Gain characteristics of an axial gas discharge interacting with atransverse rotating magnetic field

Gain measurements within an axial discharge interacting with a transverse rotating magnetic field are presented. The effects of applied voltage and magnetic field strength on centerline gain are discussed. This is followed by an investigation of the radial gain profile and the saturation intensity. Observed values of the small signal gain and the saturation intensity were 0.85 m^-1 and 160 W/cm², respectively     

Gain characteristics of a MAGPIE coaxial CO2laser system

Gain coefficient measurements of a MAGPIE (magnetically stabilized, photoinitiated, impulse-enhanced, electrically excited) coaxial CO2laser discharge are presented. The effects of gas composition, input power, pulser ionization, and magnetic field on gain are examined. Measurements of the radial gain profile and saturation intensity are also discussed. A maximum small-signal gain of 0.30 m^-1is observed, along with a saturation intensity of 190 W/cm².     

Measurement of carrier escape rates, exciton saturation intensity,and saturation density in electrically biased multiple-quantum-wellmodulators

In this paper, we detail the results of exciton saturation intensity measurements on strained InAsP/InP and InGaAs/GaAs multiple quantum well modulators designed for 1 μm operation and under electrical bias as is required for device operation. Carrier escape times from the quantum well were also measured for both electrons and holes. These measurements allow the first experimental determination of the saturation density of the material under electrical bias. This density can also be calculated using a theoretical model proposed by Schmitt-Rink, et al. The experimentally measured density is in good agreement with this theoretical model     

Spin saturation and pump depletion in continuous spin-flip Raman oscillation

A saturation model of stimulated Raman scattering, of general applicability, is put forward. The model is developed with reference to spin-flip electronic Raman scattering in InSb, where the number of excitations available for Raman scattering may be small by comparison with the incident photon numbers. A rate equation technique is used to evaluate the steady-state Stokes intensity and output powers for a Gaussian pump beam. The model is extended to take account of pump depletion and the relative importance of depletion, and saturation in limiting the conversion efficiency under different conditions is brought out. By comparison with continuous wave spin-flip measurements, values are obtained for the spin-relaxation time (τs) associated with spin reversal in InSb. For 10¹⁶free carriers per cubic centimeter at 36 kG,tau_{s} sim 12ns and for 10¹⁵cm^-3at 16.9 kG,tau_{s} sim 1.3ns.     

Velocity dependence of the gain of a CO2laser

Measurements of the small signal gain and saturation intensity of a CO2-N2-He laser are made as a function of gas flow velocity over the range fromsim 0-10m/s. The small signal gain increases and the saturation intensity decreases with increased gas velocity. For intermediate flow velocities with a gas transit time in the laser of a second, the gain also depends on the direction of propagation of the amplified beam with respect to the gas flow. The directional dependence is due to an axial gradient in the saturation intensity. The transit time of the gas in the 2.5-m amplifier spans the time required for appreciable generation of CO by dissociation of the CO2and the variation of the laser gain with velocity is attributed to the effects of CO on the inversion of the laser medium.     

Intersubband absorption saturation in InGaAs-AlAsSb quantum wells

We present intersubband absorption saturation studies in InGaAs-AlAsSb quantum wells. We carried out a density matrix calculation to simulate the pulsed excitation condition after including the dephasing time and the short pulse profile to estimate the saturation intensity (I/sub S/). We compare the calculated results with measurements for both resonant and nonresonant excitation. We also present our results on the effect of pulsewidth on Is estimation.     

Source, drain, and gate series resistances and electron saturation velocity in ion-implanted GaAs FET's

Techniques which allow us to determine the series source, drain, and gate resistances and the electron saturation velocity of ion-implanted GaAs FET's are described. These techniques are based on the "end" resistance measurements. The theory of this method is developed and used for a new interpretation of the "end" resistance measurements. The values of the series resistances determined by this technique are shown to be in an excellent agreement with those obtained by the modified Fukui method. The values of the electron saturation velocity varying from 1.0 × 10⁵m/s to 1.3 × 10⁵m/s are obtained using the end resistance method. The proposed set of measurements is simple and accurate enough to be used as a routine characterization technique for GaAs FET's.     

