Absorptance measurements for the DUV spectral range by laser calorimetry

The determination of absorptance in optical components is of crucial interest in respect to their power-handling capability. As a fundamental loss mechanism in the DUV/VUV spectral range, the absorptance is a significant parameter to decide the applicability of an optic in the industrial facilities. The established measuring technique of laser-calorimetry in accordance to the standard ISO 11551 was adapted to the wavelength of the ArF-laser (λ = 193 nm). The present paper describes the developed set-up considering the problems of calibration in the DUV spectral range. In detail, the electrical and optical calibration method were performed and different effects are discussed with regard to the practicability of both procedures. Furthermore, the reduction of scattered light in combination with a remarkable increase in sensitivity is demonstrated. As typical substrate materials for optical components at this laser wavelength, fused silica and Cap₂ were investigated determining the absorptance. Simultaneously, the characteristic luminescence spectrum has been recorded during the investigations.