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Experimental Study On A Pulse Compressor Based On Stimulated Brillouin Scattering

Posted on:2012-08-27Degree:MasterType:Thesis
Country:ChinaCandidate:Y ZhangFull Text:PDF
GTID:2120330335951192Subject:Optics
Abstract/Summary:PDF Full Text Request
The effect of stimulated Brillouin scattering is popularly used at the areas of underwater detection laser pulse modification fiber sensor and so on. The effect of stimulated Brillouin scattering becomes to be a pop subject to research, because of the pursuit of high quality laser. Beside the feature of pulse compression, it also has many other features, for example, a small amount of frequency shift, phase conjugation, scattered light back transmission and high conversion efficiency and so on. So pulse compression based on stimulated Brillouin scattering can ensure the quality of beam is the same as the pump laser, after compensating the phase distortion. The phenomenon of phase conjugation and pulse compression phenomenon is associated with each other, so pulse compressing by stimulated Brillouin scattering can modify the quality of the laser, to obtain the high power short pulse laser. For the reasons above, it is a effective manner to obtain the short pulse laser by stimulated Brillouin scattering.Stimulated Brillouin scattering is a stimulated scattering which is a nonlinear optical effect occurs in the medium. Because of the high density and good coherence, the effect of random fluctuation will happens when the laser inject into the media and the scatter light will interfere with the pump light coupling with the medium. So the density of the scatting light is greatly enhanced, which is relevant to the pump light. It has the phase conjugation between the scatter light and the pump light. As a result, the pulse is compressed.In order to obtain the short pulse laser without optical breakdown to insure the safe performance of the pulse compressing instrument, we need to choose the appropriate design and parameters for the fittings. We should also study the relationship of phase transition pulse width and energy reflectance with the energy of pump light, in order to obtain good shape, reflection high energy, short pulse laser. For these reasons, this article is divide into two parts to research the relationship between parameters of the instruments with the pulse compression:the design of the instrument selection and determine the fittings' parameters, experimental research and analysis.In the part of the design of the instrument selection and determine the fittings' parameters, we give some introduction of several laser pulse compression devices, and analyze the structure of various pulse compression device and the advantages and disadvantages, such as:the single-cell pulse compression device, multi-cell pulse compression device which can obtain picosecond pulse. According to the laboratory conditions and requirements, we decided to use two-cell pulse compression device as our design, and make some appropriate improvements based on original device. Through theoretical analysis and calculation, we analyze the efforts of lens, media, the length of pools of the device impact on the pulse compression. The final design of the water as the medium, amplified pool length 150 cm, length of generation pool 30cm, lens focal length of 12.5 cm, without beam expander lens group, two-cell pulse compression device. During the process of set up, we detail the steps to build the device, and summed up the relatively simple methods to build up this device.In the experimental study part, we do a series of experiments by Nd:YAG laser whose wavelength is 532 nm,, the results of pulse compression is compared between the lens focal length of 12.5 cm and 25.0 cm device respectively. As observed in the experiment, the phenomenon of phase transitions emergences in the tails of the compressed pulse with the energy of pump laser increases. Because the energy of the pump light grows, the Stokes of high energy density excitation the second-order Stokes generating in the medium with the energy of pump increases. When the energy of second-order Stokes reached the threshold of stimulated Brillouin scattering, it will produce backscattering third-order Stokes, as a result, phase transition will Occur at the tail of the pulse compressed. As observed in the experiment, the phase transitions threshold of the pulse compression devices of long focal length is higher than that of short focal length.The efforts of pump energy and the lens focal length impact on the pulse compression and energy reflectivity are also analyzed. The stimulated Brillouin scattering threshold of device with short focal length is much lower, as a result, higher energy Stokes seed light can be obtained; high-energy pump light can promote the growth of the Stokes seed light. Pulse compression device with short focal length under high-energy pump light is more efficiency in pulse compression. As to the reflectance of energy, when the energy of pump light is higher than the threshold of stimulated Brillouin scattering, the energy of compressed pulse will increase with the pump energy increasing. The pulse compression device with short focal length can get higher energy reflectivity, for stokes seed light generated in it can grow rapidly.This article is the experimental results on pulse compression device based on stimulated Brillouin scattering, it can provide academic reference of optimized the device design and building.
Keywords/Search Tags:stimulated Brillouin scattering, Pulse Compression, Phase Conjunction, Phase Transition
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