Volume Bragg Gratings in PTR glass – New Optical Elements for Laser Design Leonid Glebov CREOL, The College of Optics and Photonics, University of Central Florida, P.O. Box 162700, Orlando, Florida 32816-2700 Tel: (407) 823-6983 Fax: (407) 823-6880 Email: lbglebov@creol.ucf.edu Abstract: This is a survey of achievements in semiconductor, solid state and fiber lasers enabled by the use of new optical elements which are volume Bragg gratings recorded in a photo-thermo- refractive (PTR) glass. ©2008 Optical Society of America OCIS codes: (050.7330) Volume holographic gratings; (140.3510) Lasers, fiber. 1. Introduction This paper is a survey of recent achievements at the College of Optics and Photonics/CREOL at the University of Central Florida and at OptiGrate Corporation in the development of diffractive optical elements which are volume Bragg gratings recorded in a photo-thermo-refractive (PTR) glass for dramatic improvement of parameters of different types of lasers demonstrated by a number of different research groups. This new technology enabled recording of high efficiency phase volume holograms in an optical quality silicate glass. These holograms are used for creation of a number of unique diffractive optical elements that provide new opportunities for sensing, signal processing and laser beam control. The same type of glass can be used for design of conventional optical elements and windows working in high power laser beams and under high level of ionizing radiation. Moreover, this material could be used for complex elements creation such as all-solid-state lasers and combined refractive and diffractive elements. Multiple conventional photosensitive materials for volume hologram recording have its own merits, combined with considerable drawbacks [1]. Finally, none of those materials had a combination of high phase sensitivity, low loses and high tolerance to laser radiation which are necessary for wide application in laser design. Availability of diffractive optical elements fabricated from PTR glass changed the situation. 2. Photo-thermo-refractive glass The history of the study of photo-thermo-refractive process and its parameters from the point of view of hologram recording were summarized in surveys [2, 3]. Recent improvements of PTR technology [4, 5] resulted in creation of volume phase holograms (Bragg gratings) with low losses and extremely high diffraction efficiency exceeding 99%. PTR glass is a Na 2 O-ZnO-Al 2 O 3 -SiO 2 glass doped with silver, cerium, and fluorine. The window of transparency ranges from 350 to 2700 nm. Thermal variations of refractive index in PTR glass are very low (dn/dT=5×10 -8 1/K). The maximum value of the refractive index decrement after exposure to UV radiation and thermal development is about 10 -3 . The photosensitivity of PTR glass for 325 nm irradiation followed by 3 hours of development at 520 o C is 1.5×10 -3 cm 2 /J which means that a standard dosage for high efficiency hologram recording does not exceed few hundreds of mJ/cm 2 . That fact that refractive index modulation in PTR glass is resulted from thermal precipitation of a crystalline phase, leads to an important consequence. There is no way to destroy crystalline particles of NaF in glass matrix by any type of radiation. This is why PTR holograms are stable under exposure to IR, visible, UV, X- ray, and gamma-ray irradiation. 3. Volume Bragg gratings Bragg gratings in PTR glass were mainly recorded by an exposure to the interference pattern of radiation of He-Cd laser operating at 325 nm with average power of 35 mW. Spatial frequency of gratings was varied from 50 to about 10,000 mm -1 . Volume gratings in both transmitting and reflecting mode were recorded with thickness ranged from 0.5 mm to 25 mm. Both transmitting and reflecting gratings could be tilted inside a glass wafer for almost arbitrary angles. Maximum aperture of gratings was up to 50 mm×50 mm. Diffraction efficiency was measured at different wavelengths ranged from 355 to 2000 nm. In all cases, maximum absolute diffraction efficiency of PTR Bragg gratings exceeded 95 % while relative diffractive efficiency was demonstrated above 99.9%. Detailed mathematical modeling of transmitting PTR Bragg gratings is presented in Ref. [6]. Angular selectivity MD1.pdf © 2008 OSA/ BIOMED/DH/LACSEA 2008 MD1.pdf © 2008 OSA/ ASSP MD1.pdf