Laser action from Ho3+, Er3+, and Tm3+in YAlO3

Laser action has been observed for the following rare-earth ions in YAlO3:Ho³⁺(sensitized with Er³⁺and Tm³⁺), Er³⁺, and Tm³⁺(sensitized with Er³⁺) at wavelengths of 2.123, 0.851, and 1.861 μm, respectively. Measurements of spectroscopic properties, fluorescence kinetics, and laser performance of these ions in YAlO3are reported.     

Electronic- and phonon-terminated laser emission from Ho3+in BaY2F8

Infrared spontaneous and stimulated emission from Ho³⁺in BaY2F8is reported. In addition to the familiar⁵I_{7} rightarrow⁵I8transition at 2 μ,⁵F_{5} rightarrow⁵I5emission at 2.4μ and⁵I_{6} rightarrow⁵I7emission at 2.9μ are discussed. There are several unusual features of the 2-μ laser emission. At room temperature, phonon-terminated laser emission is observed at 2.171 μ. At 77 K a complex CW laser output is observed in a wavelength interval lying on the shoulder of a fluorescence line. The complex output is attributed to oscillation in transverse modes of the resonator. Oscillation is not observed in the strongest emission line, despite a large terminal state splitting of 310 cm^-1. These results are explained on the basis of a theory developed earlier for transition metal ion lasers. The validity of the model is supported by demonstrating the tunability through loss modulation predicted by theory. The observation of these effects is made possible by the very low internal scattering loss in the crystals. The⁵F_{5} rightarrow⁵I5laser lines near 2.4 μ represent relatively low gain transitions with pulse durations limited by accumulation in a longer lived terminal state. The dynamics of laser emission indicate the possible absence of thermal equilibrium in the excited state. For the 2.9-μ transition the bottleneck posed by a longer lived terminal state may be eliminated by the addition of Eu³⁺or Pr³⁺, but laser emission could not be obtained.     

Self-focusing of 10.6-µm radiation in liquid CS2

Self-focusing of 9-kW CO2laser pulses was observed in liquid CS2. The calculated coefficient of nonlinear index of refraction (n2) from experimental data is approximately 10^-17MKS, which is nearly three orders of magnitude larger than the nonlinear index coefficient observed for visible radiation.     

New wavelengths of the YAlO3: Er laser

In addition to the 1.662 μm laser transition, stimulated emission at three new wavelengths at 1.677, 1.706, and 1.729μm have been observed at 300 K in the YAlO3:Er crystal with an activator concentration of 1.25 weight percent.     

Stimulated emission at 2.04 µm in Ho3+-doped ErVO4and YVO4

We have observed both CW and pulsed laser operation in Ho³⁺-doped ErVO4and YVO4at 2.0416 μm and 2.0412 μm, respectively. Both laser emissions are linearly polarized. For this preliminary experiment the crystals were cooled to liquid nitrogen temperature and pumped in two configurations using an argon-ion laser and a xenon flashlamp.     

Ho3+laser action in YAlO3at 2.119 µ

Pulsed laser action at 2.119 μ has been observed from Ho³⁺in a crystal of YAlO3sensitized with Er³⁺and Tm³⁺. A linearly polarized output of 1.2 J was obtained at 77°K. Measurements of the anisotropy of the stimulated-emission cross sections are reported.     

Oscillation of the 1.833-µ line in Nd3+:YAG

This correspondence reports oscillation of the⁴F_{32} rightarrow⁴I_{15/2}, 1.833-mutransition in Nd³⁺:YAG. PeakQ-switched output powers of 10 kW at 50 pps have been obtained.     

Broadband modulation of 3-µm light by 10-µm light in p-germanium

High-power CO2laser radiation at 1045 cm^-1is shown to enhance the room temperature transmission of p-Ge in a spectral region extending at least from 3000 to 4000 cm^-1. The interaction arises from radiation-induced changes of the hole populations within the three valence bands. Ultrafast nonradiative relaxation is responsible for the very large interaction bandwidth observed and allows the prediction of a minimum switching time of 1 ps.     

Collisionless self-focusing of CO210 µm P(20) laser light in SF6

We develop a simple intuitive picture of the vibration-rotation structure of the SF6molecule such that the molecular susceptibility responsible for self-focusing can be calculated. We treat the propagation dynamics by generalizing the standard steady-state Gaussian propagation equations to include the important effect of absorption in the wings of the spatial profile. By calibrating the model to absorption data at CO210 μmP(2)we find good agreement with beam waist data at the same wavelength. Absorption in the wings is dominant at low laser fluences, and the real part of the susceptibility is responsible for the defocusing-to-focusing turnover in the beam waist near 100 mJ/cm², consistent with the interpretation of Nowak and Ham [6].     

1.05-1.44 µm tunability and performance of the CW Nd3+:YAG laser

The Nd³⁺:YAG laser pumped by a CW 5-kW krypton arc-lamp was tuned to 19 different transitions from 1.052 to 1.444 μm by means of intracavity thin solid etalons and appropriately coated resonator mirrors. Each transition was tunable over 6-12 wavenumbers and most exhibited 10-30-W CW output, attaining 37 W at 1.319 μm and 52 W at 1.112 μm. The 1.061-μm line is 90 percent as strong as at 1.064 μm, and wavelength shift with temperature variation was measured for both. TEM00output of 20 W was available by using apertures, and compensation of thermal lensing resulted in 60 W combined TEM00+ TEM01output.     

