Photo-thermal-sensitive Characters And Reflective Index Variation Of PTR Glass

With the application of laser and communication in optical system, one of the new approaches to the optical system utilizing the narrow-band lasers, is the use of diffractive optical components including such very promising elements as volume diffractive (or Bragg) gratings. However, traditional gratings materials have rather low laser damage threshold, which cannot satisfy the high power lasers system. Furthermore, large surface volume grating is difficult to be made by traditional grating materials. The PTR (Photo-Thermo-Refractive) glass is a kind of grating materials with high laser damage threshold, which could be made volume grating conveniently.Na-Zn-Al-Si is chosen as a fundamental glass system, Ce3+and Ag+as photo-sensitizer, also added a little Sb2OE and SnO2as thermal-sensitizer. We melted the glass at1450℃for4-5hours. We optimized glass formula based on experimental results. Then, taking samples with difference exposure and thermal development, we test glass property by several ways including EDS, DSC, spectroscopic transmittance, X-ray diffraction analysis, scanning electron microscope map analysis and reflective index variation.Glass photosensitive characters will be good by proper exposure and heat treatment in abundant experiments. The most optimum exposed wavelength of the PTR glass is305nm because the Ce3+is sensitive for it. And the exposure dosage was controlled by exposure time. The temperature of thermal development was confirmed by DSC and the temperature range are460～520℃and500～560℃. The treated glasses were tested by spectroscopic transmittance in400nm-2800nm, and its transmittance reaches80%. NaF microcrystal was formed inside after the glass was treated (exposure and heat treatment) by XRD. With SEM map of treatment PTR glass, the particle size of the microcrystal is about0.3-0.8nm. Then, the reflective index variation and its method were studied. The mach-zender interference was chosen be compared other methods. The test samples were process and their cross sections as test face were cut and polished, the reflective index variation was test about10-4. Finally, the diffraction efficiency, spectral and angel selectivity of volume Bragg gratings were studied by theory and simulation, which can afford assistance for high power laser filter.Experimental results showed that PTR glasses have good photo-thermal character, high transmittance between visible-infrared wavelengths and optimum performance. It can be used for making volume Bragg grating. Therefore, PTR glass is an attractive material for making volume Bragg grating.