Comparative Analysis of Birefringent Tuning Devices for Dye Lasers.

Lasers can be made using organic dyes as the lasing medium. The output signal for such a laser covers a large spectral range. When a frequency selective device is inserted in the lasing cavity, the output signal can be narrowed without loss of output power. If the passband of the intracavity device is variable a tunable laser can be produced. In search of a simple highly-transparent tuning device, four birefringent filters using various tuning techniques have been analyzed and compared. Three of the filters use a combination of linear polarizers and retardation plates to produce a tunable output. The fourth device, called a tilted plates filter, uses only retarders. The retarders are inserted in the lasing cavity at Brewsters angle so as to form a partial polarizer. The criteria used for comparing the devices are insertion loss, resistance to optical damage, and simplicity. All of the filters are satisfactory with respect to optical damage having a damage threshold on the order of 1 gigawattsq cm. WIth respect to the other two criteria, the tilted plates filter is found to be superior. To produce a filter with a 10A lasing bandwidth and a 600A tuning range, two retarders are required. For tuning, these retarders are rotated so as to maintain the Brewster angle orientation with the laser axis. The insertion loss for the tilted plates filter is only 0.04 per pass when the filter is made using calcite and 2.3 per pass when quartz is used. The thin crystals required render a calcite filter impractical. Author