Self-pumped phase conjugation in rhodium-doped BaTiO(3) with 1.06-microm nanosecond pulses

Efficient internal-loop self-pumped phase conjugation is demonstrated in a photorefractive rhodium-doped barium titanate crystal by repetitively pulsed nanosecond pulses from a Q-switched Nd:YAG laser operating at 1.06 microm . Phase-conjugate reflectivities as high as 32% are obtained with a response time of ~5 min at a repetition rate of 30 Hz. The ability of the phase conjugator to correct severe phase distortions is also demonstrated.     

Multi-functional real-time optical processor with self-pumped phase conjugator of Cu:KNSBN

A multi-functional real-time optical processor with a self-pumped phase conjugator of Cu:KNSBN crystal is presented. The key device, self-pumped phase conjugator, has functions of both a mirror and a real-time recording medium in the processor.     

Self-Pumped Phase Conjugation in a Ce:BaTiO3 Crystal Pumped with Femtosecond Laser Pulses at 1053 nm Wavelength

Self-pumped phase conjugation in a cerium-doped barium titanate crystal pumped with femtosecond laser pulses at a 1053 nm wavelength was experimentally studied. A reflectivity of a self-pumped phase conjugation as high as 15#x0025; was demonstrated.     

Directional scattering and self-pumped phase conjugation in photorefractive crystal

The directional scattering in photorefractive SBN crystal is reported.The self-pumped phase conjugation has been realized with the feedback of this directional scattering andthe performance parameters are compared with those of cat self-pumped phase conjugator.     

双光折变晶体半线性相位共轭器的自脉动

在由两块光折变BaTiO3晶体(其中一块晶体为全内反射式自抽运相位共轭镜工作方式,起外反射镜作用)构成的半线性自抽运相位共轭器中观察到了相位共轭光的自脉动现象。自脉动的平均频率f与入射光功率I0的关系为f∝I01.43;相位共轭光的平均维持时间ΔT与入射光功率I0近似成反比。观察到光折变BaTiO3晶体中扇形散射光具有动态的空间结构,扇形散射光的这种特性是引起上述半线性自抽运相位共轭器中相位共轭光脉动的原因     

Generation of double pulses in-line by using reflective Dammann gratings

Doubled femtosecond laser pulses in-line are needed in the collinear pump-probe technique, collinear second harmonic generation frequency-resolved optical gating (SHG FROG) and the spectral phase interferometry for direct electric-field reconstruction (SPIDER), etc. Normally, it is generated by using a Michelson's structure. In this paper, we proposed a novel structure with two-layered reflective Dammann gratings and the reflective mirrors to generate doubled femtosecond laser pulses in line without transmission optical elements. Angular dispersion and spectral spatial walk-off are both compensated. In addition, this structure can also compress the positive chirped pulse, which cannot be realized with a Michelson's structure. By adopting triangular grating and blazed gratings, the efficiency of the system would in principle be increased as the Michelson's scheme. Experiments demonstrated that this method should be an alternative approach for generation of the double compressed pulses of femtosecond laser for practical applications.     

Temporal Behavior of Phase Conjugate Wave in Self-Pumped Phase Conjugator with Internal Total Reflection

Several temporal behaviors of the phase-conjugate output of a self-pumped phase conjugator with internal total reflection in BaTiO₃ crystal have been investigated as a function of the beam entrance position and incident angle on the crystal. Different sets of these conditions cause different behavior of phase conjugate wave which are unstable or pulsed output as well as temporally stable output. Classification of these temporal behaviors in phase conjugate wave by incident condition are shown.     

COMPETITION BETWEEN SELF-PUMPED AND MUTUALLY-PUMPED PHASE CONJUGATIONS IN A BaTiO3 BRIDGE PHASE CONJUGATOR

This paper reveals the inter-dependence and the competition between self-pumped and mutually-pumped phase conjugations, and deals with the periodic instabilities in the phase conjugate output of a BaTiO₃ bridge phase conjugator. It presents experimental data demon-strating these instabilities and also gives evidence that the addition of the second heam in a bridge phase conjugator can affect the self-pumping threshold for the first beam. A mathe-matical model is developed to explain the observed output oscillations.     

