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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 Development of an active/adaptive laser scanning microscope(Montana State University - Bozeman, College of Engineering, 2018) Archer-Zhang, Christian Chunzi; Chairperson, Graduate Committee: David L. DickensheetsLaser scanning techniques such as confocal microscopy and two-photon excitation fluorescence microscopy (TPM) are powerful tools for imaging biological samples with high resolution, offering three-dimensional (3D) visualization of the behavior of cells in their natural environment. Traditionally, the 3D images are acquired from 2D image stacks with focusing depth controlled through mechanical movement of the specimen relative to the objective lens. The slow mechanical movement (~<20Hz) does not allow the spot of light to be scanned axially sufficiently fast to monitor cell:cell and cell:environment interactions in real time over hundreds of microns in all three dimensions. A fast focus control mirror supports agile scan patterns such as vertical or oblique planes or even arbitrary surfaces, minimizing the time and photo damage required to monitor features of interest within the 3D volume. Because aberrations cause image quality to decrease as the focal point of the beam penetrates deeper into the sample, adaptive optics can enhance resolution and contrast at depth for confocal microscopy and TPM. Combining a fast focus control mirror with a fast aberration correcting mirror leads to a flexible platform called the active/adaptive laser scanning microscope, capable of aberration-corrected beam scanning throughout a 3D volume of tissue. This opens up the possibility of fully corrected, variable-depth imaging along oblique sections or more complex user-defined surfaces within a single image frame.Item Silicon nitride deformable mirrors for focus and spherical aberration correction in micro-optical systems(Montana State University - Bozeman, College of Engineering, 2002) Himmer, Phillip Alexander; Chairperson, Graduate Committee: David Dickensheets.Laser beam scanning systems benefit from dynamic focus control and aberration correction using a deformable mirror, enabling 3D real-time scanning. Designed for focus and spherical aberration control in optical beam scanning systems, these mirrors are capable of video rate bandwidths allowing real-time 3D imaging in micro-optical scanning systems. Field curvature aberration can also be corrected with the same mirror. Previous work with polysilicon deformable mirrors validated the concept of using specialized deformable optics in beam scanning systems. Fabrication of micro-optics in this dissertation was achieved using a modified surface micromachining technique with silicon nitride replacing polysilicon as the structural material. A bulk anisotropic silicon etch following a PSG release etch allows the creation of a variable cavity depth, overcoming the typical deformation limitations of standard surface micromachining. To perform as desired, parabolic curvature of the mirror surface is required with the ability to introduce positive and negative quartic curvature. Analytical theory showed that deformed simply supported plates have curvature closer to parabolic than deformed clamped plates. Segmentation and thinning of the perimeter was done to in order to emulate this simply supported boundary. Two annular actuation zones were implemented to give independent control over the second and fourth order curvatures. It was found that residual stress present in the silicon nitride structural plate improved the surface curvature and mechanical resonance at the expense of a larger actuation pressure. Mirrors with diameters of 1500, 1000, 750, and 300 microns were built and tested. Zonal actuation with annular electrodes proved successful in providing sufficient correction of the mirror surface curvature, allowing spherical aberration free focus control. Perimeter segmentation greatly reduced required actuation loads allowing improved focal ranges. It was found that the sacrificial layer thickness has a significant impact on the initial curvature of the mirror. Sacrificial layers 0.2 microns thick proved sufficient for release, improved device yield, and resulted in an initially flat mirror.Item Development of an eye-safe diode-laser-based micro-pulse differential absorption lidar (mp-DIAL) for atmospheric water-vapor and aerosol studies(Montana State University - Bozeman, College of Engineering, 2011) Nehrir, Amin Reza; Chairperson, Graduate Committee: Kevin S. RepaskyThis dissertation describes the design, construction, and testing of an all diode-laser-based water-vapor differential absorption lidar (DIAL) instrument through two distinct stages of development. A second generation low pulse energy, high pulse repetition frequency DIAL instrument was developed to overcome the power limitations of the first generation instrument which required unrealistic integration times approaching 1 hour. The second generation DIAL transmitter used a custom built external cavity diode laser (ECDL) as the seed source for an actively current pulsed tapered semiconductor optical amplifier (TSOA), yielding a maximum output transmitter pulse energy of 2 microjoules over a 1 microsecond duration pulse width at a 20 kHz pulse repetition frequency, decreasing the required integration Period to approximately 20-30 minutes. Nighttime and daytime water-vapor profiles were collected with the second generation DIAL instrument which showed good agreement with collocated radiosonde measurements from near the surface up to the top of the planetary boundary