Holographic lens for 532 nm in photo-thermo-refractive glass

Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass are extensively used for laser beam control applications. As planar holographic optical elements, VBGs operate in the entire spectral window of PTR glass transparency - from near UV, through visible, and up to IR spectral regions. However, complex holographic elements, e.g. lenses or curved mirrors, cannot be fabricated in conventional Ce3+ doped PTR glass for applications in the visible spectral region due to its photosensitivity being limited to the UV region. Recently developed PTR glass doped with Tb3+ ions demonstrated sensitivity to visible light. The photo-ionization involves two-step absorption of UV and visible photons via metastable levels of Tb3+. Holograms in this glass were recorded by simultaneous exposure to UV radiation from an LED and visible radiation of the second harmonic from a Nd:YAG laser at 532 nm. For the first time holographic lenses operating at 532 nm were demonstrated in PTR glass. This result paves the way for complex holographic optical elements for operation with high power visible lasers.