Wavelength-stable, narrow-spectral-width oscillation of an AlGaInP diode laser coupled to a BaTiO3:Co stimulated photorefractive backscattering phase conjugator

3 ) stimulated photorefractive backscattering (SPBS) phase conjugator. The SPBS process was successfully achieved by the combination of the short-wavelength diode laser and the highly doped photorefractive BaTiO₃:Co crystal. The spectral width of the diode laser is reduced to 7.2 pm because of the narrow spectral bandwidth of the gratings [with wave number of K=2k(2k gratings)] formed in the SPBS phase conjugator, compared with the transmission grating formed in the conventional cat conjugator, which was used previously. The SPBS phase conjugator was successfully used to suppress self-frequency scanning, and wavelength-stable oscillation of the SPBS phase-conjugator-coupled diode laser was achieved. Received: 4 November 1996/Revised version: 12 February 1997     

COMPETITION BETWEEN SELF-PUMPED AND MUTUALLY-PUMPED PHASE CONJUGATIONS IN A BaTiO3 BRIDGE PHASE CONJUGATOR

This paper reveals the inter-dependence and the competition between self-pumped and mutually-pumped phase conjugations, and deals with the periodic instabilities in the phase conjugate output of a BaTiO₃ bridge phase conjugator. It presents experimental data demon-strating these instabilities and also gives evidence that the addition of the second heam in a bridge phase conjugator can affect the self-pumping threshold for the first beam. A mathe-matical model is developed to explain the observed output oscillations.     

Properties of cat mutually pumped phase conjugation and two-wave mixing gain in doped KNSBN

Cat mutually pumped phase conjugation configuration is discovered and investigated by using two-wave mixing in (KyNa1-y)2z(SrxBa1-x)1-zNb2O6 (KNSBN) crystal. When only one signal or pumped beam does not give birth to phase conjugation, the maximum reflectivity of signal and pumped beam attain 140% and 30% due to two-wave mixing, respectively. The experimental results show that the two-wave mixing can reduce the threshold of incident beams power, extend the incident angle range, and shorten response rate in the process of self-pumped phase conjugator (SPPC) in KNSBN crystal.     

实时图像反转与实时图像高低通滤波

报道了以Ｃｅ，Ｆｅ：ＬｉＮｂＯ３薄晶体作记录介质，利用Ｔｉ，Ｃｕ：ＫＮＳＢＮ晶体猫式自泵浦位相共轭镜供反向读出光新型实时光学处理器，该处理器可以实现图像反转，图像高，低通滤滤等操作。文中还给出了基于全息记录与擦除、自衍射与尺寸效应等的机理解释。     

Integrated-grating-induced control of second-harmonic beams in frequency-doubling crystals

We report a novel type of integrated nonlinear photonic device for controlling the generation of several second-harmonic beams. Two-dimensional diffraction gratings are recorded with femtosecond laser pulses at the entrance surface of a frequency-doubling crystal. This periodic spatial modulation of the material surface induces noncollinear propagation of the fundamental input signal in the crystal. By slightly changing the angle of incidence of the seed beam, collinear and noncollinear phase matching can be achieved between different diffraction orders, in this way allowing the efficient generation of several second-harmonic beams.     

