Energy Monitoring and Control of Harmonic Generators for Lidar Application
Document ID: 112
Master's Thesis
The Pennsylvania State University
The Graduate School
Department of Electrical Engineering
Abstract
This thesis presents the design and development of a laser energy monitor which accomplishes the task of continuously measuring the laser's pulse energy and providing information for the tuning of harmonic generating crystals. The new energy monitor demonstrates its usefulness in a lidar system developed at Penn State for continuous use onboard Navy ships. However, the goal was also to design a simple and cost-effective device that could be useful in several other applications.
The energy monitor accomplishes simultaneous measurements of a laser's power at two harmonic frequencies. Volume scattering in a glass window as the beam passes through provides a simple means of obtaining a constant fraction of the laser's energy per pulse. A peak detector circuit changes the pulsed signal to a DC signal that is linearly proportional to the laser's power. This measurement both characterizes the laser's performance and allows an automatic control sequence to "peak" the harmonic generators. The designed control system will optimize these harmonic generators one at a time with a modified gradient, adaptive step size algorithm. Simulation software offers a good environment for modeling the oddities of a particular harmonic generator and for testing the control algorithm.
The energy monitor and control designs were driven by requirements of the LAPS (Lidar Atmospheric Profile Sounder) system. Final results verify the proper operation of the energy monitor and suggest its usefulness in other applications. Also, the tuning of the harmonic generators in the LAPS system can be taken as an approach to optimizing other systems that depend upon nonlinear crystals for harmonic generation.
| Citation: | S. O. Sprague, "Energy Monitoring and Control of Harmonic Generators for Lidar Application", The Pennsylvania State University, Master's Thesis, May 1995, 60 pages |