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Frequency domain analysis of spreading-constriction thermal impedance Rev. Sci. Instrum. 84, 024901 (2013) Modified data analysis for thermal conductivity measurements of polycrystalline silicon microbridges using a steady state Joule heating technique Rev. Sci. Instrum. 83, 124904 (2012) Apparatus to measure adsorption of condensable solvents on technical surfaces by photothermal deflection Rev. Sci. Instrum. 83, 114905 (2012) Note: Development of a microfabricated sensor to measure thermal conductivity of picoliter scale liquid samples Rev. Sci. Instrum. 83, 106102 (2012) High-resolution thermal expansion measurements under helium-gas pressure Rev. Sci. Instrum. 83, 085111 (2012) Additional information on Rev. Sci. Instrum.

A simple, highly sensitive technique for measuring absorbed power in thin film dielectrics based on thermal lensing is demonstrated. Absorption of an amplitude modulated or pulsed incident pump beam by a thin film acts as a heat source that induces thermal lensing in the substrate. A second continuous wave collimated probe beam defocuses after passing through the sample. Determination of absorption is achieved by quantifying the change of the probe beam profile at the focal plane using a four-quadrant detector and cylindrical lenses to generate a focus error signal. This signal is inherently insensitive to deflection, which removes noise contribution from point beam stability. A linear dependence of the focus error signal on the absorbed power is shown for a dynamic range of over 10. This technique was used to measure absorption loss in dielectric thin films deposited on fused silica substrates. In pulsed configuration, a single shot sensitivity of about 20 ppm is demonstrated, providing a unique technique for the characterization of moving targets as found in thin film growth instrumentation.