Laser actinometry of flash-photolyzed H2/F2/He mixtures

Actinometric and time-to-threshold experiments with flash-initiated H2/F2/He mixtures have been modeled with the RESALE chemical laser code. Comparison of the salient features of both experiments with those predicted by the code determines the efficiency of our xenon flashlamp in dissociating F2. The results indicate that our 1000-J 20-μs full width at half maximum (FWHM) lamp is capable of dissociating 1.2 percent of the F2initially present in dilute F2/He mixtures.     

The photoionization cross sections of the Rg*2[3Σ+u] excimer states for Ne*2, Ar*2, and Kr*2

Based on the recently determined Rydberg series of the³Sigma+_{u}excimer states of Ne*2, Ar*2and Kr*2, the photoionization cross sections of these molecules are calculated using a single-channel quantum defect method. These cross sections are found to differ considerably from those of the asymptotic metastable atomic Rg*(ns^{3}P_{2}) states, but are in good agreement with recently reported experiments at isolated wavelengths. The implications of these results for VUV and XUV lasers are discussed.     

Accurate gas diagnostics for sealed-off CO2 lasers usingnear-infrared DFB semiconductor lasers

The selective spectroscopic detection of CO₂ and H₂O in the gas mixture of a 400-W sealed-off CO₂ slab laser is reported. The detection is based on the acquisition of absorption Voigt profiles of two vibrational overtone transitions of CO ₂ and H₂O, obtained using two InGaAsP distributed feedback (DFB) semiconductor lasers. This spectroscopic method enables a direct absolute measurement of the temporal evolution for the concentrations inside the laser active volume. Monitoring takes place during laser operation without gas extraction. The experiments carried out on CO₂ and H₂O abundances confirm the paramount importance of wall desorbance phenomena in all-metal radio frequency (RF) excited lasers     

Linear and nonlinear optical properties of AgGaS2, CuGaS2, and CuInS2, and theory of the wedge technique for the measurement of nonlinear coefficients

The refractive indices of the ternaryA^{I}B^{III}C_{2}^{VI}semiconductors AgGaS2, CuGaS2, and CuInS2have been measured over the entire range of transparency of these crystals. The optical nonlinear coefficients for second-harmonic generation have also been determined. Three-frequency collinear phase matching is analyzed in detail for AgGaS2. The birefringences of CuGaS2and CuInS2are not large enough to permit three-frequency phase matching within the transparent regions. A parametric oscillator threshold calculation for a pump wavelength 0.89 μ, which is within the range of the GaAs injection laser, indicates that AgGaS2is promising for this application. The upconversion efficiency in AgGaS2for sum mixing of the CO2laser (lambda = 10.5 mu) with the xenon ion laser (lambda = 0.597 mu) is also calculated. The result indicates that, depending upon system requirements and the availability of high optical quality material, AgGaS2can be comparable to ZnGeP2for upconversion. In Appendix II, we present a theory of the wedge technique for the measurement of nonlinear coefficients. This theory takes into account losses and assumes a Gaussian beam geometry. Furthermore, a discussion of units in nonlinear optics is given.     

Near single-line operation of a free-burning CS2/O2/N2O flame laser with a nondispersive optical cavity

The CS2/O2/N2O flame laser has been operated for the first time under conditions in which the spectral output is nearly single line. This transition is theP_{10-9}(17) of CO at 5.4265 μm, the same transition which was observed to oscillate in single-line fashion by Hirose et al. in an electrically initiated CO chemical laser. It is suggested that the unique behavior of this line may be due to its close proximity to aPbranch transition in an adjacent band, namely theP_{9-8}(23) line, such that the gain profiles of the two lines overlap. Calculations suggest that at the conditions of these experiments, the separation of the line centers for this pair is about 0.3 Å or less. TheP_{10-9}(17) transition was also found to be totally absent under certain conditions of high multiline power, particulary at low O2and N2O flows. This may be due to absorption by a high-bandRbranch transition at 5.4266 μm, namely theR_{15-16}(32) line.     

