Mode structure of a DFB gas laser

Experiments are described whose aim is to confirm DFB mode equations which show that a variation of the period, the waveguide height, or the width changes the DFB mode. A second aim is to avoid excitation of transverse modes for an index of the longitudinal DFB modes equal to about zero. The waveguide temperature of an optically pumped 496 micron CH3F DFB laser was varied in order to modify the length and the period, permitting observation of two adjacent fundamental DFB modes for a temperature variation of 42 K. The laser exhibited the predicted dependence of output on length of the structure period. Changing the waveguide cross section permitted proper DFB operation to be achieved in the fundamental longitudinal modes even at the center of the Bragg resonance.