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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

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 (

Crystal structures with varying degrees of disorder have been grown by the Czochralski method. Examples include SrGdGa 3 0 7 (SGGM), La 3 Ga 3 SiO l4 (LGS), La 3 Ga 5 GeO 14 (LGG), CaLa 4 (SiO 4 ) 3 0 (CaLaSOAP), CaY 4 (SiO 4 ) 3 0 (CaYSOAP) and Y 2 SiO 5 (YOS). Crystals were doped with Nd, Tm and Er for spectroscopic evaluation. Nd: SGGM is a promising material for diode pumping because the 808 nm absorption linewidth is an order of magnitude larger than Nd:YAG.

The laser is nearing completion with demonstration of 73% frequency-conversion efficiency, deformable mirror operation that generated a 4-times diffraction limited spot, and commissioning of an advanced front end to be installed on the main laser.

We report initial operation of the Mercury laser with seven 4 x 6 cm S-FAP amplifier slabs pumped by four 80 kW diode arrays. The system produced up to 33.5 J single shot, 23.5 J at 5 Hz, and 10 J at 10 Hz for 20 minute runs at 1047 nm. During the initial campaign, more than 2.8 x 104 shots were accumulated on the system. The beam quality of the system was measured to be 2.8 x 6.3 times diffraction limited at 110 W of output, with 96% of the energy in a 5X diffraction limited spot. Static wavefront glass plates were used to correct for the low order distortions in the slabs due to fabrication and thermal loading. Scaling of crystal grown has begun with the first full size slab produced from large diameter growth. Using an energetics optimization code we find the beam aperture is scalable up to 20 x 30 cm and 4.2 kJ.

The growth of Yb:S-FAP [Yb3+:Sr5(PO4)3F] crystals is being developed for use as the gain medium in the Mercury Laser, a gas-cooled amplifier system intended to yield 100J, 10Hz and 10% efficiency in 3 nsec when completed, for inertial fusion energy. A number of defect issues have been overcome to produce high quality crystals, including: cloudiness, bubble core defects, anomalous absorption, low-angle grain boundaries, cracking, and crystal inclusions. Currently useful crystals are routinely produced for fabrication into full size slabs. However, stress cracking during fabrication is being addressed as a critical issue in producing the 14 slabs necessary for full activation of the Mercury Laser.

A new reflected mode magneto-optic spatial light modulator (R-MOSLM) has been developed for miniature optical correlators and computers. An improvement by a factor of four in pixel switching sensitivity, compared to the conventional transmission mode magneto-optic spatial light modulator (T-MOSLM), has been achieved by the use of narrower drive lines, and burying the conductor into the film. A higher resolution by a factor of three and a higher optical efficiency by a factor of two have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively. >

This paper is a report on the characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of Miniature Ruggedized Optical Correlators for Optical Pattern Recognition. Pixel size is under one mil center to center, one-third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems.

This paper is a report on the advanced development and characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of miniature ruggedized optical correlators (MROC) for optical pattern recognition. Pixel size is under one mil center to center, one third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems. The device research and process development has been performed at Carnegie Mellon University NSF Data Storage System Center under contract from Litton Data Systems. The Litton Electron Device Division is transitioning the device to production. The MROC system description is described in companion paper (1959-09).

Single crystals of three Nd3+-doped disordered oxides have been grown and characterized as candidates for improved diode-pumped solid state lasers. These hosts include one melilite, SrGdGa3O7 (SGGM), and two gallogermanates, La3Ga5GeO14 (LGG) and its isomorph La3Ga5SiO14 (LGS). Spectroscopic properties such as absorption and emission bandwidth, fluorescent lifetimes, and emission cross-sections are included. Laser properties of the 4F3/2 - 4I11/2 transition at 1.06 microns have been measured.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The interest in diode pumped solid state lasers in the 2 μm region in recent years has been well documented. The need for compact, highly efficient sources has led to the study of new laser hosts which may improve performance. We have grown and analyzed the spectroscopic properties of two Tm3+-doped silicate oxyapatite hosts and one orthosilicate. These hosts are CaY4(SiO4)3O [CaYSOAP], CaLa4(SiO4)3O [CaLaSOAP], and Y2SiO5 [YSO or YOS]. The spectroscopic properties of these new hosts are compared with those of Tm3+:YAG, and indicate that these hosts may offer improvements to Tm3+:YAG in increasing tunability in the 2 μm region and in improving laser performance for the 2.3 μm transition. Preliminary laser results of a Tm:CaYSOAP laser are also presented.

