Theses and Dissertations at Montana State University (MSU)
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Item Transient passive mode-locked ND:YAG laser using a semiconductor saturable absorber mirror(Montana State University - Bozeman, College of Letters & Science, 2022) Shaffer, Heather Rose; Chairperson, Graduate Committee: Joseph A. ShawQ-switched-mode-locking in a Nd:YAG bulk resonator was demonstrated using a semiconductor saturable absorber mirror (SESAM). A 10-W-pulsed-diode-pumped Nd:YAG laser system at Quantel USA by Lumibird, Inc. was adapted for mode-locking operation in a breadboard setup. Three SESAM mirrors were tested with initial reflectivities R 0=85%, 90%, and 95% in several cavity configurations to show enhanced sub-nanosecond pulse modulation at the free spectral range of each resonator. Transient Q-switched and long-pulse envelopes are shown with underlying mode-locked pulse modulation.Item MEMS 3-dimensional scanner with SU-8 flexures for a handheld confocal microscope(Montana State University - Bozeman, College of Engineering, 2018) Liu, Tianbo; Chairperson, Graduate Committee: David DickensheetsThe conventional method for diagnosing skin cancer is to perform a biopsy followed by pathology. However not only are biopsies invasive and likely to leave permanent scarring, they also sample the body sparsely. Fortunately, a non-invasive method of imaging called confocal laser scanning microscopy has shown great potential to replacing invasive biopsies. Confocal microscopy can use light to achieve high-resolution imaging of cells that lie underneath the surface of the skin. However, the large size of current confocal microscopes limits their application to all but the most accessible sites. In this dissertation, I address the miniaturization of confocal microscopy through the development of a new microelectromechanical systems scan mirror that can scan a focused beam in three dimensions. The scanner has a 4 mm aperture, and has the capability to replace all of the bulky beam scanners and focus mechanisms that contribute to the large size of current confocal microscopes. The fabrication of the scanner explores the use of the polymer SU-8 for its mechanical structures. The gimbal mirror has demonstrated scan angles in excess of plus or minus 3° mechanical for lateral scanning, and its deformable surface provided controllable deflection up to 10 microns for focus control. This newly developed scanner was integrated into a confocal system to test its imaging capabilities. The device demonstrated high-resolution scanning with simultaneous focus adjustment suitable for the next generation of miniaturized confocal laser scanning microscopes.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 Imaging performance of elliptical-boundary varifocal mirrors in active optical systems(Montana State University - Bozeman, College of Engineering, 2015) Lukes, Sarah Jane; Chairperson, Graduate Committee: David L. DickensheetsMicro-electro-mechanical systems deformable-membrane mirrors provide a means of focus control and attendant spherical aberration correction for miniaturized imaging systems. The technology has greatly advanced in the last decade, thereby extending their focal range capabilities. This dissertation describes a novel SU-8 2002 silicon-on-insulator wafer deformable mirror. A 4.000 mm x 5.657 mm mirror for 45° incident light rays achieves 22 micron stroke or 65 diopters, limited by snapdown. The mirrors show excellent optical quality while flat. Most have peak-to-valley difference of less than 150 nm and root-mean-square less than 25 nm. The process proves simple, only requiring a silicon-on-insulator wafer, SU-8 2002, and a metal layer. Xenon difluoride etches the silicon to release the mirrors. Greater than 90% of the devices survive fabrication and release. While current literature includes several aberration analyses on static mirrors, analyses that incorporate the dynamic nature of these mirrors do not exist. Optical designers may have a choice between deformable mirrors and other types of varifocal mirrors or lenses. Furthermore, a dynamic mirror at an incidence angle other than normal may be desired due to space limitations or for higher throughput (normal incidence requires a beam splitter). This dissertation presents an analysis based on the characteristic function of the system. It provides 2nd and 3rd order aberration coefficients in terms of dynamic focus range and base ray incidence angle. These afford an understanding of the significance of different types of aberrations. Root-mean-square and Strehl calculations provide insight into overall imaging performance for various conditions. I present general guidelines for maximum incidence angle and field of fiew that provide near diffraction-limited performance. Experimental verification of the MEMS mirrors at 5° and 45° incidence angles validates the analytical results. A Blu-ray optical pick-up imaging demonstration shows the utility of these mirrors for focus control and spherical aberration correction. Imaging results of the first demonstration of a deformable mirror for dynamic agile focus control and spherical aberration correction in a commercial table-top confocal microscope are also shown.Item Silicon nitride membrane mirrors for focus control(Montana State University - Bozeman, College of Engineering, 2001) Friholm, Robert AndreasItem Large-stroke deformable MEMS mirror for focus control(Montana State University - Bozeman, College of Engineering, 2013) Moghimi, Seyyed Mohammad Javad; Chairperson, Graduate Committee: David L. DickensheetsWe developed a novel large-stroke deformable mirror for focus control and spherical aberration correction. The mirrors fabricated using MEMS technology provide full range (150-200 microns in tissue) of focus scanning at high numerical aperture (N.A.=0.5-0.7) for confocal microscopy and optical coherence tomography (OCT). In addition to large stroke, low power consumption and high speed operation are other key factors of the developed devices. The impact of this project is broad since the miniaturized deformable mirrors have a wide range of applications. In addition to focus scanning in microscopes they can also be used in small form factor systems such as cell phone cameras and robot vision. Furthermore, laser based microscopes equipped with the focus control mirror may be useful for skin cancer diagnosis and treatment. This thesis consists of seven chapters. The first chapter introduces optical focus control and focus control elements. The second chapter describes different schemes for optical focus control in imaging systems including transmissive variable lenses. The principle of operation, fabrication, and characterization of electrostatic deformable mirrors are reviewed in Chapter 3. High-speed focus control mirrors with controlled air damping are discussed in Chapter 4. In this chapter a model adopted from the analysis of MEMS microphone is used to design the backplate of a MEMS deformable mirror. Moreover, electrostatic-pneumatic MEMS deformable mirrors are introduced in Chapter 5. Analytical model is developed for electrostatic-pneumatic actuation in order to design a MEMS mirror with two membranes. Applications of MEMS deformable mirrors are demonstrated in optical systems in Chapter 6. Finally, a summary and future work are discussed in Chapter 7. The fabrication process details are given in Appendix A.Item Numerical modeling of the deflection of an electrostatically actuated circular membrane mirror(Montana State University - Bozeman, College of Engineering, 2011) Moog, Eric John; Chairperson, Graduate Committee: Steven R. Shaw; David L. Dickensheets (co-chair)This thesis outlines a numerical modeling method to describe the deflection behavior and investigate control schemes for an electrostatically actuated deformable membrane mirror, with application to focus control and aberration correction in micrelectromechanical systems. The physics of the membrane are approximated using a finite difference approach with parameters obtained from measurements of a physical device. The model is validated by comparison of simulated and measured mirror position under static and dynamic conditions. This thesis provides simulation results for control schemes that would be difficult or potentially destructive if implemented using real devices. We suggest that the model may be useful for the development of future control strategies and in refining device design. Finally, a number of capacitive sensing circuits are presented as position feedback mechanisms and the capabilities and limitations of each are examined.