Transversely excited waveguide HCN laser with UV preionization

In order to obtain high-power submillimeter-wave pulses, UV preionization was applied to the transverse discharges in HCN-laser gas mixtures. Homogeneous discharges were obtained at pressures up to 1 atm. An increase of laser output and working pressure was achieved for the 337-μm emission.     

Real-time measurements of semiconductor laser spectra

A technique for measuring the instantaneous spectrum of a semiconductor laser is described. Spectral fluctuations of several different devices, including three different length channel-substrate buried-crescent lasers emitting at 1.52 μm were examined. The shortest (100-μm) device showed a trend towaxds single-mode operation, and it is believed that devices of up to 70-μm length should emit predominantly in one longitudinal mode. Mode selection effects, thought to be due to reflections from the monitor diode, were observed in a 1.3-μm packaged laster. The technique has also been used to measure correlations between successive pulses, and between spectral width and mean position.     

Continuous self-mode locking of infrared gas lasers

Observation of continuous self-mode-locked pulses induced only by the nonlinearity of the laser medium is reported for the 10.6-μ CO2, 3.39-μ He-Ne, and 3.508-μ He-Xe laser transitions. Optical spectra of these pulses were taken with a scanning Fabry-Perot intefferometer. Attainment of self-locking was strongly dependent on the second-order spatial Fourier component of the excitation density in the optical cavity.     

Fluorescence and oscillation characteristics of LiNdP4O12lasers at 1.317 µm

Spectroscopic data and laser oscillation characteristics of the 1.317 μ line in lithium neodymium tetraphosphate (LNP) are reported. A stimulated emission cross section of this transition was spectroscopically determined as7.1 times 10^{-20}cm², which corresponds to 1/4.5 of that at the 1.047-μm transition. Cross-section temperature dependence, laser cavity loss, threshold versus crystal length, and threshold temperature dependence were measured experimentally. Since resonant loss was negligible at the 1.317 μm line, room temperature threshold is lower than that at 1.047-μm in the case of long crystal, and threshold temperature dependence is weaker than that at 1.047 μm. A miniaturized LNP laser, using a graded index fiber as a focusing medium, is also shown. LED pump intensity required to obtain a constant output is compared for 1.047- and 1.317-μm wavelengths. The 1.317-μm line seems to be useful as miniaturized optical sources in optical communication systems, since required intensity is around several W/cm²for the side pump, and the wavelength corresponds to the most transparent band of ultra low-loss optical fibers.     

Active filtering for neodymium lasers

Eleven fluorescing organic dyes were tested for their ability to alter the spectrum of a flashlamp in such a way as to increase the light intensity in one or more of the neodymium laser pump bands. A few of the dyes gave a marked improvement in the output energy of a pulsed Nd:YAG laser. Rhodamine 6G was identified as the best dye, giving better than 50 percent improvement in the laser output for 15-J 140-μs flashlamp pulses.     

Optically pumped submillimeter wave laser with Michelson interferometric output coupling

We report the performance of an optically pumped submillimeter wave laser incorporating a Michelson interferometric output coupler consisting of three mirrors and a metal mesh beam splitter. 10.33-μm radiation from a pulsed CO2TEA laser was used to pump NH3for generating submillimeter wave radiation at 281 μm. Optimum output was achieved by coupling out 59 percent of the radiation per pass using a 250-lines-per-inch mesh at a phase angle of 49°. The submillimeter laser operated in the TEM00mode and was tunable over its free spectral range of about 350 MHz. Translation of the coupling mirror allowed optimization of laser output.     

Line competition in the neutral argon laser

Uncertainties in transition assignments for the neutral argon laser lines at 1.792 and 2.208 μm have been resolved by operation of a CW neutral argon laser with several simultaneous output wavelengths. The observed competition effects have established the correct transition for the 1.792-μm line to be3d(1/2)_{1}deg -4p(3/2)_{2}and for the 2.208-μm line to be3d(1/2)_{1}deg -4p'(3/2)_{2}.     

445 Mbit/s transmission field experiment at 1.55-µm wavelength region over 80 km using undersea optical-fiber cable

New transmission equipment employing a 1.55-μm distributed feedback laser diode (DFB-LD) to overcome fiber dispersion has been tested at environmental conditions using 1.3-μm zero-dispersion fiber cable on the undersea section of route F-400M. The DFB-LD's dynamic spectrum characteristics, in relation to power penalty, were examined and a suitable laser prebias control level was obtained. Field experimental transmission lines operated error free for a two-month period, and applicability to 1.55-μm 445-Mbit/s systems of over 100 km was shown.     

High-performance single-longitudinal-mode operation of InGaAsP/InP DFB-DC-PBH LD's

The lasing performance of InGaAsP/InP distributed feedback laser diodes with double-channel planar buried heterostructure (DFB-DC-PBH LD's) is reported for end-titled and antireflection (AR) coated configuration. High-power CW single-longitudinal-mode (SLM) operation over 55-mW light output at room temperature, high-temperature CW SLM operation over 105°C, as well as stable SLM operation under 2-Gb/s high-speed direct modulation, have been attained for 1.3-μm band DFB-DC-PBH LD's. 1.5-μm band DFB-DC-PBH LD's have also exhibited excellent DFB lasing characteristics, such as high power over 20 mW and high temperature over 75°C CW SLM operation. DFB SLM yield in the laboratory was also examined for 1.3-μm DFB-DC-PBH LD's, giving rise to a good prospect for practical use in optical-fiber communication systems.     

