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This communication describes a new method for producing stable, high concentrations of Sc2+ in optically clear CaF2 crystals. We have achieved Sc2+ concentrations as high as 3 × 1018 cm−3 without degradation of optical quality. We have converted as much as 5% of the scandium dopant to the divalent state. The concentration of divalent scandium is stable during room temperature storage for periods of at least one year.

The 2-μm pumped AgGaSe2 OPO is currently limited to outputs below 1 W and pulse recognition frequencies of a few kilohertz, apparently because of thermal lensing. Conflicting values for K and dn/dT and the lack of accurate 2-μm absorption data have severely hampered predictions of thermal focusing from material properties. We present results of polarized 2-μm laser calorimetry and extracavity thermal lens measurements on AgGaSe2 samples grown at two laboratories over the past 5 years. We show that the 2-μm absorption is due primarily to an e-polarized extrinsic band. Even for our best material, the thermal focal length can be comparable to the crystal length (in a typical OPO configuration) at pump powers of only a few watts. We find no astigmatism due to crystalline anisotropy, and we demonstrate the possibility of intracavity optical compensation. We have also achieved an order of magnitude reduction in thermal focusing by cooling the crystal to 77 K.

Blue and UV fluorescence bands have been observed in Cr:Tm garnet laser materials under cw excitation at 632.8 nm. Previous studies have attributed this anti-Stokes fluorescence to upconversion processes involving Cr-Tm energy transfer. These studies have also suggested that this Cr-Tm upconversion substantially limits the efficiency of flashlamp-pumped Cr:Tm-sensitized 2-μm lasers.1 In the present investigation, by using a cw dye laser tuned over the 610-680 nm range, we have measured relative intensities of emission bands and the corresponding excitation spectra in garnets doped with Tm:Cr and with Tm alone. The results clearly demonstrate that the principal source of the blue and UV fluorescence is not upconversion but is excited-state absorption of Tm3+, which takes place in the 3F4 → 1G4 level and the 3H4 → 1D2 levels, respectively. The blue fluorescence, which peaks at approximately 480 nm, arises through emission from the 1G4 level to the 3H6 ground state of Tm3+, and the UV fluorescence, peaked near 360 nm, is due to the 1D2 → 3H6 transition. The results indicate that these processes have negligible effects on the efficiency of Cr:Tm-sensitized 2-μm lasers.

The darkening and subsequent fading of silver‐halide photochromic glass upon irradiation with a Q‐switched laser pulse has been investigated. Together with new steady‐state optical measurements and ESR observations of photolytic Cu++, the data reveal three major components of the darkening at room temperature: prompt (τ

Electron spin resonance and etch-back techniques have been employed to identify radiation-induced defect centers in thermally grown oxide films on SOS wafers and to determine their spatial distribution in the oxide film. The only defect identified was the E' center, which was found to be indistinguishable from E' centers in irradiated bulk fused silica samples. The distribution of E' centers in-oxide films irradiated to a dose of 108 rad (Si) was observed to consist of a uniform bulk distribution plus a concentration build-up near the Si-SiO2 interface. The application of a positive 10 volt bias to a 1.08kA gate oxide during gamma irradiation produced an order of magnitude increase in the E' center concentration.

Magnetic hysteresis effects have been observed in ferromagnetic resonance (FMR) spectra obtained at 9 and 16 GHz for certain simulated lunar glasses which were reduced by H 2 in the melt and rapidly quenched. Transmission electron microscopy has revealed that these samples contained spherical particles in the size range ∼0.01–0.5 μm. FMR spectra obtained at 35 GHz (applied field ∼ 12.5 kOe) exhibited a line shape characteristic of spherical, single-domain (SD) iron particles with no hysteresis. Computer simulations of the latter spectra confirmed that the average deviation from sphericity must be ≲3% and that (2 K 1 / M s ) ≈ + 600 Oe for the precipitated magnetic phases. The principal features of the spectra obtained at all three frequencies have been explained on the basis of a simple theoretical treatment for spherical iron particles which have 2 domains in applied fields ≲7 kOe, but become saturated at higher fields. Isothermal remanent magnetization (IRM) of these samples has been studied by both FMR and standard static techniques; the mean coercive force measured by the former (∼4 kOe) contrasts with the mean value determined by the latter (∼550 Oe). Apparently, FMR singles out and even amplifies the contributions of two-domain particles (which are magnetically hard), while the static measurement is more sensitive to the average of all particles present. The intensity of the FMR hysteresis of typical lunar soils is found to be ∼1% of the total FMR intensity. In spite of this seemingly small value, two-domain iron particles may be important carriers of natural remanent magnetization (NMR) in certain lunar rocks.

