ULTRA-LOW-LEVEL ABSORPTION MEASUREMENT OF ION ASSISTED ELECTRON BEAM DEPOSITED OPTICAL THIN FILMS BY PHOTOTHERMAL COMMON-PATH INTERFEROMETRY

Date

2023-12-28

Author

Kasap, Yusuf

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This thesis delves into Ion Assisted Electron Beam Deposition as an alternative deposition technique for the fabrication of thin films with remarkably low extrinsic absorption properties with respect to Ion Beam Sputtering. Since there are dimensional and geometric constraints in productions with Ion Beam Sputtering, it is targeted to create an alternative deposition method to exceed these limitations. The primary aim is to investigate and make a comparison of both deposition techniques in producing high-quality optical thin film coatings for near-infrared region. The core of this investigation is the utilization of photothermal common-path interferometry as the primary measurement technique to characterize the deposited thin films. The study initiates with the meticulous assembly and calibration of a specialized photothermal common-path interferometry setup whose configuration is established to measure extremely low sensitive linear absorption in 1064nm wavelength. The working principle of the test system is based on a spatially resolved pump-probe technique. For this reason, it is essential to characterize every component of the test system for highly sensitive measurements. Calibration procedures encompass the validation of the system’s accuracy through bulk and surface calibration samples. After carefully designing the configuration of the system, the sensitivity of our photothermal common-path interferometry test system can reach less than 1 ppm for bulk and 0.1 ppm for surface absorption measurements. The subsequent section involves the application of ion assisted electron beam deposition and ion beam sputtering grown optical thin films. At that point, Ta2O5 and SiO2 thin films were selected as high-index and low-index materials respectively due to their high spectral performances and optical characteristics. Both materials have been grown by each deposition technique. With the optimized deposition parameters, antireflective and high reflective multilayer dielectric coating designs consisting of Ta2O5 and SiO2 alternating layers have been produced. The absorptions of deposited thin films are determined to reach down to a few ppm with both deposition techniques. In addition, the annealing process has been shown to greatly reduce the absorption in both techniques.

Subject Keywords

Photothermal Common-Path Interferometry, Ion Assisted Electron Beam Deposition, Ion Beam Sputtering, Absorption

URI

https://hdl.handle.net/11511/107775

Collections

Graduate School of Natural and Applied Sciences, Thesis