基于准相位匹配晶体的宽带可调谐光参量放大过程研究

系统分析了基于准相位匹配晶体的光参量放大过程中极化周期和非共线结构对信号光调谐带宽的影响.提出了最大极化周期的概念,用于描述非共线相位匹配和群速度匹配同时满足时晶体的极化周期所能达到的最大值,给出了用于计算不同温度下周期极化铌酸锂晶体的最大极化周期的数学公式,并确定了宽带可调谐光参量放大过程应使用的最佳非共线结构.当采用此非共线结构时,通过将晶体的极化周期设定为最大极化周期可以在相对最大的波长范围内实现信号光的调谐放大输出.在此基础上提出了一个用于最大化光参量放大过程的信号光调谐带宽、确定工作温度等最佳工作参数以及简化实验操作方法的可行性方案.最后对最大极化周期和非共线结构对光参量放大的参量带宽的影响进行了研究. 关键词： 光参量放大 极化周期 非共线结构 带宽     

宽带准连续光纤激光在周期极化铌酸锂中倍频特性的研究

双包层光纤激光器和非线性光学材料(如周期性极化的铌酸锂晶体,PPLN)相结合,开辟了实用性非线性光学器件的一个新领域。研究了准相位匹配周期性极化反转铌酸锂晶体对宽带准连续光纤激光倍频的温度特性和频谱特性。在理论上,从准相位匹配相位失配关系出发,推导了晶体温度与抽运源中心波长的关系以及温度响应带宽,并和已报道实验结果进行了比较,二者符合得很好。此外,还推导了倍频周期极化铌酸锂晶体对抽运基频光源的响应谱线带宽。在实验上,采用长度20mm,极化周期6．5μm,厚度0．5mm的周期极化铌酸锂晶体光纤激光器准连续宽带输出进行了倍频,获得了在不同控制温度下的倍频光光谱,并对此进行了详细分析。     

周期性极化铌酸锂晶体光参量振荡调谐与容差特性分析

研究了周期性极化铌酸锂晶体光参量振荡的工作机理,并讨论了其波长调谐特性与极化反转光栅周期、抽运光波长与晶体温度的关系.在此基础上,通过对相位失配因子求微分的方案,分析了光参量振荡的增益与光栅周期、抽运光波长与晶体温度的关系,以及光栅周期、抽运光波长与晶体温度容差的关系 关键词： 准相位匹配 周期性极化铌酸锂 光参量振荡     

可调谐准相位匹配高效宽带二次谐波转换

高效宽带二次谐波转换在光通信、信号处理和光谱学等很多领域都有重要的应用.通常高效宽带二次谐波转换的研究都集中在几个波长,为了得到可调谐准相位匹配高效宽带二次谐波转换,理论分析了准相位匹配和群速度匹配条件.在此基础上,分别计算了0型和Ⅰ型准相位匹配情况下,温度对5 mol%掺杂氧化镁周期性极化铌酸锂和周期性极化铌酸锂晶体准相位匹配高效宽带二次谐波转换的影响.对于5 mol%掺杂氧化镁周期性极化铌酸锂晶体,在0型和Ⅰ型准相位匹配情况下,分别得到了调谐宽度15 nm和341 nm的可调谐准相位匹配高效宽带二次谐波转换;对于周期性极化铌酸锂晶体,在0型和Ⅰ型准相位匹配情况下,分别得到了调谐宽度44 nm和98 nm的可调谐准相位匹配高效宽带二次谐波转换.拓展了准相位匹配高效宽带二次谐波转换的波长范围.     

应用于宽带中红外激光产生的啁啾周期极化铌酸锂晶体结构设计及数值模拟

中红外波段3—5μm激光光源在医疗、基础科学、通信、工业等众多领域都有着重要的应用需求,而受制于中红外波段的增益介质,传统的激光产生及放大的方法如再生放大、多程放大、行波放大等已经不适用.为了产生宽带且高能量的中红外激光,本文结合准相位匹配技术和啁啾周期极化铌酸锂(CPPLN)晶体进行了理论分析.通过计算分析铌酸锂晶体的色散关系曲线,对CPPLN晶体的结构参数进行设计和调节.结合非线性耦合波方程组与四阶龙格库塔法对该晶体在800 nm激光的抽运下,与0.95—1.6μm范围内的信号光进行准相位匹配差频转换进行了数值模拟.研究表明,在单块CPPLN晶体中,结合准相位匹配技术,能够高效产生覆盖1.6—5μm的中红外激光.对CPPLN晶体产生中红外激光的理论分析和数值模拟,能够为进一步的实验探究等提供方案参考和理论支持.     

