Degenerate four-wave mixing experiments in Methyl green dye-doped gelatin film

Degenerate four-wave mixing (DFWM) was performed in Methyl green dye-doped gelatin films using continuous-wave laser radiation () generated by a He-Ne laser of total power 35 mW. Various parameters which influence the phase-conjugate (PC) signal during the DFWM process were studied. The PC signal contributions from induced holographic transmission and reflection gratings were measured. We observed a maximum PC beam reflectivity of 0.13% in these dye-doped gelatin films.     

Optical phase-conjugation in erioglaucine dye-doped thin film

Optical phase-conjugation (OPC) has been demonstrated in erioglaucine (acid blue 9) dye-doped gelatin films via continuous-wave degenerate four-wave mixing (DFWM) using a low-power He-Ne laser at 633 nm. DFWM and holographic processes are found to contribute to the observed phase-conjugate signal. A maximum phase-conjugate beam reflectivity of about 0.24% has been observed in these dye-doped gelatin films.     

Optical Phase Conjugation in Polyesters with Cyanoazobenzene Units in the Side Chain

Efficient optical phase-conjugate (PC) signals in four kinds of novel polyester films containing cyanoazobenzene units in the side chain are reported. One of them can efficiently generate only the photoinduced anisotropy (PA) component of PC signal, while the other three films can simultaneously generate two types of PC signals, PA and holographic components. These polymers have good potential not only as a phase conjugator but also as a polarization-sensitive hologram-recording material.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994     

Phase conjugation in fluorescein film by degenerate four-wave mixing and holographic process

Phase conjugation is performed in a fluorescein film by a cw Ar ion laser of the wavelength 0.488 μm in a degenerate four-wave mixing (DFWM) configuration. It becomes apparent that the phase conjugate wave is generated simultaneously by not only DFWM but also a holographic process and that the DFWM and holographic components of the phase conjugate wave have different time constants.     

Organic dye-doped polymer films for optical phase-conjugate processing

Erythrosin B-doped polyvinyl alcohol (EB/PVA) film, a methyl-orange-doped polyvinyl alcohol (MO/PVA) film and a (EB+MO)/PVA film serve as not only phase conjugators but also hologram-recording media. A phase-conjugate (PC) wave is generated even when a probe wave is linear-polarized orthogonal to the pump polarization direction. Using these dye-doped films, we demonstrate optical PC processing for detecting the phase and amplitude difference between two objects and a moving or time-varying object in a backward degenerate four-wave mixing arrangement.     

Nonlinear refraction and photoinduced birefringence in chlorophosphonazo I doped polymer thin films

The nonlinear refraction and photoinduced birefringence of chlorophosphonazo I (CPA I ) doped PVA thin films were investigated. The single-beam Z-scan measurement showed that CPA I doped PVA thin film possessed a large value of nonlinear refractive index (n₂=1.82×10⁻¹² cm²/W) under a pulse 532 nm excitation, and the mechanism accounting for the process of nonlinear refraction was discussed in term of resonant electronic effect. Moreover, fast and stable molecular reorientation was observed when investigating the photoinduced birefringence of CPA I doped PVA thin film with a CW 532 nm laser as pump light and a CW 650 nm laser as probe light.     

染料掺杂液晶填充毛细管的激光发射特性研究

本文提出利用染料掺杂液晶填充PI光控取向膜毛细管获得可调谐激光.采用532 nm YAG倍频脉冲激光器抽运,实验及理论研究了有聚酰亚胺(PI)取向膜和无PI取向膜毛细管的激光发射特性,对比分析了两种情形的激光产生阈值以及随温度变化的特性.结果表明:经PI光控取向处理的染料掺杂胆甾相液晶毛细管的激光发射模式具有分布反馈模式和回音壁模式,同时,激光产生阈值为4.5 m J·mm~(-2);发现当温度升高时,发射光谱发生"蓝移",中心波长调谐范围为5.9 nm,温度升高到43℃时,形成质量非常好的回音壁模式,其自由光谱范围为1.05 nm.经PI光控取向处理的染料掺杂向列相液晶激光发射模式为随机激光,并且较无PI取向时激光发射峰减少.     

Frequency Regime of Generation of a Holographic Distributed Feedback Dye Laser

We carried out an experimental investigation of the frequency regime of generation of a holographic distributed feedback (DF) dye laser. We show that the convection induced in liquid by heating-up a solution in the excitation zone ensures self-pumping of the solution through this zone that is sufficient for stable operation of the laser in the regime of frequently repeating pulses without forced circulation of the solution through the cuvette. It is found that the main condition for the operation of a DF-laser in this regime is the sharp focusing of pumping radiation, which ensures transverse dimensions of the generation zone of less than 1 mm. In experiments, we produced stable generation of a holographic DF dye laser in the regime of self-pumping of a solution with a pulse repetition rate of up to 1 kHz with an efficiency of 10% and a spectral line width of 0.01 nm.     