高能量掺Yb偏振型大模场面积光子晶体光纤孤子锁模飞秒激光器

实验研究了基于掺Yb偏振型大模场面积光子晶体光纤的孤子锁模激光器,获得了高脉冲能量的飞秒激光输出. 激光器基于线形腔结构,利用光栅对补偿腔内色散,并通过半导体可饱和吸收镜实现锁模的自启动. 实验中从振荡级直接获得了平均功率为700mW, 重复频率为47.3MHz(对应于14.8 nJ的单脉冲能量),脉冲宽度为518 fs的稳定锁模脉冲输出. 与普通孤子锁模飞秒光纤激光器相比,输出的单脉冲能量提高了两个数量级. 关键词： 光子晶体光纤 飞秒 光纤激光器 孤子锁模     

Fast response self-pumped phase conjugator based on a +c-face incident configuration in a pentagon-shaped BaTiO3 crystal

We propose a novel geometry for a self-pumped phase conjugator that uses a +c-face incident configuration in a photorefractive pentagon-shaped 0°-cut BaTiO₃ crystal for obtaining fast response in phase conjugation. A steady phase-conjugate output with a fast response time 0.4 s is obtained when the incident beam has a 4 W/cm² intensity. The influences of position and angle on the temporal phase-conjugate response are also investigated. The advantage of this phase conjugator using this novel configuration is improved resolution of a phase-distorted image with a value as high as 128 lp/mm.     

Theoretical analysis of noncollinear phase-matched optical parametric generation in BBO crystal

In this article we propose a theoretical treatment of noncollinear phase-matched femtosecond parametric interaction process pumped by ultrashort optical pulses, and investigated the pulse characteristics of OPG in BBO crystal. The results show that the major factors, which affect the optical parametric conversion coefficient and durations of the pulses, are the group velocity mismatch and the phase mismatch among the three ultra-short pulses. In addition, the material dispersion can cause the durations of the pulses to increase when pump pulse is below 20 fs, and its influence becomes more obvious at low pump intensity.     

Dispersion measurements for femtosecond-pulse generation and applications

Dispersive phenomena provide limits in the generation, measurement and applications of femtosecond optical pulses. Optical elements such as prisms, gratings, air, mirrors, filters, and laser crystals all contribute to the total dispersion in optical systems. Interferometric techniques enable measurements of dispersion of individual elements, and new techniques allow dispersion measurement inside the cavity of operating modelocked femtosecond tunable lasers. These techniques provide access to detailed information about dispersion errors which can distort pulses and produce undesirable effects in modelocked lasers. In this article, we review techniques for the measurement of dispersion in optical components and systems. In several cases, we compare measurements made with intracavity dispersion techniques with extracavity measurements and point out common features.     

Optical phase conjugation in nonresonant and saturable absorptive/resonant systems

Recent results obtained at Alabama A&M University on optical phase conjugation in electrically unpoled BaTiO₃, BANANA and SBN crystals are presented. The decay curves of the transient gratings and phase conjugation in these crystals indicate the involvement of more than one exponential process, possible reasons for which are indicated. Self induced gratings have been studied in electrically unpoled SBN crystal using a He−Ne Laser. The oscillations in a ring passive phase conjugator (RPPC) and in a unidirectional ring resonator using an electrically poled BaTiO₃ crystal have, been found to be bistable. It is also found that bistable oscillations are possible in a geometry in which the crystal is used simultaneously in a RPPC and as a linear passive phase conjugate (LPCC) mirror. The auxiliary oscillations pumped by the RPPC are bistable with the oscillations in LPCC. A brief review of the recent literature on phase conjugation in saturable absorptive/resonant systems along with the experiments planned to be undertaken by the authors on such systems are presented.     

飞秒激光在光子晶体光纤中产生超连续光谱机制的实验研究

报道了利用零色散在780nm处的光子晶体光纤与纳焦耳量级的飞秒激光脉冲相互作用的实验结果.实验使用35fs，中心波长810—840nm，单脉冲能量可达14nJ的飞秒激光光源获得了超过一个倍频程的平坦超连续光谱（500—1100nm）.在不同功率、不同中心波长、不同啁啾和有无直流成分的多种飞秒脉冲激光的条件下，研究了超连续光谱的产生情况.并对一系列现象进行了对比，分析了超连续光谱产生的机制. 关键词： 光子晶体光纤 飞秒脉冲激光 超连续光谱