Acoustic resonance laser calorimetry for measurements of low optical absorption

Abstract

A novel method of acoustic resonance laser calorimetry (ARLC) for the determination of low optical absorption coefficients of crystals and glasses is introduced. It is based on measurements of the kinetics of the equivalent temperature of the sample irradiated by the pulse laser radiation. The equivalent temperature of the sample is directly obtained by measuring the frequency changes of its temperature-calibrated acoustic resonances excited by the laser radiation with a corresponding pulse repetition rate. In contrast to the conventional resonant photoacoustic spectroscopy, where the resonance is used for the enhancement of the registered signal, in ARLC, the laser-excited acoustic resonance of the sample acts as a high-sensitivity temperature probe for measurements of its heating kinetics. The ARLC approach was verified by measuring the optical absorption coefficient of the potassium dihydrogen phosphate crystal ( α = 4.2 ⋅ 1 0 − 2 c m − 1 ) at 1064 nm wavelength.

Multipass lock-in thermography for the study of optical coating absorption

“…Self-phase modulation (SPM) [28,29] uses the variation of the transmission spectra shape of a Fabry-Perot interferometer caused by a variation of optical path due to the introduction of a pumped sample in the cavity to obtain the absorption. Finally, we can also cite photoacoustic spectroscopy (PAS) [30][31][32] as another measurement technique using a pulsed laser as a pump and the detection of acoustic waves generated by the local thermal variation inside the sample. With thermography, the temperature can also be measured using a thermal camera [33].…”