We have investigated laser‐assisted reactions in Hg/HgBr2 gas mixtures by measuring fluorescence from the product, HgBr radical, following simultaneous IR (1064 nm) and UV (253.7 nm) laser excitation. The product emission has one‐photon dependence on both IR and UV laser power, and the results indicate that the excited HgBr product channel is accessed through single photon absorptions by the {Hg–HgBr2} complex. This constitutes the first experimental evidence for an electronically excited state of the {Hg–HgBr2} collision complex, having an energy level >4.9 eV but

Measurements of optical absorption, kinetics, electron‐spin resonance, and flash photolysis, as well as x‐ray fluorescence and wet‐chemical analysis, have been applied to a series of silver‐halide photochromic glasses having precisely controlled variations in silver and copper concentrations as well as in the size of the precipitated silver‐halide microphases. These combined experimental data have enabled us to clarify the manner in which copper enters the microphases and the mechanisms whereby it affects their photochromic properties. Most notably, we have succeeded in determining the site and valence‐state distribution of copper ions, produced by the separation of the microphases. We have demonstrated, for example, that copper enters the silver‐halide phase only as cuprous ions, which then act as the dominant hole traps in the photochromic darkening process. Optical absorption of these cuprous ions in the silver‐halide phase was also found to make a major contribution to the absorption edge observed in the undarkened photochromic glasses. The increase of thermal fade rate with increasing copper content is discussed in light of these new experimental results.

Optical and TEM measurements are reported on a series of well‐characterized photochromic glasses containing silver‐halide microparticles. The growth rate for formation of photolytic silver is found to vary inversely as some fractional power of the silver‐halide particle diameter. Comparison with simple models suggests that in these experiments silver cluster growth is being limited by the motion of surface ions. This type of experiment may provide a model system for studying the mechanism of photographic latent‐image formation.

Microwave resonance thermomagnetic analysis (MRTA) is the name given to a newly evolved technique for inferring the natures of fine-grained ferromagnetic constituents in lunar materials. Based on standard ferromagnetic resonance (FMR) procedures, the method makes use of the microwave skin effect for diagnosing the presence of metallic iron. Modelling experiments carried out on well-characterized iron and magnetitelike precipitates produced independently in simulated lunar glasses, coupled with published data for magnetite, provide a potential basis for detecting and discriminating between iron metal and ferric iron spinel, even when both are present in an unknown sample. Application of the technique to the lunar samples indicates the possible existence of magnetitelike phases in amounts up to about 0.3 wt% in soils from seven samples regions of the moon. These findings do not require any special geologic processes for their explanation, although some evidence supports the suggestion that fumarolic activity may have occurred in the lunar highlands.

Optical absorption and diffuse reflectance spectra were obtained for simulated lunar glasses of four different compositions, both in their as-quenched (reduced) states and following mild subsolidus oxidation. The transmission spectra, when normalized by the FeO content of the glasses, differed from one another only in the relative intensity of an unresolved band in the UV. For fixed melting conditions the strength of this band in the as-quenched glasses increased with increasing FeO, or with increasing TiO2 for a fixed FeO content. Electron spin resonance (ESR) experiments have demonstrated the absence of Fe3+ or Ti3+ and the presence of metallic iron in these materials; all other transition-group elements were excluded in preparation. The unresolved UV absorption edge in the as-quenched reduced glasses is therefore tentatively ascribed to Fe2+→Ti4+ intervalency charge transfer transitions. A similar UV edge was also produced by oxidation, leading to the conclusion that the assignment of this band would be ambiguous in the absence of an independent determination of the valence states of Fe and Ti. The relationship between the transmission spectra of polished samples and the reflectance spectra of sieved powders of the same materials is shown to be well described by the Kubelka-Munk approximation. Using this insight, it is possible to understand the spectral characteristics both of oxidation darkening of synthetic glass powders and of maturation darkening of lunar soils in terms of (1) the growth of the aforementioned charge transfer band(s) and (2) the development of opaque surface phases. It is shown that mechanism (1) is of primary importance in lunar highland materials and that mechanism (2) dominates in mare materials. The present results, coupled with previous findings, suggest that lunar soil maturation darkening may result from vitrification only if accompanied by (a) enrichment in the elements Fe and Ti, (b) changes in valence states of these elements, (c) partial crystallization of opaque phases such as iron, ilmenite or magnetite, or (d) a combination of (a), (b), and (c).

Current‐voltage behavior of the dark current and photocurrent, photocurrent frequency response, and light spot profiles have been measured for silicon phototransistors irradiated by short pulses from a neodymium glass laser above energy densities of 10 J/cm2. The principal bulk damage effects observed were the generation of an Ohmic dark current, the formation of localized conduction paths, and the narrowing of the base layer of the device. An empirical model was used to account for these results and was shown to be consistent with previous predictions based upon the migration of phosphorus across the detector by laser‐induced melting and subsequent refreezing.

