Laser-Modulated-Scattering from optical surfaces using fiber detection

The improvement of optical components for high power laser applications is still topical. Indeed the different significant progress made these last years, had allowed to improve the damage resistance of optical components by in particular, the identification of micronic precursors centers(1,2). A new challenge today is the identification of precursor centers of damage with size in the range of few nanometers. This kind of defects seems to play an important role in the laser damage process(3,4). In any case the challenge is to find an efficient tool able to detect these defects which are invisible with usual techniques(3) as optical microscope or standard scattering. The technique of Laser Modulated Scattering (LMS) has been performed to reach this challenge. This new tool presented last year in the Boulder symposium(5,6), is based on a very high sensitivity detection of photothermal response of the defect. The LMS has been performed via two different setup arrangements. The first one uses two beams as in the configuration of a standard Photothermal microscope (PTM) (7), and the second one uses only one beam. In this article we first briefly remind the principle of the LMS technique with one and two beams. Then we will show by different results, the advantages of using an optical fiber to collect the scattered light instead of a block beam system used before. One of the main advantages of the setup using a fiber, is that it is easily possible to realize an angular study of scattering which allows a best understanding of the physical origin of the defect-induced scattered signal. The last part of this work consist of a series of simulation of angular scattering LMS curve, in order to quantify the sensitivity an the powerfulness of this technique.