Scholarship & Research
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Item Digitally automated alignment of a phase-shifting point diffraction interferometer(Montana State University - Bozeman, College of Engineering, 2020) Field, Nathaniel James; Chairperson, Graduate Committee: Joseph A. ShawReal-time sensing of wavefront error in laser instruments is an exceptionally useful tool for fine-tuning of laser systems during fabrication. Measurement and correction for potential wavefront aberrations are especially important for high-energy laser system applications, such as defense and industrial manufacturing. The self-referencing Mach-Zehnder interferometer and the Shack-Hartmann wavefront sensor are two common methods used to achieve real-time wavefront aberration measurements for laser system output quality; however, the former requires a precise and arduous alignment procedure for each operation and the latter exchanges spatial resolution for phase resolution and is highly sensitive to global tilt. The use of electronically controlled spatial light modulators has been shown as a method of quickly retrieving wavefront reconstructions from phase-shifting point diffraction interferometers. In this paper, the development of an algorithm that automates the selection of the point diffractor position and size was added to the phase-shifting point diffraction method with a purely reflective spatial light modulator. Computer simulations and laboratory tests were conducted as proofs of concept using a few simple optical elements. The results of these simulations and lab measurements show promise for continually automated alignment of a point diffraction interferometer to greatly reduce alignment time and almost entirely remove sensitivity to global tilt. With further development, this method can be applied to increase the efficiency of a wide variety of optical system measurement scenarios.Item Applications of high resolution and accuracy frequency modulated continuous wave LADAR(Montana State University - Bozeman, College of Letters & Science, 2014) Baselga Mateo, Ana; Chairperson, Graduate Committee: Wm. Randall BabbittThe high resolution frequency modulated continuous wave (FMCW) laser and detection ranging (LADAR) system developed by Spectrum Lab and Bridger Photonics Inc. could be potentially used for volume metrology purposes. However, comparisons with other length metrology methods would help to determine its actual precision and accuracy. An ultra-low phase noise and narrow bandwidth laser centered at 1536nm is used to build a displacement tracking interferometer for comparisons. Lock-in detection based on phase modulation is used to reduce sensitivity to amplitude noise. The data is processed to obtain an accurate displacement measurement with a novel fringe counting technique that provides resolution higher than lambda/4. After calibrating and figuring out the stability of the FMCW LADAR, its ranging capability is determined by comparison with these results along different wavelength regions. Furthermore, we propose a combination of the trilateration techniques with the FMCW LADAR system for accurate 2D metrology. This idea is developed from design to implementation stages. Surface profiles of non-cooperative diffuse targets using lasers sources with different optical bandwidths are presented. A photon budget and an error analysis of the experimental results are also included.Item Simulating heat generation in the monoblock laser using finite element analysis(Montana State University - Bozeman, College of Engineering, 2011) Anderson, Aaron Paul; Chairperson, Graduate Committee: David A. MillerUnder photonic pumping Nd:YAG (Neodymium Yttrium Aluminum Garnet) generates a significant amount of heat as a result of quantum deficit and non-radiative absorption sites, this excess heat results in thermal deformation and a shift in the index of refraction of Nd:YAG causing a net change in Optical Path Length (OPL). Finite Element Analysis (FEA) techniques provide a powerful approach for digital design and analysis of complex thermo-mechanical systems; unfortunately, finite element software packages do not use light as a traditional loading mechanism nor track optical properties. This research has sought to establish a methodology to interface thermal loading as a result of photonic conversion with traditional FEA practices and track the resulting optical effects. The ABAQUS software package interfaced with a python driven input procedure has been used to develop a representation of photonic loading in the FEA environment. This modeling method has been calibrated utilizing interferometry imaging of a pulsed Nd:YAG system tracking the resultant OPL and comparing these results to FEA predictions. FEA predictions were developed that matched experimental measurements within 0.5 waves at the 1064nm laser line for Nd:YAG.