Gain and saturation intensity of the green Ho:ZBLAN upconversionfiber amplifier and laser

The gain and saturation intensity of the green Ho-doped fluorozirconate (ZBLAN) glass fiber amplifier and laser, pumped in the red (643 ⩽ λ_p ⩽ 649 nm; ⁵F₅ ← ⁵I₈), have been measured. For a 2.4-μm core diameter fiber 45 cm in length, the single-pass gain at 543.4 nm exceeds 12 dB for 90 mW of pump power at 643.5 nm. The saturation power for the ⁵F₄, ⁵S₂ → ⁵I₈ lasing transition was determined from gain measurements to be 970 ± 175 μW, which corresponds to a saturation intensity of 19.8 ± 3.5 kW · cm^-2 , and a stimulated emission cross section approximately one order of magnitude larger than theoretical estimates     

New technique for measurement of electron saturation velocity in GaAs MESFET's

A new technique for the measurement of the electron saturation velocity in GaAs FET's is proposed using the "end" resistance measurement. The measurements performed on 1.3-µm gate-length ion-implanted GaAs MESFET's lead to the values of the saturation velocity ranging from 1 to 1.3 × 10⁵m/s.     

连续激光辐照CMOS相机的像素翻转效应及机理

为了研究激光对CMOS图像传感器的干扰效果,利用632.8 nm连续激光开展了对CMOS相机的饱和干扰实验。随着入射激光功率的增加,分别观察到未饱和、饱和、全屏饱和等现象,并发现,在全屏饱和前,功率密度达到1.4 W/cm2后,光斑强区中心区域出现了像素翻转效应。进一步加大光敏面激光功率密度到95.1 W/cm2,激光作用停止后相机仍能正常成像,证明像素翻转效应并非源自硬损伤。基于CMOS相机芯片的结构和数据采集处理过程进行了机理分析,认为强光辐照产生的过量光生载流子使得光电二极管电容上原来充满的电荷被快速释放,使得相关双采样中的两次采样所得信号Vreset与Vsignal逐渐接近,是输出像素翻转的一种可能原因。     

Small-signal gain and saturation parameter of a transverse-flow CW oxygen-iodine laser

The small-signal gain and saturation parameter of a transverse-flow CW oxygen-iodine laser have been experimentally obtained for the first time from output power measurements made as a function of the cavity losses without using a CW probe laser. These measurements typically yieldalpha_{0} simeq 0.045m^-1andI_{s} simeq 0.44kW/cm²for a Cl2flow rate of1.4 times 10^{-3}mol/s with an I2flow rate of4 times 10^{-6}mol/s. The dependences of the small-signal gain and saturation parameter have been also found on the Cl2flow rate. These behaviors are qualitatively explained by a simple two-level model.     

Experimental studies of proton-implanted GaAs-AlGaAsmultiple-quantum-well modulators for low-photocurrent applications

We describe the first attempts to control photocurrent, and thus power dissipation, in surface-normal multiple-quantum-well (MQW) modulators. We have made detailed experimental studies of proton-implanted p-i-n GaAs-Al_xGa_1-xAs MQW modulators having barrier layers of x=0.3, 0.45, and 1.0. Structures were implanted to levels of 1×10¹² cm^-2, 1×10¹³ cm^-2, and 1×10¹⁴ cm ^-2. Photocurrent progressively decreased with increasing implant-dose and barrier mole fraction (x). Exciton linewidths showed a strong voltage and implant dose dependence, demonstrating a tradeoff between photocurrent and modulation performance. We obtained our best results with x=1.0 barriers. For example, 1×10¹³ cm^-2-implanted asymmetric Fabry-Perot modulators were realized in which the optical performance was similar to that of unimplanted devices. The photocurrent responsivity was, however, only 0.007 A/W at 12.5 V bias. We report measurements of carrier lifetime in these materials that show the reduction in photocurrent arises from a reduction in lifetime due to implant-induced damage. In addition, the reduced lifetime decreases the optically-excited quantum-well carrier population, leading to an increase in cw saturation intensity. Specifically, 1×10¹³ cm^-2-implanted devices with x=1.0 have a saturation intensity of roughly 45 kW/cm², while unimplanted devices have 3.5 kW/cm². Asymmetric self electro-optic effect devices (A-SEED's) are demonstrated, and power dissipation issues associated with the use of low-photocurrent modulators in integrated systems are discussed     

Gain saturation of CW laser pumped FIR laser gases

The saturation behavior of the 70 μm and the 119 μm transitions in CH3OH has been investigated both experimentally and theoretically. This knowledge is essential for constructing a complete model of the CW laser pumped FIR laser. Saturated gain measurements made in a single pass amplifier cell were found to be in good agreement with the theory of a quantum-mechanical three-level system in resonant interaction with two coherent fields. The calculation of the gain using the density matrix formalism yields a pump intensity dependent saturation, a result which is not predicted by the rate equation models.     

