Volume Bragg lasers

This paper is a survey of recent achievements at the College of Optics and Photonics/CREOL at the University of Central Florida in the use of newly developed diffractive optical elements which are volume Bragg gratings recorded in a photo-thermo-refractive (PTR) glass. Three levels of semiconductor laser design are proposed to achieve high-power low-divergence output. The first level is coherent coupling of emitters by means of PTR Bragg gratings which provide excitation of only one common mode in a multichannel resonator. This type of phase locking automatically leads to a narrow spectral width of emission usually not exceeding a few tens of picometers. The second level is a change of the mechanism of transverse mode selection from spatial selection by apertures to angular selection by PTR Bragg gratings. This approach allows increasing of the aperture size without increasing the length and selecting of arbitrary mode but not necessarily a fundamental one. The third level is spectral beam combining by PTR Bragg gratings which re-direct radiation from several high-power fiber lasers to co-propagate in the same direction with diffraction limited divergence. This approach allows simplification of the thermal management because only passive devices with low absorption (a PTR volume Bragg gratings) are placed in the path of high power laser beam.