Recording Of Robust Holographic Optical Elements In Glass

This is a survey of recent results achieved with an inorganic material for volume holographic optical elements which is more efficient and robust than alternative materials. It is a photo-thermo-refractive (PTR) glass in which Bragg gratings (holograms) can be written in the interior (not the surface) of the glass. PTR glass is transparent from 350 to 2700 nm. It is a crown-type optical glass having refractive index at 587.5 nm nd=1.4959 and Abbe number vd=59.2. This glass shows low dependence of refractive index on temperature dn/dt\u3c10-6 1/K. PTR glass has the same nonlinear refractive as fused silica. Refractive index in PTR glass decreases for 1000 ppm after UV exposure and thermal development. An approximate value of the photosensitivity is Δn/E=1.5×10-3 cm2/J. Laser damage threshold is 40 J/cm2 for 8 ns laser pulses at 1064 nm. Glass is stable in multi-kilowatt CW laser beams. Novel volume diffractive gratings have been made including exceptionally narrow band transmitting and reflecting elements. This technology is used to make diffractive elements such as spatial filters, attenuators, switches, modulators, beam splitters, beam samplers, beam deflectors, selectors of particular wavelengths (notch filters, add/drop elements), spectral shape formers (gain equalizers), spectral sensors, angular sensors, Bragg spectrometers, transverse and longitudinal mode selectors in a laser resonator, and wavelength tuners and stabilizers for different lasers. Combinations of the above listed elements can be made within the same piece of glass. High power semiconductor and solid state volume Bragg lasers oscillating in single transverse mode with spectral width below 50 pm are demonstrated