High average and high peak brightness slab laser

A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M²=1.5. Both an average brightness of 7×10⁹ W/cm²·sr and a peak brightness of 1×10¹⁵ W/cm2·sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of ~1 kW can be obtained at ~1 kHz with a higher average brightness of ~3×10¹⁰ W/cm²·sr and a higher peak brightness of ~3×10¹⁵ W/cm²·sr     

Diode-laser-based absorption spectroscopy diagnostics of a jet-typeO2(1Δ) generator for chemical oxygen-iodinelasers

Using diode-laser-based diagnostics, O₂(¹Δ) yield and water vapor fraction were measured at the exit of a jet-type singlet oxygen generator (JSOG) for a chemical oxygen-iodine laser (COIL). Chlorine utilization and gas temperature at the generator exit were also measured, simultaneously. For conditions corresponding to the maximum chemical efficiency of the supersonic COIL energized by the JSOG, the O₂(¹Δ) yield, water vapor fraction, chlorine utilization, and temperature at the generator exit are 0.65, 0.08 and 0.92, and 30°C, respectively. Increase of the basic hydrogen peroxide temperature results in an increase of the water vapor fraction caused by an increase of the saturated water vapor pressure in the generator. As the pressure in the generator rises from 18 to 60 torr, the yield decreases from 0.65 to O.48. Dependence of the yield on the generator pressure is consistent with a rate constant for the O₂ (¹Δ) energy pooling reaction of 2.7×10^-17 cm³·S^-1. The same rate constant explains the measured variation of the temperature along the flow in the diagnostic cell     

小型化轴流式非链式脉冲氟化氘激光器

采用轴流循环流动方式更新非链式脉冲氟化氘（DF）激光器工作介质，搭建了一台小型化自引发放电DF激光器实验装置，开展了轴流DF激光器输出性能实验研究。单脉冲工作时，在工作气体配比SF₆∶D₂=10∶1，总气压8 kPa时，实现单脉冲能量800 mJ激光输出，全波半高宽约120 ns，其性能与横流放电非链式脉冲DF激光器相似。重复频率放电时，实现了DF激光器重复频率20 Hz稳定运转，得到的最大输出功率为13.1 W，重频脉冲幅值差优于±5%，并展望了轴流式DF激光器高重频工作的前景。文中提出的轴流式非链式脉冲DF激光器为小型化、工程化中红外光源提供了新的技术途径。     

4H-SiC avalanche photodiode with multistep junction extensiontermination

4H-SiC avalanche photodiodes (APDs) are fabricated with a multistep junction termination extension. The leakage current density has been dramatically reduced to as low as 1 μA/cm² and photo-responsivity up to 10⁵ A/W has been achieved. The 4H-SiC APDs can run very stably at power densities up to 10⁴ W/cm²     

Experimental study of gain and output coupling characteristics of aCW chemical oxygen-iodine laser

Gain and output coupling characteristics of the CW chemical oxygen-iodine laser (COIL) are determined experimentally by means of varying the output coupling method. Under the conditions that the Cl₂ flow rate is 11.8 mmol/s, the I₂ molar flow rate is from 20 to 50 μmol/s, and the duct pressure is 200 Pa, the following were obtained from the experimental data: maximum values of output power of 58 W, and optimal output coupling factor of 1.50%, a resonator efficiency of 4.8%, an unsaturated small-signal gain of 1.55×10^-3 cm^-1, a threshold small-signal gain of 1.31×10^-3 cm^-1, a saturation intensity of 1150 W/cm², intraresonator losses of 9%, and an atomic iodine concentration of 2.85×10¹⁴ cm^-3. A comparison of these results to the published data of other COIL systems is presented     

