler. The emission wavelength is controlled thanks to an electrically tunable Fabry-Perot interferometer inserted into the OPO cavity. The signal wavelength is electrically tuned in the range 1450-1850nm without crystal rotation.