Photothermal measurements on optical thin films

Abstract

An overview of the application of the photothermal technique for optical as well as thermophysical characterizations of thin films is given. The peculiarities of this technique are discussed in some detail, and selected important results are pointed out. Emphasis is placed on the influence of both residual absorption and randomly distributed inhomogeneities in thin films on their laser-damage resistance.

Theoretical Study for Detection of Defects in Weakly Absorbing Samples by Crossed-Beam Photothermal Technique

“…WhereKj , kJk,=Klp,cj, Pi' C, (i=I,2,3,4) are the thermal conductivity, thermal diifusivity, density and heat capacity of the region i. Qi (1= 1,2,3) are the heat deposited by the absorption of the region i and are given by: (2a) (2b) (2c) Here Ct i (i= 1,2,3) denote the optical absorption coefficient of region i, Rj (i = 1,2,3) are the reflective coefficients at the interfaces of region OIl, 112,2/3, respectively. Assuming that there are finite temperature steps at the interfaces between regions 1 and 2, 2 and 3, which are determined by thermal interfacial resistance Rl2 and R 23 , the boundary conditions at the interfaces are (3b) (3c) (3d) Due to the cylindrical symmetry of the problem, the differential thermal conduction equations can be solved by standard Hankel transform technique and the temperature rises within the five regions can be expressed as The temperature rise in a two-layered sample with interfacial absorption can be obtained by assuming the second layer is with very small thickness and finite absorption, or solving similar thermal conduction problems.…”

“…Where n i and dnldT (i=1, 2,3) are the refractive index and temperature coefficients of the refractive index oflayer i, respectively, 00 is the incident angle of probe beam, and Oi (i=I,2,3) is the refractive angle at the layer i, which follow Snell law. The normal or transverse components of the probe beam deflection are the sum of those caused by the temperature gradients within the three layers and can be obtained by substituting the temperature distributions within the three layers into equations (Sa) or (Sb).…”

“…Where rj = ~ x; + y~ , (i=1, 2,3), yo is the offset in y direction, J] is the first-order Bessel function of the first kind.…”

Femtosecond laser-induced thermal lens effect in chromium film

“…It has been successfully applied to many diverse areas, such as materials science [13], optical film coating defect inspection [14,15], thermophysical parameters measurement [16][17][18], subnanoliter measurement [19], spectroscopy [20,21], and microscopy [22]. Two types of TL techniques have been reported: mode-matched [23] and mode-mismatched [24] configurations.…”

Optical contamination screening of materials with a high-finesse Fabry-Perot cavity resonated continuously at 106-µm wavelength in vacuum

“…It cannot, however, distinguish the absorption loss from the total cavity loss as required by LIGO. There are a number of techniques such as photoacoustic sensing 4 and photothermal detection 5,6 capable of measuring surface absorption down to the parts per million level; however, none of these techniques can be readily applied to a resonant optical cavity under vacuum. We have chosen an optical absorption loss measurement that is implemented in a resonant optical cavity by evaluation of the shift in beat frequency of two transverse electromagnetic ͑TEM͒ modes resonated simultaneously in the cavity.…”