Gain characteristics of an atmospheric sealed CW CO2laser

Experimental and analytical investigations have been made on unsaturated gain g0of a CO2electric-discharge convection laser, in which discharge current flow, gas flow, and the optical axis are mutually perpendicular. Stable glow discharges in sealed gas mixtures of CO2, CO, N2, and He were maintained at pressures up to 780 torr with an input power density of about 90 W/cm³. The ratio of electric field to neutral particle densityE/Nwas1.7 times 10^{-16}V . cm²and was independent of the total gas pressureP. The electron density in a positive column of the glow discharge was about4 times 10^{10}cm^-3. Detailed spatial distributions of g0at a wavelength near 10.6 μm were measured in the pressure range from 100 to 780 torr. Measurements were also made on the current dependence of g0and on the change in gowith discharge time. The g0distributions along the gas flow direction were found to agree with those calculated from the electron density distribution and the relaxation rate constant of the upper laser level on the basis of continuity equations for a two-level model. The integrated value of g0along the flow direction was proportional to P^-0.8whenE/N, electron density, and gas temperature were held constant. A maximum value of the g0distribution, which was proportional to P^-0.3, was 0.14 percent/cm at 780 torr.     

Fast axial flow CO2 laser excited by silent discharge

A fast axial flow CO₂ laser excited by silent discharge has been developed. With a new electrode system applied to the laser, homogeneous discharge of power density of up to 80 W/cm³ is obtained without applying any stabilization techniques on the discharge. An output laser power of 920 W in stable TEM₀₀ mode operation is attained with an efficiency of over 14%. Beam fluctuation common to fast axial flow lasers is suppressed by the combination of smooth gas flow and low CO₂ molar fraction     

2-kHz repetition rate XeF laser

High-repetition-rate laser action, up to 2 kHz, has been demonstrated in XeF molecules at 351 and 353 nm by using a blowdown fast transverse-flow system and a four-circuit, thyratron-switched, low inductance pulse generator. For a typical run, the transverse flow was uniform, and the average flow velocity was 25 m/s across a discharge region of1.4 times 0.4 times 30cm³. The gas mixture used was He:Xe:NF3= 100:1.5:0.5, and the total pressure was varied from 600-1200 torr. For single-pulse operation, the maximum laser output energy was 22 mJ/pulse, and the electric efficiency was 0.4 percent. For a 2-kHz repetition rate, the average laser output energy was approximately 12 mJ/pulse with 50 percent variations. Hence, an average output power of 24 W was obtained.     

Influence of the active zone diameter, on the UV-ion Ne-CuBr laserperformance

An active-zone-diameter scanning of an ultraviolet (UV) Cu⁺ laser excited in a nanosecond, pulsed longitudinal Ne-CuBr discharge with an excitation pulse repetition frequency of 19.5-25 kHz is carried out. The discharge conditions for achieving a maximum average output power on the UV lines-248.6, 252.9, 260.0, and 270.3 nm are found for each active zone diameter. A record average output power of 1.3 W is obtained for multiline operation. The specific average output power is 57 mW/cm³ at an active volume of 23 cm³. The highest peak pulse power and average laser power on the 248.6-nm laser line for the UV Cu⁺ lasers are also measured-3.25 and 0.85 W, respectively. A simplified kinetic model, which describes the discharge afterglow processes, is made     

A CuBr laser with 1.4 W/cm3 average output power

An average laser power of 6.7 W has been obtained from a small-bore CuBr laser with a constructive active volume of 4.77 cm³ , i.e., a record specific average power of 1.4 W/cm³ for multikilohertz operation of copper vapor lasers has been achieved. It was found that the small-bore CuBr laser can operate with a neon buffer at atmospheric pressures     

Effects of near-infrared laser and superluminous diode irradiationon Escherichia coli division rate

An investigation is conducted of the effect of a 1300-nm continuous-wave (CW) laser diode 950-nm modulated superluminous diode which had a fixed average power density of 1.2×10³ W/m ² at all variable repetition rates of 2, 26, 700, 1000, and 5000 Hz and had an equivalent pulse duration of 410, 31.1, 1.15, 0.82, and 0.16 ms, respectively. The effect of both diodes on the rate of Escherichia coli WP2 division was examined. It was found that the radiation of the CW mode of the 1300-nm laser diode increased the division of E. coli in the dose range of 0.9-9.0 J/cm². The 950-nm pulsed irradiation increased or inhibited the division rate of bacteria depending on the pulsing frequency and/or pulse duration     

