Being able to survey the sky at ultraviolet and near-infrared wavelengths, astronomical spectrographs can study objects almost impossible to see in visible light alone. Very low light intensities of small objects require single-photon sensitivity. The unique optical properties of fused silica, e.g., highest transmission, best homogeneity, and lowest absorption, enable next-generation observations, space-bound as well as earth-bound. However light absorption in the range >800 nm limits the performance of IR spectrographs when using standard fused silica. Metallic impurities and OH groups embedded in the fused silica matrix need to be reduced to achieve best operation. The MOONS camera system at ESO’s Very Large Telescope observes the universe in the NIR range using low OH synthetic fused silica lenses up to a diameter of 900 mm. In the UV spectrum of 160-350 nm, standard fused silica performs in earth-bound systems extremely well. However, in space-bound applications, radiation damage reduces the transmissivity over time. Radiation hard fused silica windows for the PLATO M3 mission of the European Space Agency (ESA) protect the sensitive telescope from damage due to solar protons. Key optical instruments require calibration of the light source to normalize spectroscopic measurements. A radiation resistant fused silica diffusor with Lambertian scattering behavior supports ESA’s Copernicus program in the Sentinel 5 satellite.
Many scientific lasers and increasingly industrial laser systems operate in <500W and kW output power regime, require high-performance optical isolators to prevent disruptive light feedback into the laser cavity. The optically active Faraday material is the key optical element inside the isolator. SYNOPTICS has been supplying the laser market with Terbium Gallium Garnet (TGG - Tb3Ga5O12) for many years. It is the most commonly used material for the 650-1100nm range and the key advantages for TGG include its cubic crystal structure for alignment free processing, little to no intrinsic birefringence, and ease of manufacture. However, for high-power laser applications TGG is limited by its absorption at 1064nm and its thermo-optic coefficient, dn/dT. Specifically, thermal lensing and depolarization effects become a limiting factor at high laser powers. While TGG absorption has improved significantly over the past few years, there is an intrinsic limit. Now, SYNOPTICS is commercializing the enhanced new crystal Potassium Terbium Fluoride KTF (KTb3F10) that exhibits much smaller nonlinear refractive index and thermo-optic coefficients, and still exhibits a Verdet constant near that of TGG. This cubic crystal has relatively low absorption and thermo-optic coefficients. It is now fully characterized and available for select production orders. At OPTIFAB in October 2017 we present recent results comparing the performance of KTF to TGG in optical isolators and show SYNOPTICS advances in large volume crystal growth and the production ramp up.
A novel approach to optical storage based on layering of cholesteric liquid crystal (CLC) media is being pioneered by Reveo, Inc. CLC media have been chosen due to their unique property of selective reflection, wherein a CLC film reflects light of its characteristic wavelength and polarization handedness at near-zero loss while transmitting all other light. The new technology has the potential of making possible Terabyte storage on a single optical disk. This results from the ability to place 2 MN CLC layers on a single disk and reading selectively one or more such layers. Here M refers to the number of `decks' selected by depth- of-focus means. Each `deck' has 2 N layers selected by means of N wavelengths and two polarization states. It is projected that an enhancement factor of 2 MN of 400 is possible for M equals 10 and N equals 20. Furthermore, reading many layers in parallel promises to increase the data rate. The novel concept has been demonstrated in a 6-layer experiment. This, along with computer simulation indicate that the technology is viable and can go to market earlier than other storage technologies.
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