Hannover 2010 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 54: Laser Applications: Optical Measurement Technology I

Q 54.4: Talk

Thursday, March 11, 2010, 14:45–15:00, F 342

Measuring small absorptions using the thermal Kerr effect — •Nico Lastzka, Jessica Dück, Sebastian Steinlechner, and Roman Schnabel — Institut für Gravitationsphysik, Leibniz Universität Hannover und Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) Callinstrasse 38 D-30167 Hannover

The precise measurement of small absorption in optical materials is a challenging task. To measure absorption coefficients of some ppm/cm or smaller it is necessary to use indirect methods, which do not measure the power losses but the effect of the absorbed power in the substrate. These are for example calorimetric measurements or methods using the thermal lens effect. The sensitivities of these methods scale with the substrate length and with the input power, and typically high input power is necessary.

We present an absorption measurement scheme based on the shape of the airy peaks of a scanned optical resonator. Due to the heating of the intra-cavity material, the transmitted as well as the reflected airy peaks show a hysteresis depending on the scan direction. A time domain simulation based on the theory of Hello and Vinet is used to fit the measured data. In order to prove the quantitative results of this method the absorption coefficient of a lithium niobate was measured and compared to literature values. An estimation of the lower limit of the measurable absorption coefficient and corresponding error bars is given.