Pulse energy scaling characteristics of longitudinally excited Sr+discharge recombination lasers

Pulse energy scaling of longitudinally excited Sr⁺discharge recombination lasers has been investigated for a series of tubes with active volumes of 30, 200, and 1000 cm³operating at low pulse repetition rates. Specific energy densities (sim 6-9 muJ/cm³in the short-pulse mode) and conversion efficiencies (∼ 0.1 percent) were found to remain approximately constant with increasing volume. Single pulse energies exceeding 6 mJ at λ 430.5 nm corresponding to peak powers aver 20 kW have been achieved.     

Reliability of ultra thin ZrO2 films on strained-Si

Ultra thin high-k zirconium oxide (equivalent oxide thickness 1.57 nm) films have been deposited on strained-Si/relaxed-Si_0.8Ge_0.2 heterolayers using zirconium tetra-tert-butoxide (ZTB) as an organometallic source at low temperature (<200 °C) by plasma enhanced chemical vapour deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. The trapping/detrapping behavior of charge carriers in ultra thin ZrO₂ gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Stress induced leakage current (SILC) through ZrO₂ is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of ZrO₂ layer. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of 10⁻¹⁹ cm² as compared to 10⁻¹⁶ cm² in SiO₂ has been observed. The trapping charge density, Q_ot and charge centroid, X_t are also empirically modeled. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating layer. Dielectric breakdown and reliability of the dielectric films have been studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t_bd > 1500 s) is observed under high constant voltage stress.     

A high-performance polysilicon thin-film transistor using XeClexcimer laser crystallization of pre-patterned amorphous Si films

A high-performance polysilicon thin-film transistor (TFT) fabricated using XeCl excimer laser crystallization of pre-patterned amorphous Si films is presented. The enhanced TFT performance over previous reported results is attributed to pre-patterning before laser crystallization leading to enhanced lateral grain growth. Device performance has been systematically investigated as a function of the laser energy density, the repetition rate, and the number of laser shots. Under the optimal laser energy density, poly-Si TFT's fabricated using a simple low- temperature (⩽600°C) process have field-effect mobilities of 91 cm²/V·s (electrons) and 55 cm²/V·s (holes), and ON/OFF current ratios over 10 ⁷ at V_Ds=10 V. The excellent overall TFT performance is achieved without substrate heating during laser crystallization and without hydrogenation. The results also show that poly-Si TFT performance is not sensitive to the laser repetition rate and the number of laser shots above 10     

Enhancing the Near-Infrared Spectral Response of Silicon Optoelectronic Devices via Up-Conversion

A silicon-based optoelectronic device that exhibits an enhanced response to subbandgap light is described. The device structure consists of a bifacial silicon solar cell with an up- converting (UC) layer attached to the rear. Erbium-doped sodium yttrium fluoride (NaY_0.8F₄ : Er_0.2 ³⁺) phosphors are the optically active centers responsible for the UC luminescence. The unoptimized device is demonstrated to respond effectively to wavelengths (lambda) in the range of 1480-1580 nm with an external quantum efficiency (EQE) of 3.4% occurring at 1523 nm at an illumination intensity of 2.4 W/cm² (EQE = 1.4 times 10^-2 cm²/W). An analysis of the optical losses reveals that the luminescence quantum efficiency (LQE) of the device is 16.7% at 2.4 W/cm² of 1523-nm excitation (LQE = 7.0 times 10^-2 cm²/W), while further potential device improvements indicate that an EQE of 14.0% (5.8 times 10^-2 cm²/W) could be realistically achieved.     

