Experimental characterization of Cr4+:YAG passively Q-switched Cr:Nd:GSGG lasers and comparison with a simple rate equation model

This thesis presents a study on the comparison and anlysis of a laser rate equation model and the laboratory performance of passively Q-switched microlasers. The laser rate equation model describes the development of a top hat gain distribution taking into account the excited state absorption of the passive Q-switch. The lasers examined are Cr:Nd:GSGG lasers passively Q-switched by a Cr4+:YAG crystal. This work will focus on the performance of these lasers as a function of two key design parameters, the passive Q-switch initial transmission (T0) and laser resonator output coupling (ROC), when values are varied over a wide range. Four lasers, each with unique T0 and ROC values, are studied. Characterization of each laser consists of measuring the energy fluence and duration of the laser pulses. The agreement of these measurements with the calculated values is then analyzed in order to understand the maximum deviation that can be expected from lasers constructed using the simple rate equation model as a design tool. The presented analysis shows that laser pulse fluence measurements deviate from the rate equation model calculations by a maximum of 30% across all measured lasers and that the data fits well to the rate equation calculated fluence values. The agreement of the calculated pulse duration estimates with the experimental data is less successful. The measured data deviates from the calculated values by as much as 90% . The rate equation model consistently overestimates the laser pulse duration, and it does increasingly so for lasers designed with lower ROC and larger T0 values. The data presented shows that a simple rate equation model to be used as a laser design tool is useful in developing preliminary designs for low-order transverse mode lasers. However, care should be exercised when a precise understanding of the laser pulse duration is required.University of New Mexico. Optical Science and Engineering Program