权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Coherent Phonon Generation by Periodic Excitation of Transient Grating with a Picosecond Light Pulse Train

通过皮秒光脉冲序列周期性激励瞬态光栅产生相干声子

基本信息

批准号：
62840008
负责人：
HASHI Tsuneo
金额：
$ 6.14万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-62840008/
关键词：
grating phonon ultrasonic wave application of laser 液晶フオノン

项目摘要

Generation of enhanced coherent phonons (ultrasonic waves) was observed by using periodic excitation of transient gratings with a pulse train from a Q-Switched and mode-locked Nd:YAG laser. The enhancement occurs when the resonance condition nu=nf is satisfied, where nu is the frequency of the ultrasonic wave, f is the repetition frequency (82MHz in our case) of the mode-locked laser pulses and n is an integer. The frequency nu is determined from the grating pitch lamda (= /(2sin(theta/2), : wavelength of the light, theta: crossing angle of the laser beams) and the sound velocity v as nu=v/lamda. Detection of the ultrasonic waves was made by using diffraction of a cw or pulsed probe laser beam.Considerable enhancement was observed in ethanol, methanol, ethylene-glycol and water containing small amount of dye ( Na -fluorescein etc., 10^<-2>mol/l) for n=1 to 4(i.e., nu=82 to 328MHz). Generation of ultrasonic waves up to 1.06GHz (n=13) was observed but the enhancement became smaller at higher frequencies.Similar studies were made for liquid crystals MBBA and DOBMMB. Quite different behaviors of ultrasonic waves and thermal gratings were detected for the ordinary and extraordinary probe lights. This is due to the different temperature dependence of refractive indices of these lights. Changes of sound velocity in DOBMMB at phase transition temperatures were also observed.

用调Q锁模Nd：YAG激光器的脉冲序列周期性激发瞬态光栅，观察到增强相干声子（超声波）的产生。当满足共振条件nu=nf时，发生增强，其中nu是超声波的频率，f是锁模激光脉冲的重复频率（在我们的情况下为82 MHz），并且n是整数。频率nu由光栅节距λ（= f（2sin（θ/2），θ：光的波长，θ：激光束的交叉角）和声速v确定为nu=v/λ。用连续或脉冲探测激光束的衍射进行超声波探测，在乙醇、甲醇、乙二醇和含有少量染料（Na -荧光素等）的水中观察到明显的增强，10 μ <-2>mol/l）（即，nu=82至328 MHz）。在1.06GHz（n=13）范围内观察到了超声波的产生，但随着频率的增加，超声波的增强作用逐渐减弱，对液晶MBBA和DOBMMB也进行了类似的研究。在普通探测光和非寻常探测光下，探测到了非常不同的超声波和热光栅行为。这是由于这些光的折射率的不同温度依赖性。还观察到了相变温度下DOBMMB中声速的变化。