Study of etch rate characteristics of SF6/He plasmas byresponse-surface methodology: effects of interelectrode spacing

The characteristics of SF₆/He plasmas which are used to etch Si₃N₄ have been examined with experimental design and modeled empirically by response-surface methodology using a Lam Research Autoetch 480 single-wafer system. The effects of variations of process gas flow rate (20-380 sccm), reactor pressure (300-900 mtorr). RF power (50-450 W at 13.56 MHz), and interelectrode spacing (8-25 mm) on the etch rates of LPCVD (low-pressure chemical vapor deposition) Si₃N₄, thermal SiO₂, and photoresist were examined at 22±2°C. Whereas the etch rate of photoresist increases with interelectrode spacing between 8 and 19 mm and then declines between 19 and 25 mm, the etch rate of Si₃N ₄ increases smoothly from 8 to 25 mm, while the etch rate of thermal SiO₂ shows no dependence on spacing between 8 and 25 mm. The etch rates of all three films decrease with increasing reactor pressure. Contour plots of the response surfaces for etch rate and etch uniformity of Si₃N₄ as a function of spacing and flow rate at constant RF power (250 W) display complex behavior at fixed reactor pressures. A satisfactory balance of etch rate and etch uniformity for Si₃N₄ is predicted at low reactor pressure (~300 mtorr), large electrode spacing (12-25 mm), and moderate process gas flow rates (20-250 sccm)     

Noncontact high-speed waveform measurements with the picosecondphotoelectron scanning electron microscope

The authors have replaced the electron gun and beam blanking system of a conventional voltage contrast scanning electron microscope by a pulse-laser/photocathode combination, resulting in a source producing electron pulses of order 1 ps in duration at a 100 MHz repetition rate and with a peak brightness of 3 10⁸ A/cm² sr at 1.8 keV. This novel instrument has demonstrated stroboscopic noncontact waveform measurements on metal interconnect lines in different environments with a temporal resolution between than 5 ps, a voltage resolution of 3 mV/(Hz)^1/2, and a spatial resolution of 0.1 μm. These measurements are achieved with extraction fields above the sample of about 1 kV/mm     

RF excitation of a flowing gas CO2 waveguide laser

Investigation of an RF excited CO₂ waveguide laser in flowing gas operation is reported. Power extraction of 0.8 W/cm with an efficiency of 10.3% has been achieved. Using W.W. Rigrod's analysis (1965), values of the small-signal gain α₀ and saturation parameter I_s have been determined for different excitation levels and for different pressures of the amplifying medium. The parameters α₀ and I_s, have been determined as 0.6%/cm and 10.4 kW/cm ², respectively, at 125 torr and 100 W/cm³ RF loading power. These values are close to those reported for sealed-off RF CO₂ waveguide lasers with xenon added to the gas mixture     

Repetitively pulsed, 70-J photolytic iodine laser with excellentoptical and long/reliable operation

The performance of a repetitively pulsed, 70 joule, closed cycle 1.3 μM photolytic atomic iodine laser with excellent beam quality (BQ=1.15) is presented. This BQ was exhibited in the fundamental mode from a M=3.1 confocal unstable resonator at a 0.5 Hz repetition rate. A closed cycle scrubber/laser fuel system consisting of a condensative-evaporative section, two Cu wool I₂ reactor regions, and an internal turbo-blower enabled the laser to operate very reliably with low maintenance. The fuel system provided C₃F ₇I gas at 10-60 torr absent of the photolytic quenching by-product I₂. Using a turbo-molecular blower longitudinal flow velocities greater than 10 m/s were achieved through the 150 cm long by 7.5×7.5 cm² cross sectional photolytic iodine gain region. In addition to the high laser output and excellent BQ, the resulting 8-12 μs laser pulse had a coherence length greater than 45 meters and polarization extinction ratio better than 100:1. Projections from this pulsed photolytic atomic iodine laser technology to larger energies, higher repetition rates, and variable pulse widths are discussed     

CuInSe2 cells and modules

Recent CuInSe₂ photovoltaic technology advances are discussed. 14.1% active area efficient test cells and the fabrication of monolithic integrated modules with power outputs of 112 W/m² on 940 cm² and 91.4 W/m² on 3900 cm² have been achieved. Packaged modules are stable outdoors. Studies indicate a recombination controlled junction mechanism and imply a wide CIS compositional range over which high-efficiency junctions are possible. Processing improvements already demonstrated on test cells and 940 cm² modules will yield 52-W, 3900-cm² CIS modules