Technology Research Of Thin Film Damage Identification By Plasma Spectrometry

With the development of laser technology to high energy and high power, optical thin film as an important part of laser system, determination and improve the laser damage resistance of optical thin films is very important. Damage threshold is the key parameter of optical thin film laser damage resistance, under the intense laser inter action, accurately judge the film damage is a prerequisite to study the damage threshold of optical thin films.The popular film damage detection methods are studied and analyzed in depth, summarizes the advantages and advantages of each detection method. Based on the traditional plasma flash method, a new method of film or optical element damage detection is proposed-plasma spectrometry discriminate damage. Acquisition and analysis technology of flash spectrum are studied, spectral acquisition system is established on optical thin film under the action of laser, and the system consists of laser, laser damage threshold test instrument, optical fiber spectrometer and a computer.When the laser irradiated film surface cause flash, using fiber spectrometer receives flash spectrum, extracting spectral peak position, because of the essential differences between membrane element with atmospheric elements, and these elements spectral peak position is determined, will not be changed with changes in test conditions, spectral peak is uniquely determined by the film material elements. Compare the characteristic peak of flash spectrum distribution between atmospheric and film samples, take the differences between the emission peak positions as the basis of judgment film damage.The preparation of a set of procedures for the use of MATLAB software, including smoothing filter which based on the least square method, wavelet transform-based filtering, peak searching which based on the two order differential algorithm, comparison between test data and atmospheric flash spectral database, get the conclusion of whether film was damaged. To validate the algorithm, when the film sample laser damage occurred, flash spectrum curve is collected by the experimental device. Using the algorithm presented in this paper for flash spectra processed, to verify the recognition algorithm, observation of film damage by 100 times microscope. The results showed:Plasma Spectrometry discriminating film damage is not only feasible, but also discriminate accuracy, wide range of thin film materials.