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。

TWO DIMENSIONAL MEASUREMENT OF PICOSECOND LIGHT PULSES BY VOLUME HOLOGRAPHIC METHOD IN PHOTOREFRACTIVE CRYSTAL

In this paper,a novel method for the measurement of spatially two-dimensional temporal amplitude function of two coherent short light pulses with picosecond order is described.It is refered this method as the volume holographic method (VHM). In recording process,the sampling and the object pulses intersect in a thick recording medium and form a holographic grating.Since the interference fringe,and consequently the grating,is formed only when both pulses meet,the sampling pulse cuts a short portion out of the object pulse successively as it propagates in the medium,mapping the time evolution of the object pulse into space.The amplitude of this portion of the object pulse determines the modulation of the interference fringe.If the pulse duration is much shorter than the time of carrier recombination,diffusion and drift of the photorefractive medium,then amplitude of short light pulses form a photorefractive grating is proportional to the amplitude correlation function of the two pulses.The grating formation,the mapping of time into space,the measurable range,resoulution and influence of beam coupling are discussed. In readout process,the envelope of a grating in a volume holographic medium is calculated from diffraction of a CW beam.The diffraction by a volume hologram is expressed by the coupled wave equations. The feasibility of this method was experimentally proved by means of a photorefractive LiNbO₃:Fe crystal and a 3.5ps frequency doubled mode locked Nd:YAG laser.The diffraction of a CW He-Ne laser by the grating formed in crystal.