杂环偶氮染料薄膜的全息光存储

采用含杂原子的偶氮染料TADEB、DMTAM、DMTAA和DMTAMB掺杂高分子聚合物PMMA制成薄膜,利用四波混频全息光路系统,研究了它们的全息光存储性质。实验结果显示DMTAA样品的衍射效率最高,可达到22%,是一种存储性能较为优良的永久性全息光存储介质材料。     

用体全息术对皮秒光脉冲进行二维测量

本文提供一种测量两束相干的ps光脉冲的空间二维时间振幅相关函数的新方法.在此方法中,光脉冲是被记录在一种光致折变的体积全息介质中,而所记录的信息可以通过直接量度在介质中所形成的光栅的空间分布而读出.这种方法可的可行性已为实验证实,它是通过3.5ps倍频锁模Nd:YAG激光测量光致折变晶体LiNbO₃来实现的。     

Fast optical recording in dye-doped liquid crystals

Light-induced director reorientation in dye-doped nematic liquid crystals was recently reported to be an efficient method of writing permanent holographic gratings with high sensitivity [Phys. Rev. Lett. 82, 1855 (1999)]. We report the achievement of stable director reorientation in the same materials by means of a single 4-ns pulse of the second harmonic of a Nd:YAG laser. Fast recording of high-resolution holographic gratings (more than 500 lines/mm) can be obtained with an energy density as low as 7x10(-3)J /cm(2) .     

用于激光聚变驱动器的全光纤、全固化光脉冲产生系统

报道一种全固化、全光纤的用于高功率激光驱动的惯性约束聚变驱动器的光脉冲产生系统,采用单纵模振荡器输出连续激光信号,经过相位调制器和振幅调制器,得到一个时间波形上已整形且具有一定带宽(约0.1 nm)的激光脉冲,经光纤放大器放大并经光纤分束器分束后同时输出四路激光脉冲,各路激光脉冲先通过时间同步调整单元精确控制时间同步关系后,经可编程光纤衰减器调节各路之间的功率平衡后再通过光纤放大器做进一步放大并通过150 m光纤传输输出至预放系统.该光纤系统可输出0.3—20 ns、带宽0.1 nm、能量数纳焦的几乎任意 关键词： 激光聚变驱动器 前端 光纤激光系统     

Degenerate four-wave mixing based on excited-state absorption in azo-dye-doped polymer films

Degenerate Four-Wave Mixing (DFWM) based on excited-state absorption in azo-dye doped polymer films is firstly reported. Under a pre-exciting argon laser at 514.5 nm, DFWM is performed using a 632.8 nm HeNe laser which is absorbed only slightly when the molecules are in the ground state. The dynamic behavior of the DFWM signal due to excited-state absorption is also treated theoretically.     

基于PVA／AA光致聚合物的衍射光锥产生机理及其抑制

研究了以He—Ne激光器作为记录光源,以He-Ne、Nd：YAG和He-Cd激光器作为读出光源的亚甲基蓝敏化的PVA／AA体系光致聚合物的全息衍射光锥现象。衍射光锥现象的产生是由于入射光透过全息记录材料内部的不均匀结构或缺陷所产生的噪音光栅所致。运用Ewald球对此现象产生的机理进行了解释,利用全息光散射理论结合三角学...     

Photoinduced High-Density Phase of Exciton-Polariton Masses and their Coherent Propagation at Stacking Fault Interface in BiI 3

Photoinduced high-density phase of exciton-polariton masses excited at a two-dimensional stacking fault interface in BiI 3 has been studied by observing the degenerate four-wave-mixing (DFWM) signals. It was found that the increase in the dephasing rate due to exciton-exciton collisions is suppressed above a threshold excitation density. Above such density, a coherently propagating component of the exciton masses was detected on the space-resolved DFWM signals obtained by applying the spatially isolated two-spot excitation with a picosecond laser. In this scheme the off-diagonal element of the density matrix of the excitons at the one exciting laser spot propagates to the other, bringing about nonlinear polarization to yield the DFWM light. Time evolution of the space-resolved DFWM signals reveals evidently the macroscopic expansion of the exciton-polariton masses in a photoinduced condensed phase. Energy splitting of the DFWM spectra obtained with a narrow-band laser shows a repulsive interaction between the excitons.     

