A diffraction theory of continuous-wave photothermal deflection (PD) spectroscopy with fundamental and harmonic responses is presented. The displacement of the probe beam centroid is found to be a rigorous measurement of PD effect, which leads to a set of analytical solutions to the fundamental and the second-order harmonics. Harmonics are caused by the diffraction of the probe beam in the mirage region, which could not be handled by geometric-optics theory. This theory can be used to study bulk materials, thin films, and layered-structure samples. Experimental results are in good agreement with the theory.
© 2002 Optical Society of America
(050.1960) Diffraction and gratings : Diffraction theory
(070.4340) Fourier optics and signal processing : Nonlinear optical signal processing
(350.5340) Other areas of optics : Photothermal effects
Jianhua Zhao, Jun Shen, and Cheng Hu, "Continuous-wave photothermal deflection spectroscopy with fundamental and harmonic responses," Opt. Lett. 27, 1755-1757 (2002)