光纤型宽带可调连续波差频产生中红外激光器

报道一种新型光纤化宽带可调连续波中红外激光器系统,该激光系统采用准相位匹配(QPM)的差频产生(DFG)技术,非线性晶体为多周期的周期性极化掺镁铌酸锂晶体(PPMgLN),掺镱光纤激光器(YDFL)用作抽运光源,可调激光器经掺铒光纤放大器(EDFA)功率提升后作为信号光源。利用建立的准相位匹配-差频产生系统,获得了连续波中红外差频光输出;实验发现,温度导致相位失谐的半峰全宽(FWHM)为4.5℃;通过优化选择晶体周期,并结合调节信号光波长和控制温度,该准相位匹配-差频产生系统可在3.1~3.6μm内连续调谐。     

BBO-I非共线光学参变啁啾脉冲放大增益带宽的实验研究

以纳秒级调Q倍频的Nd:YAG激光器为抽运源,以自锁模钛宝石激光器输出并经光栅展宽的800nm啁啾脉冲为信号光,实验研究了其宽带BBO－I非共线相位匹配光学啁啾脉冲放大（OPCPA）的增益谱,研究结果表明,非共线夹角的变化对BBO－I非共线相位匹配光学参变啁啾脉冲放大的增益谱有很大的影响。     

低阈值单谐振周期极化掺镁铌酸锂光参量振荡器

对基于周期极化掺镬铌酸锂晶体的信号光单谐振光学参量振荡器的输出特性进行了实验研究.讨论了光学参量振荡器谐振腔的腔长、周期极化铌酸锂晶体的通光长度、输出镜的透过率以及抽运光的脉冲宽度对光学参量振荡器谐振阈值的影响.光学参量振荡器的抽运源采用输出波长为1 064 nm的声光调Q Nd:YVO_4激光器,在重复频率为2 kHz、周期极化掺镁铌酸锂晶体的温度为30℃的条件下,光学参量振荡器的振荡阈值仅为48 mW.当抽运功率为94 mW时获得了25 mW的信号光输出,其光-光转换效率为26.6%.     

低阈值单谐振周期极化掺镁铌酸锂光参量振荡器

对基于周期极化掺镁铌酸锂晶体的信号光单谐振光学参量振荡器的输出特性进行了实验研究.讨论了光学参量振荡器谐振腔的腔长、周期极化铌酸锂晶体的通光长度、输出镜的透过率以及抽运光的脉冲宽度对光学参量振荡器谐振阈值的影响.光学参量振荡器的抽运源采用输出波长为1 064 nm的声光调Q Nd∶YVO4激光器,在重复频率为2 kHz、周期极化掺镁铌酸锂晶体的温度为30 ℃的条件下,光学参量振荡器的振荡阈值仅为48 mW.当抽运功率为94 mW时获得了25 mW的信号光输出,其光-光转换效率为26.6%.     

高效率中红外2.7μm可调谐激光器

报道了采用1064nm激光抽运周期极化掺杂氧化镁的铌酸锂(PPMgO…CLN)晶体光参变振荡器(OPO)实现高效率2.7μm可调谐激光输出的实验结果,理论计算了PPMgO…CLN晶体准相位匹配(QPM)温度调谐曲线。在1064nm激光抽运功率为182W,声光Q开关工作频率为10kHz和PPMgO:CLN晶体工作温度为150℃条件下,获得了平均功率为36.7W、波长为2.73μm中红外激光输出,斜率效率为23.7%。通过改变周期为31.3μmPPMgO…CLN晶体的工作温度30℃～200℃,获得了中红外波长3.0～2.6μm激光输出,波长温度调谐实验结果与理论分析结果有大约10℃的差异。     

Periodically poled lithium niobate monolithic nanosecond optical parametric oscillators and generators

We fabricated and characterized periodically poled lithium niobate monolithic optical parametric oscillators (OPO's) and generators. The compact monolithic devices were trivial to align and operate and provided widely tunable, nearly diffraction-limited, stable output pulses. Low thresholds and high conversion efficiencies were obtained when the devices were pumped with 3.5-ns 1.064-mum pulses. In addition, the monolithic OPO devices exhibited broad tuning by crystal rotation through noncollinear phase matching. The bandwidth-broadening effects exhibited in the noncollinear phase-matching geometry were measured and explained.     

High-efficiency parametric oscillation and spectral control in the red spectral region with periodically poled KTiOPO(4)

Narrow-linewidth optical pulses at wavelengths near 630 nm with 2.2-mJ energy were generated with 61% efficiency in a periodically poled KTiOPO(4) parametric oscillator pumped by a frequency-doubled Q -switched Nd:YAG laser. The tuning range was extended to 30 nm by a noncollinear elliptical pumping geometry. We demonstrate that by angular dispersion a noncollinear optical parametric oscillator can be used to control the spectral and spatial characteristics of the output signal beam.     

Noncollinear double quasi phase matching in one-dimensional poled crystals

We demonstrate simultaneous phase matching of two different nonlinear processes, using a noncollinear interaction in periodically poled crystal with single grating. The noncollinear scheme provides phase-matching solutions over continuous regions of the optical spectrum and can be used for multiple-harmonic generation as well as all-optical effects. We have demonstrated experimentally third-harmonic generation of a 3 microm pump wavelength in a noncollinear configuration using a periodically poled LiNbO3 crystal. We observed, in good agreement with theoretical calculation, very broad spectral and thermal acceptance bandwidths, as well as a relatively narrow angular bandwidth.     