Single crystals of Nd(3+):SrGdGa3O7 (SGGM) have been grown and characterized as candidate crystals for improved diode pumped lasers. The width of the 809 nm absorption in this disordered oxide crystal is 8 nm FWHM. The fluorescence lifetime of the 4F3/2 - 4I11/2 transition at 1.06 micron is 245 microsec. Dopant levels of 4 percent Nd have been achieved while maintaining high optical quality material.

Grinding, lapping, and polishing are finishing processes used to achieve critical surface parameters in a variety of precision optical and electronic components. As these processes remove material from the surface through mechanical and chemical interactions, they may induce a damaged layer of cracks, voids, and stressed material below the surface. This subsurface damage (SSD) can degrade the performance of a final product by creating optical aberrations due to diffraction, premature failure in oscillating components, and a reduction in the laser induced damage threshold of high energy optics. As these defects lie beneath the surface, they are difficult to detect, and while many methods are available to detect SSD, they can have notable limitations regarding sample size and type, preparation time, or can be destructive in nature. The authors tested a nondestructive method for assessing SSD that consisted of tagging the abrasive slurries used in lapping and polishing with quantum dots (nano-sized fluorescent particles). Subsequent detection of fluorescence on the processed surface is hypothesized to indicate SSD. Quantum dots that were introduced to glass surfaces during the lapping process were retained through subsequent polishing and cleaning processes. The quantum dots were successfully imaged by both wide field and confocal fluorescence microscopy techniques. The detected fluorescence highlighted features that were not observable with optical or interferometric microscopy. Atomic force microscopy and additional confocal microscope analysis indicate that the dots are firmly embedded in the surface but do not appear to travel deep into fractures beneath the surface. Etching of the samples exhibiting fluorescence confirmed that SSD existed. SSD-free samples exposed to quantum dots did not retain the dots in their surfaces, even when polished in the presence of quantum dots.

We have spectroscopically evaluated crystals of Nd3+:SrGdGa3O7(Nd3+:SGGM) to assess their potential for use as diode pumped solid-state laser materials. The single crystals were grown by the Czochralski method, and the samples were oriented using x-ray diffraction. The host, SrGdGa3O7 is a uniaxial crystal with tetragonal symmetry and is a subset of the melilite series of minerals. The samples studied here were doped with 2 at. % Nd3+ in the melt with respect to the Gd ion. Polarized absorption spectra reveal that the absorption coefficient for light having its E vector perpendicular to the c-axis, Eσ is larger than that for E parallel, Eπ. The absorption coefficient for Eσ at 809 nm is 6.6 cm-1, more than two times larger than that for Eπ at the same wavelength. Similar differences in transition strengths have been measured in the emission spectra. Significant inhomogeneous broadening occurs in Nd:SGGM; the absorption linewidth at 809 nm is 10 nm FWHM. For a diode pumped solid-state laser this represents a significant improvement over the 1-nm FWHM linewidth in Nd: YAG at 810 nm. The fluorescence lifetime for the 4F3/2 → 4I11/2 transition at 1.06 µm is 245 µm in our Nd:SGGM crystals, which is 40% longer than lifetimes measured previously for Nd:SGGM crystals grown by the laser heated pedestal growth method,1 and is comparable to the 230-µm lifetime for Nd:YAG.

Continuous-wave laser emission at 1.94 μm is reported in Tm:CaY4(SiO4)3O at room temperature with Ti:sapphire laser pumping at 790 nm. Pump thresholds of 100 mW and slope efficiencies of 32% have been achieved. The 3H6–3H4 pump absorption peak of 6% Tm:CaY4(SiO4)3O is six times stronger than the 3H6–3H4 pump absorption peak of 6% Tm:YAG.