Broadband emission and laser action of Cr3+doped zinc tungstate at 1 µm wavelength

We report on the spectroscopic properties of Cr : ZnWO4, which channels all the fluorescence into the broadband⁴T2-⁴A2transition at about 1 μm wavelength. Two different Cr³⁺centers with lifetimes of 0.5 and 5.4 μs at 300 K are analyzed. Both centers emit broad-band fluorescence with zero-phonon lines located at 834 and 877 nm wavelength. The effect of intrinsic and extrinsic charge compensation on the Cr³⁺centers is explained by a local and nonlocal compensation mechanism. With intrinsically compensated crystals we obtained CW laser action at 77 K and pulsed laser action at 300 K.     

Efficient 1.06-µm emission from InxGa1-xAs electroluminescent diodes

Vapor-grown p-n junctions of InxGa1-xAs have been prepared that emit near-bandgap infrared radiation at 1.06 µm with an external quantum efficiency in excess of 1 percent at room temperature. These diodes have an electroluminescence response time of 20 ns. In addition, InxGa1-xAs injection lasers have been fabricated with threshold current densities between 2000 and 3000 A/cm²at 80 K. The importance of internal absorption losses in determining the spectral distribution and the electroluminescence efficiency at room temperature is described.     

Three-frequency heterodyne detection of 10.6-µm laser signals

A three-frequency 10.6-μm heterodyne receiver was demonstrated experimentally. Narrow-band reception of a 40-MHz IF was realized without tracking of the carrier frequency by the local oscillator laser. A signal-to-noise ratio within 1 dB of the theoretical value was measured for large SNR.     

A highly latchup-immune 1-µm CMOS technology fabricated with 1-MeV ion implantation and self-aligned TiSi2

A 1-µm n-well CMOS technology with high latchup immunity is designed, realized, and characterized. Important features in this technology include thin epi substrate, retrograde n-well formed by 1-MeV ion implantation, As-P graded junctions, and self-aligned titanium disilicide. The 1-µm CMOS technology has been characterized by examining the deviceI-Vcurves, avalanche-breakdown voltages, subthreshold characteristics, short-channel effect, and sheet resistances. The devices fabricated by using the 1-MeV ion implantation and self-aligned titanium disilicide do not deviate from the conventional devices constructed with the same level of technology. With the As-P double-diffused LDD structure for the n-channel device, the avalanche-breakdown voltage is increased and hot-electron reliability is greatly improved. The titanium disilicide process effectively reduces the sheet resistances of the source-drain and the polysilicon gate to 3 Ω/□ compared with 150 Ω/□ of the unsilicided counterparts. The optimized 1-µm device channel n-well CMOS resulted in a propagation delay time of 150 ps with a power dissipation of 0.3 mW. With the thin epi wafers and the retrograde n-well structure, latchup immunity is found to be greatly improved. Moreover, with the titanium disilicide formation on the source-drain, the latchup holding voltage is found to be extremely high (13 V) with the substrate grounded from the backside of the wafer. If the backside substrate is not grounded, self-aligned disilicide over n⁺and p⁺regions are found necessary to ensure high latchup immunity even in the case of thin epi on heavily doped substrate. The degradation of emitter efficiency due to the TiSi2is believed to be the dominant factor in raising the holding voltage. Detailed experimental results and discussions are presented.     

CW diode-pumped Tm3+, Ho3+:YAG 2.1 ?m room-temperature laser

Room-temperature CW laser emission at 2.1?m is reported for the first time with both multimode diode arrays and single-stripe diode pumping. CW room-temperature slope efficiencies of 17% and 16% were obtained using a 100 mW multimode diode array and a 30 mW single-stripe diode, respectively. To date, CW outputs of several milliwatts at 2.1?m have been obtained.     

High-power difference-frequency generation at 4.4-5.7 µm in LiIO3

Efficient generation of high-power difference-frequency radiation, continuously tunable over the range of4.4-5.7 mum, has been achieved by mixing the Nd :YAG laser and Nd :YAG pumped infrared dye-laser outputs in LiIO3. Peak pulse powers as high as 550 kW with an average power output of 45 mW were obtained around 4.9μm.     

A study of the CW 28-µm water-vapor laser

The low signal gain of a CW water-vapor laser at 28 μm was measured as a function of the discharge current and pressure. Together with the measurement of other quantities such as the axial electric field and the concentration of OH, a partial interpretation of the mechanisms involved in pumping the 28-μm transition was possible. Thermal equilibrium between the ν0,2nu_{2}, and ν3vibrational levels will result in a large absorption at the elevated gas temperatures observed (800-1000 K). The strong dependence of gain on the electron temperature strongly suggests that the vibrational excitation proceeds through electron-impact excitation. Only the electron-impact excitation of H2O is quantitatively capable of overcoming the large thermally induced absorption. Although vibrational-excitation transfer from H2to H2O seems insufficient, by itself, to overcome this absorption, it may provide appreciable additional gain. Pumping of the 28-μm line through electron-ion recombination and by reactions involving OH can be ruled out.     

4.9-µ He-Air-CH4-(CO) laser

Low-vibrational-levelP(J)_{upsilon,upsilon'}CO laser emissions have been measured from He-air-CH4mixtures. The CW lines below 5.0μ were measured in air to occur at 4.8836, 4.8935, 4.8974, 4.9072, 4.9366, 4.9466, 4.9670, and 4.9778μ. These emissions are tentatively identified to result from transitions as low asupsilon = 3 : 2. Such emissions were relatively more frequent with CH4than with CO specifically.