Application Of KrF Laser Induced Fluorescence To Detect The Laser Induced Damage Of Optics

High power krypton fluoride (KrF) excimer laser is an attractive driver to Inertial Confinement Fusion, which has an inherent short wavelength (248 nm), broad band, repetitional rate and outstanding beam spatial uniformity. The damage threshold of optics limits the output of KrF laser because the laser with shorter wavelength is easier to induce damage on the optical elements. The testing of laser damage threshold not only provides an insurance for the laser system development and operation,but also acts as an unique role in the improvement of laser damage threshold. To meet the requirement of the operation and improvement of "Heaven-I" laser system, it is necessary to set up a laser induced damage testing facility to test all kinds of optical elements in our lab.Lots of approaches have been developped to detect and study the damage of optical elements. To test the laser induced damage threshold, the application of the phenomena induced by laser in the optical material will be a potential way to dectect the damage of optical elements.The wavelength of KrF laser is so short that the laser induced fluorescence is salience.To set up a damage testing facility in the lab, the application of KrF laser induced fluorescence to detect the damage of optics is explored. The fluorescence induced by KrF Laser on coating sample before/after damage is compared.It is noticeable that the efficiency of fluorescence induced by laser varies with the development of damage.Once the sample be damaged, the intensity of fluorescence will increase rapidly until the spark of plasma be observed. At the same time, the comparison of KrF laser pulse and fluorescence pulse showes us that the width of fluorescence will increase as soon as the optics is damaged by laser.A fluorescence image system was built to observe aberration of fluorescence profile because of laser induced damage.On account of the high uniformity of KrF laser irradiation,the fluorescence intensity distribution will be aberrated only if the damage is developped.The testing of laser induced damage on all kinds of UV opitcal elements in our lab was accomplished with laser induced fluorescence. The results were the inspected under an ex situ Normaski microscopy .The fluorescence imaging technique, which can meet the requirement of the ISO 11254 standard, is most suitable to detect the laser induced damage in our lab because of it's in-situ testing capability,.