Minimum Absorption Coefficient Available for Measurements Using Time-resolved Photothermal Common-path Interferometry on the Example of Synthetic Crystalline Quartz

Abstract

Using the example of an absorption measurement in synthetic crystalline quartz, which has specific ratios of the physical parameters, it was possible to observe the competition among various effects using a time-resolved photothermal common-path interferometry scheme, namely, the thermo-optical effect, nonlinearity of the refractive index in the heating beam field, and heat diffusion. This competition masks the contribution of the thermo-optical effect weakened by stresses in the heating region, and determines the minimum absorption coefficient that can still be correctly calculated from the measurement results. The time-resolved photo-thermal common-path interferometry scheme facilitates separating the contributions to the measured signal of these effects and increases the measurement range in the direction of smaller absorption values. The amount of absorption in various materials at which such competition occurs depends on the ratio of its physical constants, which is ≤ 10-7 cm-1 for crystalline quartz, ≤ 10-8 cm-1 for quartz glass and ≤ 10-5 cm-1 for crystalline silicon. The problems of using experiment measurements of small absorption values in samples of synthetic crystalline quartz are discussed using an example crystal grown through the hydrothermal method at the Russian company Quartz Technologies.

Keywords

• minimum measurable absorption
• refractive index nonlinearity
• thermo-optical parameter
• heat diffusion
• synthetic quartz crystal