Abstract
Optical metrology techniques used to measure changes in thickness; temperature and refractive index are surveyed. Optical heterodyne detection principle and its applications for precision measurements of changes in thickness and temperature are discussed. Theoretical formulations are developed to estimate crystal growth rate, surface roughness and laser cooling/heating of solids. Applications of Michelson and Mach-Zehnder interferometers to measure temperature changes in laser heating of solids are described. A Mach-Zehnder interferometer is used to measure refractive index and concentration variations of solutions in crystal growth experiments. Additionally, fluorescence lifetime sensing and fluorescence ratio method are described for temperature measurement. For all the above techniques, uncertainty calculations are included.
Highlights
Optical testing/assessment of optical surfaces are usually done using interferometers
Optical heterodyne detection theory has been developed for the measurements of crystal growth, surface roughness of mirrors and laser heating/cooling of solids
Mach-Zehnder interferometers were applied for the measurement of temperature changes in laser heating of Pr3+-doped YAG and Yb3+-doped YAG
Summary
Optical testing/assessment of optical surfaces are usually done using interferometers. In a Fizeau interferometer, the reference and test flats are separated by an air gap Light reflected from these two flats generate interference fringes. Resistive thermometers are susceptible to electromagnetic interference; thermocouples are not suitable in corrosive atmospheres, and liquid thermometers are not suitable for high temperature measurements. The temperature of an optical material may change along the path of the laser beam. Optical techniques are reviewed to measure growth rate and temperature changes. Applications of Michelson, Mach-Zehnder and optical heterodyne interferometers are described in detail, for in situ measurement of material temperature changes, crystal growth rate measurement, and refractive index and concentration changes of solutions. Fluorescence intensity and lifetime based techniques are reviewed for temperature measurements These techniques are useful in harsh environments and in other situations, where conventional methods are not applicable
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