Filtration System for Broad Frequency Laser Emissions

Abstract

This report describes the design of a laser filtration and frequency locking system. The purpose of this system is to facilitate Rayleigh scattering by eliminating broad frequency emissions from a Sacher TEC-500-765-10 External Cavity Diode Laser that have been interfering with the reading and analysis of the Rayleigh scattering off of the main beam of that same laser. Two designs were developed and are presented here. Both designs use a PID loop and an etalon in order to achieve the design goals. Design I modulates the angle of a Fabry-Perot etalon in order to shift the transmission curve of the etalon until it locks onto the main frequency of the laser, thus eliminating the extraneous broad frequency emissions. This design could not be fully tested due to inadequate hardware; however, preliminary testing indicated it was a viable design. Design II differs from Design I in that it modulates the laser frequency instead of the etalon. The laser frequency actually locks onto the etalon transmission curve, instead of the reverse. Design II was tested successfully. This report will describe these designs in greater detail, and discuss the testing results for each design. Finally, we will outline the next steps in incorporating one of these two systems into the Rayleigh scattering experiment, including difficulties that we anticipate and possible courses of action.