Observation of new FIR superradiant lines from optically pumped D2O

Four new laser lines from optically pumped D2O vapor are reported at wavelengths of 235 μm, 280 μm, 97 μm, and 98 μm, the latter having a quantum conversion efficiency of 38 percent.     

Efficient multikilowatt mid infrared difference frequency generation in CdGeAs2

Multikilowatt mid infrared emission with high pump photon conversion efficiency (∼ 15 percent) has been obtained by difference frequency generation in CdGeAs2utilizing the double wavelength output from a grating tuned twin-cavity TEA CO2system, one signal of which is frequency doubled to provide efficient synchronized sources for both pump and idler. Tuning over a spectral range8-14 mum can be achieved and further extended to 17 μm using 12.8 μm emission from an efficient TEA CO2pumped NH3laser.     

Efficient luminescence band created in (Al, Ga)As multilayers by athermal laser processing

A new luminescence band is observed in (Al, Ga)As three-layer structures which were subjected to well-controlled CW Krion laser irradiation at power densities of 0.55 MW/cm². The new band is shifted by 90 meV to lower energies with respect to the band-to-band recombination. The total photoluminescence efficiency at room temperature can be improved by as much as 80 percent. Measurements of the luminescence at 0.8 μm and of the infrared (IR) power emitted at 3.1 μm have been performed during processing. Maximum temperature rises of320-350degC for the laser heated zone have been evaluated from these measurements. The well-defined laser threshold power, necessary to create the new luminescence centers, does not depend on the substrate temperature in the range of20-250degC. It does increase linearly with decreasing laser photon energy.     

New efficient CW far-infrared optically pumped CH2F2laser

Far-infrared laser action is reported for the first time from the optically pumped CH2F2molecule. Lasing on twelve FIR transitions was produced by pumping with six emission lines in theRbranch of the 9.6 μm band of the CW CO2laser. High conversion efficiencies of up to 20 percent of the quantum limit have been obtained with the stronger FIR laser lines.     

The infrared N2laser as a pump for IR dyes

An infrared molecular nitrogen laser cooled by liquid nitrogen was used to pump a simple grating tuned infrared dye laser in the wavelength range from 0.915 μm to 1.04 μm. Broad-band operation of the dye lasers produced efficiencies as high as 20 percent, and produced output at wavelengths as long as 1.096 μm.     

Multicomponent solid-solution semiconductor lasers

Properties of a new hetetrostructure based on quaternary alloys are presented in application to semiconductor lasers. Room temperature laser operation is obtained near 1.06 and 1.8 μm with injection pumping and near 2 μm with electron-beam pumping.     

A simple first positive system nitrogen laser for use in optical fiber measurements

A near infrared laser operating on several transitions of the first positive system of N2was developed for measurements associated with optical fibers. The laser features a simple, longitudinal, segmented design giving pulsewidths of 60 to 80 ns full width at half maximum (FWHM) and peak powers of over 600 W in the 0.86 to 0.89 μm region in addition to significant output near 1.04 and 1.23 μm. Backscatter-reflection returns from optical fibers have been obtained using the laser.     

Optical surface wave mode converters and modulators utilizing static strain-optic effects

Periodic perturbations of dielectric waveguides can be obtained by an evaporated SiO2thin film grating through the static strain-optic effect. These waveguides are applied to TE-TM mode converters and modulators in Ti-diffused LiNbO3waveguides. Using a coupling length of 3 mm in an optical surface waveguide, we have demonstrated a TE-TM mode conversion efficiency of 80 percent and a TE-TM mode modulator with 100 percent modulation with an applied field of 2 V/μm. A theoretical analysis of a reflector for a semiconductor laser waveguide is also described.     

An Efficient High-energy Pulsed NH<Subscript>3</Subscript> Terahertz Laser

Experimental studies on an efficient high-energy pulsed NH₃ terahertz (THz) laser pumped by a TEA CO₂ laser are presented. Pulsed THz radiation of 204 mJ with a wavelength of 151.5 μm was generated from an ammonia laser pumped by a 32 J TEA CO₂ laser tuned to the 10P(32) transition, and the photon conversion efficiency of 18% was achieved, in which the pulsed energy was measured by pyroelectric detectors. Meanwhile, the THz transmittance was measured and compared for 5 kinds of materials. Finally, regarding the THz transmittance of these materials, a phenomenon for ammonia radiations with 91 μm and 152 μm pumped by a 9R(14) line was observed: i.e. while the 152 μm THz radiation can win in competition for gain at lower pressure, the 91 μm THz radiation in contrast can prevail at higher pressure.     

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.     

Optical single sideband generation at 10.6 µm

The indicatrix ellipsoid of an electrooptic crystal with a threefold rotation axis under the influence of an applied microwave field circularly polarized in a plane normal to the axis intersects this plane in a rotating ellipse of constant shape. A circularly polarized optical field in this plane produces an electric polarization at one sideband frequency only, upshifted if the optical field rotates in the opposite direction the indicatrix rotates, downshifted if the rotations are the same. Ideally, 100 percent conversion of the optical incident field into the up- or downshifted field may be achieved. A square waveguide containing a CdTe crystal is investigated as the structure appropriate for phase-matched single sideband conversion. Experiments are reported yielding a 67 percent conversion efficiency for shifting 10.6 μm laser radiation by 17 GHz. The efficiency was limited by crystal length and/or microwave breakdown. For longer crystals conversion efficiencies approaching 100 percent are extrapolated. Scaling laws for other microwave and laser frequencies are presented.     

