Encoding and decoding of amplitude or phase informations with a liquid-crystal array on femtosecond light pulses

1.通过傅里叶变换合成，使用由IBM-PC控制的市售液晶空间光调制器（SLM）产生了非线性形状的飞秒激光脉冲。该调制器由128个100 μ m宽的可单独编程像素组成，每个元件之间的间隙为3 μ m。脉冲整形装置由一个光栅对构成，光栅对置于焦距为15 cm的单位放大率共焦透镜对的焦平面上。(1)采用模拟退火优化算法，针对任意形状的振幅和相位时程，设计了实验中由SLM形成的纯相位掩模。甚至时域中的不对称形状也可以用0、（]SY ±-）四个灰度级来合成。[)pi/2和pi。(2)实验中成功地实现了对-100 fs输入脉冲的整形，如7长M序列整形的THz脉冲串、非对称脉冲串和线性调频脉冲.利用脉冲整形装置合成的THz脉冲序列在Bi中激发出选择性相干声子模.利用该脉冲整形装置，我们成功地对光谱宽度为-17nm的超辐射发光二极管连续光进行了相干整形。作为飞秒光谱全息术的初步实验，采用空间相位编码方法记录了多路复用全息图。由用准噪声相位图案和单个波瓣形成图案编码的光束记录的全息图仅在读取光束用相同的准噪声相位图案编码时才成功地产生单个波瓣光束图案。

1. Arbitrarily shaped femtosecond laser pulses are produced with a Fourier-transform synthesis using a commercially available liquid-crystal spatial light modulator (SLM) controlled by a IBM-PC.The modulator consists of 128 individually programmable pixels of 100 mum wide with a 3 mum gap between each elements. The pulse-shaping apparatus consists of a grating pair placed at the focal planes of a unit magnification confocal lens-pair with a focal length of 15cm.(1) Phase-only masks formed with the SLM in the experiments were designed with simulated annealing optimization algorithm for arbitrarily shaped amplitude and phase time histories. Even asymmetric shapes in time domain can be synthesized with four gray levels of 0, (]SY.+-。[)pi/2, and pi.(2) Successful shaping of -100 fs input laser pulse was obtained in our experiments such as THz pulse trains shaped with 7-length M-sequence, unsymmetrical pulse trains, and linearly frequency-chirped pulses.2. Selective coherent phonon mode was excited in Bi with THz pulse trains synthesized with our pulse shaping apparatus.3. Utilizing this pulse shaping apparatus, we succeeded to shape coherent function of a cw light from a super luminescent diode with a spectrum width of -17nm.4. Multiplexed holograms were recorded with spatial phase encoding method as a preliminary experiments of femtosecond spectrum holography. Holograms recorded by a beam encoded with a quasi-noise phase pattern and a single lobe formation pattern, successfully produce a single lobe beam pattern only when a read beam is encoded with the same quasi-noise phase pattern.