基于低散射和高增益全息液晶/聚合物光栅的分布反馈式激光器

利用低官能度的丙烯酸酯单体进行全息液晶/聚合物光栅的制备, 获得了具有聚合物支撑形貌的光栅结构. 由于这种光栅内部不存在液晶微滴, 当作为分布反馈式激光器的谐振腔时, 可以有效降低光栅内部的散射损失(<4%), 降低激光腔损耗. 此外, 选用的高折射率单体提升了光栅的折射率调制量, 增强了光栅的反馈增益. 在以上两种因素的共同作用下, 采用染料DCM为激光工作物质, 以532 nm的Nd:YAG脉冲激光器作为抽运光源, 最终获得了中心波长为635 nm, 转化效率为1.2%的高性能激光, 在以阈值能量0.8 μJ/pulse抽运下获得激光线宽0.3 nm, 较之国内外同类激光器的报道, 在阈值、线宽、转化效率三方面均有不同程度提升.     

Change in optical path length of saturable absorbing dye-doped polymer films under laser irradiation

The cause of the change in the optical path lengthΔ(nd) of the saturable absorbing dye-doped polymer films under laser irradiation is investigated using polyvinyl alcohol and gelatin films doped with erythrosin B. The temperature rise of the dye-doped films, the changes in optical path length, film thickness, the refractive index and the optical density of the dye-doped films are measured under laser irradiation. The thermal expansion due to the temperature rise of the dye-doped films caused by the irradiation has greater effect on theΔ(nd) than the fading of dye molecules due to the irradiation of laser beams.     

Two-Step degenerate four-wave mixing as a means to decrease pre- and post-filtering effects in optically thick media

The use of crossed beam 2-Step Degenerate Four-Wave Mixing (2S-DFWM) for decreasing pre- and post-filtering effects under optically thick conditions has been investigated. 2S-DFWM is a technique in which the DFWM process is performed between two excited states of which the lower one is populated by an ordinary laser excitation from a low lying, highly populated state. Experiments were performed on Au in an acetylene/air flame. We have shown that under conditions where ordinary (one-step) DFWM experiments are significantly affected by pre- and post-filtering effects (i.e., partly absorption of the pump, probe or signal beams prior to or after the interaction region) the 2S-DFWM technique can give virtually interference free signals. A variety of different laser beam and flame configurations have been investigated. It was found that the use of a crossed beam geometry, where the first step exciting laser is incident upon the interaction region perpendicular to the DFWM beams, completely eliminated severe pre- and post-filtering effects occurring for an ordinary single-step DFWM scheme in an optically thick medium.     

High-power Yb-doped continuous-wave and pulsed fibre lasers

High-power laser generation using Yb-doped double-clad fibres with conversion efficiencies in excess of 80% have attracted much attention during the last decade due to their inherent advantages in terms of very high efficiency, no misalignment due to in-built intracore fibre Bragg gratings, low thermal problems due to large surface to volume ratio, diffraction-limited beam quality, compactness, reliability and fibre-optic beam delivery. Yb-doped fibres can also provide a wide emission band from ～1010 nm to ～1170 nm, which makes it a versatile laser medium to realize continuous-wave (CW), Q-switched short pulse, and mode-locked ultrashort pulse generation for various applications. In this article, a review of Yb-doped CW and pulsed fibre lasers along with our study on self-pulsing dynamics in CW fibre lasers to find its role in high-power fibre laser development and the physical mechanisms involved in its generation has been described. A study on the generation of high-power CW fibre laser of 165 W output power and generation of high peak power nanosecond pulses from acousto-optic Q-switched fibre laser has also been presented.     

基于透射式液晶/聚合物光栅的分布反馈式激光器的研究

本文研究了染料掺杂透射式液晶/聚合物光栅的制备以及基于透射式液晶/聚合物光栅的分布反馈式激光器的激光特性.实验选取DCM作为激光染料,制备了周期为586 nm的掺杂DCM的透射式液晶/聚合物光栅;使用532 nm输出的Nd ∶YAG倍频脉冲激光器作为抽运光源对染料掺杂液晶/聚合物光栅进行侧面抽运,得到了中心波长为603 nm的窄线宽、低阈值激光输出.激光线宽为1.4 nm、阈值能量约为17.3 μJ,与之前国外的报道相比,阈值能量有了很大幅度的降低. 关键词： 液晶/聚合物光栅 分布反馈式激光器 阈值 线宽