Redistribution of phosphorus dopant in 1N2175 phototransistors damaged by a pulsed neodynium laser has been investigated using the electron microprobe technique. Four different effects observed in the concentration profdes were explained by the action of diffusion and segregation, in the presence of temperature and compositional gradients. One specific effect was analyzed using a simplified model consisting of diffusion in the melt followed by the segregation upon refreezing. It was estimated that certain areas of the phototransistor surface remained above the melting point for times of the order of 10−4 sec. Correlation was made between the results of these microprobe measurements and previously observed laser-damage effects in the electrical characteristics. It is suggested that impurity migration may be an important mechanism for damage to junction devices by pulsed lasers in an intermediate energy range.

An LCAO–MO energy level diagram and bond length estimates are used to describe a planar ethylenic molecule model for the N2H4+ defect at an NH4+ site in ammonium halides. The unpaired spin orbital is found to be an antibonding combination of 2p orbitals on each nitrogen perpendicular to the molecular plane. The model is then further specified and used to analyze the low‐temperature EPR data for NH4Cl in detail, from which hyperfine, bond length, and bond angle parameters are extracted and compared with LCAO–MO calculations. Thereby, more information about the defect and confirmation of the model are obtained. Satellite intensity and linewidth angular variations in the high‐temperature spectra are explained, and the relation of high‐ to low‐temperature spectra is discussed.

We have measured first Stokes conversion efficiency as a function of pump power for stimulated Raman scattering in liquid nitrogen at pump wavelengths of 0.532, 1.06 and 21.05 μm. An anomalously large Raman susceptibility was observed in the case of 2.05→3.92 μm conversion. The mechanism of this effect is tentatively identified as a preresonance enhancement of the Raman cross‐section in the vincinity of a collision‐induced absorption band associated with the first vibrational overtone of nitrogen.

Ferromagnetic resonance studies were carried out at 9, 16, and 35 GHz on spherical particles of metallic iron ∠0.01‐0.5 μm precipitated in an Fe2+‐containing silicate glass by hydrogen reduction. The 35 GHz spectrum was successfully computer simulated under the assumption that magnetocrystalline anisotropy was predominantly responsible for the powder line shape, leading to the conclusions that 2K1/Ms?+600 Oe for the precipitated particles and that the mean deviation from sphericity was ≲4%. In contrast, at the lower frequencies the spectra were characterized by (1) a continuous absorption extending from zero field to a mean‐cutoff of ∠7 kOe and (2) a hysteretic component appearing ∠ 2.5 kOe below the free electron resonance field as a results of isothermal cycling to ≳4 kOe in situ. The position of the latter feature is in good agreement with a theoretical calculation of the resonance fields of a two‐domain sphere of iron with a thin domain wall. The results support the predictions of Amar1 that magnetiza...

The ferromagnetic phases which precipitate from various iron‐containing silicate glasses have been identified and characterized by studying the integrated intensity of the ferromagnetic resonance absorption as a function of sample temperature between 4.2 and 570°K. The analysis makes use of the effect of microwave skin depth on the FMR intensity to estimate the average particle size for fine disperisions of metallic iron, and experimental results on well‐characterized glasses are in good qualitative agreement with theory. Furthermore, by using the results of modelling experiments carried out on iron and magnetitie precipitates produced independently in different glasses, it is possible to detect and discriminate between metallic iron and ferric iron spinel, even when both are co‐present in an unknown sample. This result is important because spectra characterized by positive magnetocrystalline anisotropy constants have been observed in samples containing fine†grained magnetite.

IR excitation of selected vibrational modes of a variety of molecules trapped in solid rare gases causes a photoisomerization. The reactions are generally single photon processes which involve a rotation about a single bond. The quantum yields for photoisomerization have now been measured in both the forward and re verse directions for several molecules. The range of excitation includes both the fundamental and first overtone vibrations. These quantum yields vary from 0 to 1. The vibrational photochemistry is not consistent with a statistical redistribution of energy in the guest molecule before reaction. The guest molecules are not isolated in a gas phase sense; vibrational energy flow to the lattice competes with reaction and intramolecular (guest) energy redistribution. It is likely that relaxation of the guests can occur via specific pathways. Evidence is presented to show that the products and the quantum yields for their formation depend on the relaxation rates and pathways. It is thus possible to create product distributions by even broadband (nonlaser) IR irradiation that are impossible thermally.

Since the return of the first lunar samples by the Apollo 11 astronauts, lunar material has been investigated by virtually every well-known chemical, physical, and mineralogical technique.1 It is known, for instance, that lunar soils comprise up to 50% glass and that these lunar glasses have compositions similar to those of the “moon rocks”, i.e., 40–50% SiO2, 30–40% (CaO+MgO+FeO), 10–20% Al203, 0–8% TiO2 and