A laser augmented reaction: SF6+ SiH4→S*2+ SiF4+ HF + H2· retention of isotopic selectivity during detonation

A single unfocused pulse of a free running CO2laser, area ∼ 8 cm², initiates an explosive reaction between SF6and SiH4. This occurs at a minimum energy of 4 J [full width at half maximum (FWHM)sim 1.5 /mus] of which about one half is absorbed in an 8 cm long cell; total pressure 12 torr; 0.65 <p(SiH4)/p(SF6) < 1.8. The spectral and temporal distributions of the emitted chemiluminescence depend sensitively on the fuel to oxidizer ratio, and on the pulse energy; we investigated the range 4 → 20 J. The principal emission is due to S2(B^{3}Sigma-_{u} rightarrow X^{3}Sigma-_{g}). Transitionsupsilon' (0-4) rightarrow upsilon" (2-15)were recorded. In the³Sigma-_{u}state, vibrational temperatures range from 3000-13000 K. The luminosity peaks sharply at (SiH4)/(SF6) = 1.0 ± 0.05. On each side of the maximum of the emission versus composition curve [at (SiH4)/(SF6) ≈ 0.95 and 1.22, for a 12 J pulse] the residual SF6(0.2-0.5 percent of initial amount) is enriched in³⁴SF6; the observed fractionation factors at these two compositions are 8 ± 2. The separation between the two sharply peaked optimum compositions appears to increase with increasing pulse energy. Preliminary results with other fuels suggest that the concurrent absorption of CO2laser radiation by the fuel, as well as a highly exothermic reaction, are pre-requisite for fine tuning of composition, injected power, and total pressure for optimum isotope fractionation.     

Work function of WSi2

The work function of tungsten disilicide (WSi2) has been measured by MOS capacitance-voltage technique. MOS capacitors with WSi2as the gate material have been fabricated on n-type     

Characteristics of MOSFET prepared on Si/MgO.Al2O3/SiO2/Si structure

A new silicon on insulator (SOI) wafer with epitaxial-Si/ epitaxial-MgO.Al2O3(0.1 µm)/SiO2(0.5 µm)/     

Long-pulse N2UV lasers at 357.7, 380.5, and 405.9 nm in N2/Ar/Ne/He mixture

Using long-pulse electron-beam pumping, long-pulse laser emissions at 357.7, 380.5, and 405.9 nm have been observed in the second positive system of nitrogen with pulse durations of 150, 400, and 400 ns, respectively. Substantial improvements in laser performance were observed by adding excess Ne and He into N2+ Ar mixtures. Peak powers of 56, 44, and 66 kW/cm²have been obtained for the three wavelengths, respectively.     

F_2/H_2链反应脉冲化学激光器简化模型计算

列出了补偿Kerber简化模型缺陷的光引发F_2/H_2链反应脉冲激光器的简化模型。解决了振转跃迁光通量方程与动力学速率方程之间时间坐标的相容性问题。采用Gear自动积分法获得满意的数值计算结果。列出F_2/H_2预反应生成的HF(O)、混合物中O_2含量、光引发剂等对激光性能影响的定量结果。     

Composite TaSi2/n+poly-Si formation by rapid thermal annealing

Composite TaSi2/n+ poly-Si structures have been formed by rapid thermal annealing (RTA). Polysilicon films 0.2 µm thick were deposited on oxidized Si wafers by LPCVD and heavily doped with phosphorus by diffusion. A layer of TaSix0.22 µm thick was then cosputtered on polysilicon from separate targets. The as-deposited samples were annealed by RTA using high-intensity tungsten lamps. Uniform stoichiometric low-resistivity tantalum disilicide was formed by RTA in 1 s at 1000°C. The sheet resistance and grain size of the silicide layers are comparable to those formed by conventional furnace anneals. The surface morphology of the RTA samples is superior to that obtained by furnace annealing. These results show that RTA technique has a great potential for low-resistivity tantalum silicide formation in VLSI circuits.     