Broadband nondegenerate optical parametric amplification in the mid infrared with periodically poled KTiOPO4

We theoretically and experimentally demonstrate that the bandwidth in a nondegenerate optical parametric amplifier can be substantially increased by noncollinear interaction in a quasi-phase-matched single-periodicity structure. Broadband amplification of signals between 1540 and 1720 nm was realized in periodically poled KTiOPO4. The achieved signal bandwidth of 6.9 THz at 1680 nm is large enough to accommodate sub-100 fs optical pulses.     

Distributed-feedback optical parametric oscillation by use of a photorefractive grating in periodically poled lithium niobate

We report a demonstration of distributed-feedback (DFB) optical parametric oscillation (OPO) by writing photorefractive gratings in periodically poled lithium niobate (PPLN). The photorefractive DFB structures were fabricated by illumination of PPLN with UV light through a photomask and by writing of PPLN with UV-light gated interfering laser beams at 532 nm. Evidence of OPO was observed from the spectral narrowing at the 1438.8- and the 619.3-nm signal wavelengths from 1064- and 532-nm-pumped PPLN crystals with the DFB grating periods phase matched to the 4084.5- and 3774-nm idler wavelengths, respectively.     

Double quasi phase matching for both optical parametric oscillator and difference frequency generation

We present simultaneous phase matching of optical parametric oscillator (OPO) and difference frequency generation (DFG), using a noncollinear interaction in periodically poled crystal with single grating. Selecting proper grating period Λ and titled angle ξ between the grating vector G and the optical axis of crystal, the noncollinear scheme provides double phase matching solutions over continuous regions of the midwave infrared spectrum. At certain wavelength regions, for DFG process the group velocities between interaction pulses are matching and the phase matching bandwidth reaches maximum. Selecting the different grating period, the broadband midwave tuning and better gain spectrum can be obtained at different wavelength range. For the certain period grating the conversion efficiency is higher. Hence, using the double phase matching configuration, the broadband tunable midwave infrared wave can be produced in single grating. But the configurations have a relatively narrow angular bandwidth.     

Broadband non-collinear double QPM optical parametric amplification in mid-infrared wave

The properties of optical parametric amplification (OPA) based on non-collinear double quasi-phase matching (NDQPM) with single periodically poled KTP (PPKTP) have been investigated theoretically. The NDQPM includes two different non-linear processes: one is optical parametric generation (OPG) and the other is difference frequency generation (DFG). The investigation of our numerical simulation focuses on the gain bandwidth of dependence upon non-collinear angle, grating period and crystal temperature. At a certain non-collinear angle and grating period with fixed temperature, there exists a broadest gain bandwidths of output mid-infrared pulse at 526 nm pump wavelength and certain signal wavelength in PPKTP. These are an optimal values of non-collinear angles and grating period. By accurately tuning the non-collinear angle or temperature near the optimal non-collinear angle, broadband mid-infrared tuning is obtained and an optimal operation of NDQPM can be realized. In this paper, the solutions of the coupled equations of the cascaded processes were discussed, and the spatial-temporal frequency (STF) band of the output idler pulse is analyzed by taking angular dispersion of amplified pulse beam into account. The idler pulse with a certain angular dispersion can improve the OPA bandwidth significantly. So, optical parametric chirped-pulse amplification can be realized in this configuration. For a broadband NDQPM both the acceptance angles and the acceptance temperature are smaller and the gain bandwidth is sensitive to non-collinear angles and temperature, it is important to control the precision of the non-collinear angles and the temperature in experiment.     

Tunable, high-power, narrow-band picosecond IR radiation by optical parametric amplification in KTP

We report on an optical parametric amplifier (OPA) based on two potassium titanyl phosphate (KTP) crystals in a walk-off compensating geometry. An Nd:YLF regenerative amplifier at a 1-kHz repetition rate serves as the pump source. The seed beam is delivered by a synchronously pumped frequency-stabilized optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN). At pump intensities of about 7 GW/cm² large amplification factors of more than 10⁴ were achieved, resulting in pulse energies of more than 450 μJ and 350 μJ for the signal and idler pulses, respectively, at a 1-kHz repetition rate. In the saturation regime the time–bandwidth product increases from two to three times the Fourier limit, with a pulse duration of 105 ps and a bandwidth of 12.7 GHz at the highest intensities employed. Received: 2 November 2001 / Published online: 14 March 2002     

Broadband infrared generation with noncollinear optical parametric processes on periodically poled LiNbO(3)

Broadband signal and idler generation based on the spectral retracing behavior in noncollinear phase matching of optical parametric generation in periodically poled LiNbO(3) (PPLN) is reported. Using PPLN of 29.5-mum quasi-phase-matching period and a Q-switched Nd:YAG laser as a pump, we obtained a broad signal spectrum from 1.66 to 1.96 mum and corresponding idler wavelengths from 2.328 to 2.963 mum. The experimental results were consistent with theoretical predictions. Circular and elliptical pump beams were also compared.