The effect of wall deexcitation on saturation intensity in a CO2waveguide laser

The wall deexcitation effect of the excited CO2molecule on saturation intensity in a CO2waveguide laser was experimentally investigated. The results show that a low gas pressure, saturation intensity is higher than the value predicted without wall deexcitation. The reason for this higher value is discussed.     

激光理论中的饱和效应

我们对单模激光的饱和效应进行了研究,导出了定态激光强度的平均值、方差和偏斜度的解析解。对不同光的激光理论,强度的方差没有差别;但在强度的偏斜度中,三次激光模型同实验和其他激光理论之间偏差较大。     

Measurements of unity gain cutoff frequency and saturation velocity of a GaN HEMT transistor

The measured intrinsic saturation velocity (v/sub si/) of carriers in a gallium nitride (GaN) high electron mobility transistor (HEMT) is very much lower than that predicted using Monte Carlo simulation. A novel method of extraction of the intrinsic saturation velocity (v/sub si/) of carriers has been developed utilising the deembedded s-parameters, thus enabling the calculation of v/sub si/ over a wide range of bias conditions. The method is equally applicable for gallium arsenide (GaAs) and indium phosphide (InP) based transistors. The measurements indicate for GaN-based HEMT a maximum deembedded saturation velocity of 1.1/spl times/10/sup 5/ m/s close to the pinchoff voltage (V/sub P/). It was found that self-heating had only a weak effect on the saturation velocity up to junction temperatures approaching 140/spl deg/C above ambient.     

Increased drain saturation current in ultra-thinsilicon-on-insulator (SOI) MOS transistors

Based on substrate-charge considerations, an increased drain saturation current for MOS transistors in ultrathin silicon-on-insulator (SOI) films is predicted, compared to similar transistors in bulk or thick SOI films. For typical parameters of 200-A gate oxide with a channel doping of 4×10¹⁶ cm^-3, the drain saturation current in ultrathin SOI transistors is predicted to be ~40% larger than that of bulk structures. An increase of ~30% is seen in measurements made on devices in 1000-A SOI films     

Saturation and isotopic shift of the Kr 84 excited-state transitionat 1547.825 nm

Linewidth broadening and saturation intensity measurements of the Kr 84 1s²-2p⁸ transition have been carried out with opto-galvanic spectroscopy. The Doppler-free natural linewidth of Kr 84 and Kr 83 has been determined to be 56 MHz. Transitions were observed in many other isotopes of Kr, with shifts of several GHz from the line of Kr 84     

Quantum well carrier sweep out: relation to electroabsorption andexciton saturation

The authors studied the effects of changing the barrier design of GaAs-Al_xGa_1-xAs quantum wells on the electroabsorption, exciton saturation, and carrier sweep-out times. Five samples with x values ranging from 0.2 to 0.4 and barrier thicknesses from 35 to 95 Å were studied. Within this range, the authors find that the electroabsorption is not very sensitive to the barrier thickness, but that the ionization field of the excitons approximately doubles for an increase of x from 0.2 to 0.4. The samples with high, thick barriers have lower internal quantum efficiencies than those with low, thin barriers. It was found that the exciton saturation intensity increases with increasing applied field, and decreasing barrier thickness or height. Time-resolved electroabsorption measurements confirm the variation in sweep-out rates between samples, and indicate that the escape mechanism at low field is probably a thermally-assisted tunneling process     

Influence of collisions on radiative saturation and Lamb dip formation in CO2molecular lasers

Saturated gain profile measurements in CO2at pressures where a Lamb dip appears in the laser intensity reveal that individual rotation-vibration transitions saturate with a strong Doppler component in addition to the Lorentzian holes expected for a Doppler broadened line. This mixed inhomogeneous-homogeneous behavior represents cross-relaxation effects induced by collisions that change the molecule's velocity. A rate equation formulation of collision effects elucidates the role of elastic and rotational thermalizing collisions on saturation and Lamb dip formation in molecular lasers.