Measuring small absorptions by exploiting photothermal self-phase modulation

N. Lastzka, J. Steinlechner, S. Steinlechner, R. Schnabel*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


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 dn/dT or a nonzero expansion coefficient alpha(th). 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 7 mol. % magnesium oxide and derive a value of alpha(LN) = (5.9 +/- 0.9) x 10(-4)/cm. 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 10(4), absorption coefficients of as low as 10(-8)/cm can be measured. (C) 2010 Optical Society of America
Original languageEnglish
Pages (from-to)5391-5398
Number of pages8
JournalApplied Optics
Issue number28
Publication statusPublished - 1 Oct 2010
Externally publishedYes



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