Application of the laser induced deflection (LID) technique for low absorption measurements in bulk materials and coatings

Abstract

Precise absorption measurements of bulk materials and coatings upon pulsed ArF laser irradiation are presented using a compact experimental setup based on the laser induced deflection technique (LID). For absorption measurements of bulk materials the influence of pure bulk and pure surface absorption on the temperature and refractive index profile and thus for the probe beam deflection is analyzed in detail. The separation of bulk and surface absorption via the commonly used variation of the sample thickness is carried out for fused silica and calcium fluoride. The experimental results show that for the given surface polishing quality the bulk absorption coefficient of fused silica can be obtained by investigating only one sample. To avoid the drawback of different bulk and surface properties amongst a thickness series, we propose a strategy based on the LID technique to generally obtain surface and bulk absorption separately by investigating only one sample. Apart from measuring bulk absorption coefficients the LID technique is applied to determine the absorption of highly reflecting (HR) coatings on CaF 2 substrates. Beside the measuring strategy the experimental results of a AlF 3 /LaF 3 based HR coating are presented. In order to investigate a larger variety of coatings, including high transmitting coatings, a general measuring strategy based on the LID technique is proposed.