Date of Graduation

2009

Document Type

Dissertation/Thesis

Abstract

An effective use of Nd:YAG lasers in remote, in-situ sensing and other applications require compact size and efficient operation. Our prior work demonstrated that a functioning Nd:YAG laser resonator could be reduced to the size of approximately 1cm2 (10mmx12mm) and 2mm thickness with an output power of 2.2W and an efficiency of 6%. Enhancing the efficiency and output energy and further reducing the size of these slab lasers will make them attractive candidates for compact laser sources in applications such as Laser Induced Breakdown Spectroscopy (LIBS), laser-based spark plug systems, and Raman excitation-based integrated sensor systems. This dissertation targets the design and realization of an Nd: YAG mini slab laser system of smaller volume and shorter cavity size which can be Q-switched and frequency doubled to 532nm. Each system function is experimentally confirmed in an optical bench top configuration. Optimal approaches are then transferred to a hybrid-integrated test bed and assessed for achieving these functions in a compact configuration. This work includes experiments with a rectangular slab whose dimensions were reduced to 5mmx11mm and 2.5mm thickness that resulted in successful single output mode lasing at 1064nm in pulsed pump excitation mode. Also, results with the experimental setup and layout of the mini slab, diode laser array, and rod lens to better couple the pump energy to the lasing mode, development of a compact diode pump laser driver, and integration of a test substrate to mount rod lens, diode bar and minislab are evaluated. The system optimization, characterization and validation are undertaken. This includes the incorporation of the passive Q-switch for high peak powers and non linear crystal for frequency doubling, and strategies for their hybrid integration in a single substrate with the laser slab. A performance assessment is performed and limitations imposed by the hybrid integrated system leading to a new Brewster angle configuration are addressed. The developed green laser system is tested for Raman excitation to detect natural gas and its constituents. Subsequently, the testing results compared with a commercial laser system are also presented. Finally a fast sensor system for fuel gasses based on Raman spectroscopy is presented. An internally silver coated capillary is used as the sample cell and as the optical collection device to extend the sample interaction-length and collect a large Raman scattering signal. A sharp cut-off, long-pass dichroic mirror and a notch rejection filter permit use of a single monochromator with a cooled array detector to monitor the spontaneous Raman Stokes signal at frequency shifts less than 4400 cm-1. Measurement of methane in a premixed fuel/air burner is presented as an example of the device’s capability.

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