Distributed feedback laser action by polarization modulation

Laser action was generated in dye-doped sol-gel glass waveguides and in liquid solutions by crossing two beams from a frequency-doubled neodymium:YAG laser. The angle between the polarization directions of the two beams was varied continuously from 0-90degrees. The case of 0degrees corresponded to pure intensity modulation. As the angle increased, the degree of intensity modulation decreased, resulting in the decline and finally the demise of the laser output. At 90degrees, corresponding to pure polarization modulation, distributed feedback laser action with narrow line-width output was again observed when the pump energy was increased three-fold. The laser output also showed different polarization characteristics when the feedback mechanism was changed from intensity modulation to polarization modulation.