Study On Acoustic Identification Method Of Laser Damage In Thin Films

As the development of laser to the high power and high-energy direction, laser induced damage of the film has become the focus of attention. Laser damage threshold has become an important performance indicator in the optical thin films. When a new kind of optical components put into use, the determination of damage threshold is essential. There are many methods for testing laser damage threshold at present. But no matter what kind of threshold calculation method, the decision to film damage is very critical and essential.In the present paper, acoustic method is applied to determine thin films damage. Acoustic model of laser-induced thin film has been proposed. The model on the sound waves of thin films damage divides into three stages, which is the thermal expansion stage, the gasification stage and plasma stage. The collection of sound waves and analysis technology are studied, and the laser damage optical thin film of sound waves collection system is established. The laser energy is divided into different levels. Acoustic signals under different levels of laser energy are collected. By analyzing and processing of these acoustic signals, we get the sound characteristics of different laser energy; At the same time, damage of films are magnified 100 times, and the sound and thin-film damage is one-on-one mapped. Eventually, we find the acoustic identification basic of damage in thin films.As the same thin-film sample under different laser energy damage, the characteristics of the acoustic signal is studied; the situation of different thin films is studied also. Through experiments on thin films samples of ZrO2, DLC and so on, when the same thin films damage under different laser energy, the acoustic signals have common characteristics. After the peaks of the second level, wave peak showed a decreasing of exponential relationship, and the decreasing function expressions has been obtained. Also found that when the film damage, amplitude of the acoustic signal is higher than 80mV. For the laser-induced damage of different thin films, acoustic signals have common characteristics. These characteristics are the basis of the acoustic method to distinguish film damage. According with the acoustic method of distinguish the film damage, we experiment DLC films. The results are consistent with image discrimination method. Experiments show that this study of the acoustic method to distinguish the thin films damage is not only feasible, but also reveals the law of thin films damage and acoustic characteristics, and to provide a basis for the acoustic study of thin films damage.