Abstract
Absolute measurement of residual absorption in optical coatings is steadily becoming more important in thin film characterization, in particular with respect to high power laser applications. A summary is given on the current ability of the laser induced deflection (LID) technique to serve sensitive photo-thermal absorption measurements combined with reliable absolute calibration based on an electrical heater approach. To account for different measurement requirements, several concepts have been derived to accordingly adapt the original LID concept. Experimental results are presented for prominent UV and deep UV laser wavelengths, covering a variety of factors that critically can influence the absorption properties in optical coatings e.g., deposition process, defects and impurities, intense laser irradiation and surface/interface engineering. The experimental findings demonstrate that by combining high sensitivity with absolute calibration, photo-thermal absorption measurements are able to be a valuable supplement for the characterization of optical thin films and coatings.
Highlights
Raising power in laser material processing, finer and finer structures in semiconductor lithography and state-of-the-art optical components are faced with increasing demands and requirements
A summary is given on the current ability of the laser induced deflection (LID) technique to serve sensitive photo-thermal absorption measurements combined with reliable absolute calibration based on an electrical heater approach
This section contains a variety of experimental results in order to show the benefit of using direct absorption measurements for optical coating characterization
Summary
Raising power in laser material processing, finer and finer structures in semiconductor lithography and state-of-the-art optical components are faced with increasing demands and requirements. Absorption, being one of the key parameters in high-end laser applications, is gaining more and more attention due to the undesired effects resulting from thermal lensing like focus shifting, wave front deformation and depolarization. Extinction coefficients obtained by that procedure contain both scatter and absorption contributions because it is not feasible to separate these parts by measuring transmission and reflection spectra. Individual absorption and scattering data are strongly required due to their different potential interferences on the optical system performance. Direct absorption measuring in optical thin films and bulk materials have gained more and more attention in optics qualification to ensure or improve stabile production processes, to prepare particular optical functionalities and to identify potential show stoppers upon use in high-end laser applications
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