Abstract
We present a method for the measurement of small optical absorption coefficients. The method exploits the deformation of cavity Airy peaks that occur if the cavity contains an absorbing material with a nonzero thermorefractive coefficient or a nonzero expansion coefficient . Light absorption leads to a local temperature change and to an intensity-dependent phase shift, i.e., to a photothermal self-phase modulation. The absorption coefficient is derived from a comparison of time-resolved measurements with a numerical time-domain simulation applying a Markov-chain Monte Carlo algorithm. We apply our method to the absorption coefficient of lithium niobate doped with magnesium oxide and derive a value of . Our method should also apply to materials with much lower absorption coefficients. Based on our modeling, we estimate that, with cavity finesse values of the order of , absorption coefficients of as low as can be measured.
© 2010 Optical Society of America
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