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.
Eu-doped strontium iodide single crystal growth has reached maturity and prototype SrI2(Eu)-based gamma ray
spectrometers provide detection performance advantages over standard detectors. SrI2(Eu) offers a high, proportional light
yield of >80,000 photons/MeV. Energy resolution of <3% at 662 keV with 1.5” x 1.5” SrI2(Eu) crystals is routinely
achieved, by employing either a small taper at the top of the crystal or a digital readout technique. These methods overcome
light-trapping, in which scintillation light is re-absorbed and re-emitted in Eu2+-doped crystals. Its excellent energy
resolution, lack of intrinsic radioactivity or toxicity, and commercial availability make SrI2(Eu) the ideal scintillator for
use in handheld radioisotope identification devices. A 6-lb SrI2(Eu) radioisotope identifier is described.
Development of the Europium-doped Strontium Iodide scintillator, SrI2(Eu2+), has progressed significantly in recent years. SrI2(Eu2+) has excellent material properties for gamma ray spectroscopy: high light yield (<80,000 ph/MeV), excellent light yield proportionality, and high effective atomic number (Z = 49) for high photoelectric cross-section. High quality 1.5” and 2” diameter boules are now available due to rapid advances in SrI2(Eu) crystal growth. In these large SrI2(Eu) crystals, optical self-absorption by Eu2+ degrades the energy resolution as measured by analog electronics, but we mitigate this effect through on-the-fly correction of the scintillation pulses by digital readout electronics. Using this digital correction technique we have demonstrated energy resolution of 2.9% FWHM at 662 keV for a 4 in3 SrI2(Eu) crystal, over 2.6 inches long. Based on this digital readout technology, we have developed a detector prototype with greatly improved radioisotope identification capability compared to Sodium Iodide, NaI(Tl). The higher resolution of SrI2(Eu) yields a factor of 2 to 5 improvement in radioisotope identification (RIID) error rate compared to NaI(Tl).