Planar holographic optical elements (volume Bragg gratings, VBGs) recorded in photo-thermo-refractive (PTR) glass are widely used for fine spectral filtering and laser beam control. PTR glass provides photosensitivity in near UV region. Therefore, while planar holographic elements operate in the whole window of transparency - near UV, visible and near IR spectral regions, application of complex (nonplanar) elements is restricted to near UV. A method has been proposed to create high-efficiency diffractive optical elements in PTR glass using visible light. The method employs excited state absorption in PTR glass doped with Tb3+. UV radiation was used for excitation to a metastable level of Tb3+ and pulsed radiation at 532 nm was used for hologram recording. Both planar VBGs and holographic lenses operating at 532 nm were demonstrated. Complex holographic optical elements in PTR glass can provide attractive solutions for lasers and spectroscopy replacing conventional optical components.
Photo-thermo-refractive (PTR) glass is a multicomponent silicate glass doped with Ce3+ and Ag+ which is extensively used for holographic recording of volume Bragg gratings (VBGs). Possibility of recording of advanced, complex holograms in the PTR glass is of current interest as it offers great opportunities in imaging and laser systems control. However, the glass does not have capabilities for recording of complex holograms with using light from the visible / IR spectral region due to its UV photosensitivity. Extension of the PTR-glass sensitivity range into the visible / IR spectral region was carried out by doping the original glass with trivalent terbium ions. Photosensitivity mechanism was implemented by means of excited state absorption using a UV photon and a visible photon for excitation of the Tb3+ 5d14f7 band. For the first time refractive index modulation on the order of 2x10-4 was obtained in PTR glass after exposure to the visible / IR light. Resulting magnitude of induced refractive index allows for high efficiency complex hologram fabrication in Tb3+ doped PTR glass for use which in the visible / IR region. Holographic capabilities of Tb3+ doped PTR glass were demonstrated by recording a complex hologram in the glass using green and blue light.