Photothermal multipixel imaging microscope

Abstract

ABSTRACT Photothermal microscopy is a useful nondestructive tool for the identification of fluence-limiting defects in optical coatings. Traditional photothermal microscopes are single-pixel detection devices. Samples are scanned under the microscope to generate a defect map. For high-resolution images, scan times can be quite long (1 mm 2 per hour). Single-pixel detection has been used traditionally because of the ease in separating the laser-induced topographical change due to defect absorption from the defect surface topography. This is accomplished by using standard chopper and lock-in amplifier techniques to remove the DC signal. Multi-pixel photothermal microscopy is now possible by utilizing an optical lock-in technique. This eliminates the lock-in amplifier and enables the use of a CCD camera with an optical lock in for each pixel. With this technique, the data acquisition speed can be increased by orders of magnitude depending on laser power, beam size, and pixel density. Keywords: Photothermal microscopy, absorption, nondestructive testing, multilayer coating 1 INTRODUCTION Fluence-limiting defects in optical coatings can be differentiated from benign defects with photothermal microscopy.