High-efficiency, high-power difference-frequency generation at 2-4 µm in LiNbO3

High-efficiency generation of high-peak power and high-average power difference-frequency radiation, continuously tunable over the range of 2 to 4 μm, has been achieved by mixing the Nd:YAG laser radiation with the output of a near-infrared dye laser pumped by the second harmonic of the same Nd:YAG laser in LiNbO3. A peak power as high as 1.6 MW with an average power of 130 mW was obtained near 2.3 μm.     

Transmission characteristics of long spliced graded-index optical fibers at 1.27µm

Transmission characteristics of graded-index fibers at 1.27 μm are investigated. Bandwidth measurements are made in the frequency domain by using a CW GaInAsP laser diode modulated by a sinusoidal signal. For a germanium pbosphosilicate fiber, the optimum index profile at 1.27 μm is determined as 1.98. It is shown that optimum profile at 0.83 μm is 2.08 and there exists a large profile dispersion effect: for example, the experimental maximum 3-dB bandwidth at 1.27 μm decreases to one-third at 0.83 μm. Length dependence of bandwidth is investigated for 48 km long spliced graded-index fibers at 1.27 μm. It is verified that using a simplified transmission model in which mode conversion is assumed at splicing points, the bandwidths of long spliced fibers are predicted with satisfactory accuracy in terms of unit fiber transfer functions.     

Optical pumping by CO2and N2O lasers: New CW FIR emissions in 1,1-difluoroethane

53 new CW FIR laser lines are reported in 1,1-difluoroethane optically pumped near 10 μm by CO2and N2O lasers. The emission spectrum initially reported in the literature consisted of four lines between 770 and 458 μm and has now been extended to the 2.39 mm- 319 μm region. The reason for this extension, especially to the long wavelengths, is analyzed.     

Initiation of a pulsed HF laser with a CO2laser-produced plasma

A CO2laser-produced plasma was used to initiate an HF chemical laser. It was found that fluorine atoms produced by the thermal dissociation of CF4in the hot plasma rapidly diffused from the focal volume and chemically reacted with the surrounding hydrogen gas to produce excited HF molecules. Output powers greater than 500 W at 2.79 μm and small-signal gains greater than 6 percent/cm at 2.73 μm were observed. This method of chemical laser initiation should be compatible with a wide variety of reaction systems.     

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.     

Planar stripe with waist and/or notch (SWAN) injection laser

This paper describes a novel planar stripe-geometry injection laser (referred as SWAN laser) showing a single transverse and longitudinal mode operation made by a simple fabrication method. This stripe-geometry is composed of a main stripe section with the width of around 10 μm and mode control section with the nominal width near to carrier diffusion length, less than 5 μm, a shape of which looks like waist(s) and/or notch(es) along the stripe. A "kink", which often appears in the relation between a light output and a current in conventional planar injection lasers, is not observed at the power level of more than 20 mw/ facet. The laser has advantage of controlling modulation dynamics by the shape of waist(s) and/or notch(es) along the stripe that enables control of the lateral carrier diffusion profile in the vicinity of an active layer and the amount of spontaneous emission into laser mode.     

Characteristics of room-temperature 2.3-µm laser emission from tm3+in YAG and YAlO3

The relaxation of low-lying excited states of Tm³⁺ions doped in YAG, YAlO3, and Y2O3due to photon and phonon emission is studied theoretically. Stimulated emission cross sections (integrated over frequency), fluorescence lifetimes, and radiative quantum efficiencies are calculated and their implications for laser operation on the 2.3-μm³F4→³H5line of Tm³⁺are discussed. The calculations, based on a few phenomenological parameters which have been determined by others, are easily generalizable to other host materials and other rare-earth (RE) ions. Room-temperature pulsed laser emission from Tm³⁺ions near 2.3 μm was observed on one line in Tm:Cr:YAG, and on four lines in Tm:Cr:YAlO3. Lower oscillation thresholds were generally obtained in the YAlO3 rods, consistent with the theory presented. A threshold of 31 J was obtained with a Tm:Cr:YAlO3rod at 2.274 μm. In the free-running pulsed mode, peak power levels up to several hundred watts and total output energies up to 12 mJ/pulse were observed. Other general, observed operating characteristics are discussed.     

Optical performance of the Los Alamos free-electron laser

During a year of oscillator experiments, the Los Alamos free-electron laser has demonstrated high-power and diffraction-limited output capabilities with a factor-of-4 wavelength tunability in the infrared. A conventional,L-band RF linear accelerator produced a 100 μs long, 2000 pulse train of 35 ps wide electron-beam pulses with peak currents to 50 A and nominal energy of 20 MeV. Small-signal gain in excess of 40 percent was generated in a 1 m, plane-polarized, uniform-period undulator for wavelengths between 9 and 11 μm. Best performance included an electron-energy extraction efficiency of 1 percent, 10 MW peak output power, and a corresponding average power of 6 kW over a 90 μs pulse train. A Strehl ratio of 0.9 characterized the output spatial beam quality. By reducing the electron energy by a factor of 2, the wavelength was tuned continuously from 9 to 35 μm.     

Pulse chirping in a Nd:YAG laser

The 1.06-μm output of a loss-modulation mode-locked and frequency-doubled Nd:YAG laser was examined using a microwave avalanche photodiode with a rise time of ∼40 ps, and a scanning Fabry-Perot. The pulses were found to be transform limited only in the case where the 0.53-μm output of the laser was suppressed. When conversion efficiency was restored, the spectrum exhibited narrowing, but the pulses were much wider than the transform limit, indicating the presence of chirping.