GaInAsP semiconductor laser amplifiers for single-mode fiber communications

Gain, polarization sensitivity, saturation power, and noise characteristics of quaternary semiconductor laser amplifiers of the Fabry-Perot (FP) and traveling-wave (TW) types are reviewed. The status of antireflection coatings for TW amplifiers is presented. New results concerning the polarization sensitivity and output saturation power of a 1.5-μm buried-heterostructure (BH) amplifier are reported. A theoretical model is presented concerning the influence of the waveguide structure on the maximum internal gain of a CW-operating 1.5- μm BH amplifier, including thermal effects, and a comparison of this model with recent experimental results is reported. The influence of nonresonant losses on the noise factor of 1.5-μm amplifiers is discussed.     

Millimeter and submillimeter-wave laser action in symmetric top molecules optically pumped via perpendicular absorption bands

Ninety-nine new far infrared (FIR) laser lines from 227 μm to 1.965 mm have been observed in CH3CN, CH3CCH, CH3Cl, CH3Br,and CH3I by optically pumping these gases with CO2-laser pulses of 150-μs duration.     

Photoinitiated TEA CO laser at low temperatures

Photoinitiated discharges between continuous electrodes have been stabilized in high-pressure (CO, He, N2) laser mixtures at 100 K. A 1/2-1 device, with restricted output aperture, has yielded 1.9-J/I atm (160 torr, 100 K) in smooth 240-μs-long pulses with an efficiency of 2 percent, representing a sevenfold improvement over previous results. The unrestricted output is estimated at 5.7-J/1 atm with 6-percent efficiency.     

Influence of the lifetime and degeneracy of the4I11/2level on Nd-glass amplifiers

Gain saturation of an Nd-glass amplifier by 1.06-μm light pulses is determined by the lifetimes and degeneracies of the two laser states as well as by thermalization rates among the components of the two multiplets to which the laser levels belong. Reported are measurements showing that although small signal gain was the same for amplified microsecond and picosecond pulses, comparable energy gain saturation occurred when the energy density of the mode-locked pulses was 1.9 times smaller than the amount for the microsecond pulses indicating terminal level filling with the shorter pulses. Our measurements indicate the terminal laser level, which is one of two unresolved groups in the⁴I_{11/2}multiplet, has a lifetime greater than 50 ns and a degeneracy likely to be one or two. Pulse train distortion due to saturating amplification was measured to find whether the thermalization rates among the levels of the laser multiplets were fast or slow compared to the 10^-11-s pulses, but experimental uncertainties prohibit a determination.     

CW operation of an intracavity pumped molecular submillimeter-wave laser

The 373-μm line of CH3CN was operated in a CW mode in an arrangement where the submillimeter (SMM)-wave laser is placed inside the resonator of the CO2pump laser. 1 mW of CW output power was obtained; this is five times the power of a comparable SMM-wave laser in the common extracavity arrangement. In a pulsed mode, a peak power of 46 mW was measured.     

A 16-µm radiation source utilizing four-wave mixing in cooled parahydrogen gas

Improvements in a 16-μm radiation source based upon the combined effects of stimulated rotational Raman scattering and resonantly enhanced four-wave mixing in parahydrogen gas are described. For this source, the input waves of which are provided by temporally and spatially coincident pulsed beams from a ruby and CO2TEA laser, it was found that cooling the parahydrogen gas from 300 K to <100 K, at constant molecular density, increased the output at 16 μm by roughly a factor 4. The maximum output was measured to besim 40 muJ/pulse, which is near the theoretical limit for the 2.5 MW CO2laser intensities that were applied.     

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.     

Simple dye laser repetitively pumped by a xenon ion laser

A rhodamine 6G laser and a cresyl violet laser emit light pulses of 0.3-μs pulse length and 10-20 W peak power at a rate of 120 Hz when pumped with an inexpensive xenon ion laser.     

A high-power CO2laser radar transmitter

Experiments on the amplification of CW and pulsed infrared signals at 10.6-μ, wavelength have been carried out on CO2laser amplifiers excited by dc and pulsed electrical currents. Measurements of low signal gain, gain saturation, repetitive pulse amplification, and optical distortion have led to the design of a 1-kW average power transmitter with 10-μs infrared output pulses. The design, construction, and performance of this device are discussed. Measurements of pulse shaping, pulse-to-pulse stability, output beam divergence, and stability are outlined.     

Raman amplification of 1.50-µm laser diode light in a low fiber loss region

Raman amplification utilizing the second Stokes line of 1.32-μm Nd:YAG laser light in a single-mode silica fiber was observed. Raman gains of 24 dB have been obtained for 1.50-μm laser diode light in the low-loss region. In addition, the signal-to-noise characteristics of Raman amplification using the second Stokes line was investigated. As a result, it became clear that theS/Nratio was inferior to that in 1st Stokes line by about one order of magnitude.     

Operating characteristics and discharge conditions of a CW 28-µm water vapor laser

The operating characteristics of a CW 28-μm water vapor laser are examined for various parameters which are the discharge current, the water vapor pressure, the wall temperature of the laser tube, the mass flow rate, and the mixing ratio of helium gas or hydrogen gas. Their optimum conditions for getting a maximum output power are found. There is a relation that the maximum output power at various pressures of the water vapor is obtained at the discharge current which dissociates the water-vapor molecule rapidly.