layer. Aerosol optical properties were also measured using the calibrated offline channel returns using the iterative Fernald solution to the lidar equation. Most recently, a third generation DIAL transmitter has been developed to further increase the output pulse energy and to also decrease the DIAL atmospheric spectral sampling time. Two custom built high power ECDL's and an electro-mechanical based fiber optic switch are used to sequentially seed a single stage actively current pulsed TSOA in order to minimize the systematic errors introduced in the DIAL retrievals resulting from air-mass miss-sampling between the two DIAL wavelengths. Peak output pulse energies of 7 microjoules have been measured over 1 microsecond pulse durations at a 10 kHz pulse repetition frequency with a 1-6 second DIAL spectral switching time, further decreasing the total required integration period to 20 minutes for both nighttime and daytime operation. The increased performance of the third generation transmitter has allowed for nighttime and daytime water vapor profiling under varying atmospheric conditions that shows good agreement with collocated radiosonde measurements up to ~ 6 km and ~ 3 km, respectively. A detailed description of the second and third generation DIAL instrument performance as well as data retrievals are presented in this dissertation. Future work to improve the current third generation DIAL instrument for full-time autonomous measurements of atmospheric water-vapor and aerosols is also discussed.Item Carbon dioxide sequestration underground laser based detection system(Montana State University - Bozeman, College of Engineering, 2009) Barr, Jamie Lynn; Chairperson, Graduate Committee: Kevin S. Repasky; John L. Carlsten (co-chair)Carbon dioxide (CO 2) is a known greenhouse gas. Due to the burning of fossil fuels by industrial and power plants the atmospheric concentration of CO 2 has been rising over the past 50 years. Carbon capture and sequestration provides a method to prevent CO 2 from being emitted into the atmosphere. Successful carbon sequestration will require the development of many pieces of technology including development of monitoring tools and techniques. An underground laser based monitoring system was built and tested at Montana State University (MSU) to measure sub-surface CO 2 concentrations at a sequestration site. The instrument uses differential absorption spectroscopy by temperature tuning a distributed feedback diode laser over several CO 2 absorption features located at 2.004 microns. The instrument utilizes photonic bandgap fibers for sub-surface spectroscopy CO 2 concentration measurements. The instrument was tested at a controlled release facility located on the MSU campus. The field and CO 2 release are managed by the Zero Emissions Research and Technology group at MSU. Three CO 2 injection tests were done over the coarse of two summers to simulate a fault or fracture line at a sequestration site. Results from all three tests are presented showing that the underground differential absorption instrument could be used to monitor sequestration sites.Item Compact, mid-infrared laser source for remote sensing of gas effluents(Montana State University - Bozeman, College of Engineering, 2009) Berg, Trenton Jeffery; Chairperson, Graduate Committee: Joseph A. ShawRemote sensing of gas effluents in the mid-IR wavelength region from 2 microns to 5 microns is preferred due to strong molecular absorption features (10 to 100 times stronger than in the near-IR) and high-transparency atmospheric windows. Currently, long-range mid-IR remote sensing is inhibited by the lack of suitable laser sources. As a result, frequency conversion in nonlinear optical materials has emerged as a powerful method to produce high-power, tunable, mid-IR light. However, compact, high-power narrowband conversion systems suitable for long-range mid-IR spectroscopy are not commercially available. This thesis describes the development of a high-power, narrowband, tunable, compact, mid-IR laser source for long-range remote sensing of gas effluents. Frequency conversion into the mid-IR is achieved by use of a high-peak-power, compact pump laser and optical parametric generation (OPG) in periodically poled nonlinear crystals. This mid-IR laser system was designed and developed for remote sensing at ranges up to and exceeding 100 m in a compact form factor. Such a laser will fill the current scientific need for a hand-held mid-IR laser source capable of long-range mid-IR spectroscopy. Based on theoretical models and experimental demonstrations a compact mid-IR laser source was developed that emits > 1 mJ broadband pulses in the mid-IR. To narrow the linewidth of the broadband OPG output, optical parametric amplification was demonstrated through seeding of the OPG process with a narrowband, continuous-wave, distributed feedback (DFB) laser. Seeding efficiencies exceeding 35% were demonstrated for 1 mJ of output energy, and efficiencies exceeding 65% were demonstrated at lower energies when the pump beam was spatially filtered. The linewidth of the narrowed mid- IR output was inferred to be < 350 MHz based upon heterodyne measurements conducted at the signal wavelength in the near-IR. This linewidth is well within the FWHM bandwidth of typical mid-IR atmospherically broadened molecular absorption features. The demonstrated mid-IR energies and laser linewidths are predicted to be sufficient for detection of low concentration gas effluents (< 1 ppm) at ranges exceeding 100 m. The developed mid-IR laser source was used to successfully demonstrate differential detection of carbon dioxide (CO 2).