Nonlinear optical susceptibility of HgGa2S4

The second harmonic coefficient d36of HgGa2S4has been measured to be 5 times larger than d36(LiNbO3). The birefringence is usefully large.     

Two switching devices utilizing VO2

Vanadium dioxide undergoes a crystallographic phase transformation at 68°C which is accompanied by a large and abrupt change in resistivity. Two devices, a two-terminal threshold switch and a four-terminal thermal relay, based on this effect are investigated theoretically and experimentally with regard to switching applications. The formation of thermal filaments is found to have a strong influence on both the dc characteristics and on the switching properties. One consequence for both devices is that the power required to sustain the "on" condition is significantly less than that required for switching. It is shown that both devices should be capable of submicrosecond switching times at milliwatt power levels.     

Acoustooptic tunable filter using TeO2

A new type of acoustooptic tunable filter using noncollinear interaction in TeO2has been fabricated. Dynamic bandwidth of the filter is in the range between 0.42 and 0.75 µm and corresponding acoustic frequency is between 85 and 40 MHz. Efficiency up to 90 percent is obtained at the electrical power input of 50-400 mW and resolution of 12-25 Å is attained experimentally.     

Nonlinear optical susceptibility of the thiogallate CdGa2S4

The nonlinear optical coefficient d36of CdGa2S4was measured to be 5 times larger than d31(LiNbO3). This large non-linearity is in good agreement with theory.     

Linear dichroism in photochromic CaF2

Photochromic switching of additively colored La, Ce, Gd, or Tb doped CaF2with linearly polarized UV light and subsequent thermal decay of other photochromic effects leads to a linear dichroism of the two major absorption bands, band 1 (∼4000 Å) and band 2 (∼6000 Å), of the thermally stable state. The dichroism is due to a net reorientation of an anisotropic center having a symmetry axis that can lie along any one of the fourlangle111ranglecrystal directions. The photochromically active band, band 1, is shown to be due to an absorption dipole in the direction of the symmetry axis, while band 2 is due to two orthogonal absorption dipoles perpendicular to the symmetry axis. The direction of the symmetry axis and the character of the absorption bands suggest anFcenter perturbed by a rare earth replacing a nearest neighbor Ca. A possibility remains, however, that the center is more complex.     

Orientation and thickness dependence of contrast and brightness in Gd2(MoO4)3light valves

Bistable light valves comprising single crystal gadolinium molybdate have been proposed which utilize either the interchange of fast and slow directions in c-cut plates or the alteration of extinction directions in oblique sections upon ferroelectric switching. Several device configurations of each type are analyzed for brightness and contrast as functions of crystallographic orientation and thickness of the ferroelectric plate. The results facilitate quantitative comparisons among devices and predict the sacrifice in optical performance incurred when thickness is reduced to lower the drive voltage required for switching. For equivalent optical performance, the switching voltage should be 43 percent higher in valves of the extinction-direction type. The analysis predicts that no oblique section exists for which display brightness at maximum contrast is higher than that obtainable on a c-cut section of equal thickness.     

Refractory MoSi2and MoSi2/polysilicon bulk CMOS Circuits

Refractory MoSi2and MoSi2/polysilicon have been used to fabricate high-performance 3µm bulk CMOS circuits. Thirty-nine stage ring oscillators, with a fan-in and fan-out of 1, exhibit a switching delay/stage of 1.2 to 1.4ns, and a power-delay product of 0.22 to 0.25pJ at a supply voltage of 5V. The power-delay product ranges from 40fJ for a delay of 9ns to 1pJ for a delay of 0.6ns. Self-checking pattern generator circuits implemented with the same technology show an operating frequency as high as 80 MHz, which corresponds to approximate in-circuit delays of 1.2ns/stage.