Triple overwritten Bragg gratings based multiwavelength distributed feedback dye laser

Emission of multiple laser lines spectra due to three overwritten dynamic Bragg gratings in solution of Rhodamine 6G in ethanol is reported. The overlaid gratings were produced on dye solution by interference patterns of three pairs of frequency doubled Nd:YAG laser. Convolution of three dynamic overwritten gratings with different periodicities gave rise to generation of nine gratings of different periods in the interaction region. Additional gratings induced by interaction of three main overlaid gratings were found to satisfy the Bragg scattering conditions to cause simultaneous laser action at multiple wavelengths. Maximum number of laser lines depends upon the delay between the adjacent pairs of the main pumping beams and their number. For one, two and three pairs of excitation beams, derived from the same source through wave front or amplitude phase division techniques, the output lasing lines varied from 1, 5 and 9 respectively. These findings suggest a quite distinct way of generating coherent continual spectra. This work was carried out by pumping dye solution with maximum six pulses to generate 5.4 nm wide discrete supercontinuum; consisting of nine distinct coherent lines, but the principle may be extended to higher order spectral range; depending upon the available gain medium and number of pumping pulses.