Diffraction limited CW optically pumped lasers

The far infrared spectral characteristics of inductive metal mesh dielectric hybrid mirrors were investigated. From experimental and theoretical studies, the mirrors were found to exhibit etalon effects due to the finite Si substrate thickness and to have two separate diffraction conditions. With grid spacinggand substrate index of refractionn, forn^{-1} < g/lambda < 1the mirrors diffract in transmission while forg/lambda > 1the mirrors diffract both in transmission and reflection. Using both inductive and capacitive mesh mirrors, EH11outputs have been obtained at the milliwatt level in the range 70 μm to 1.2 mm. Powers in excess of 10 mW were obtained from CH3OH at 96 and 118 μm, HCOOH at 393 μm, CH3I at 447 μm, and CH3F at 496μm.     

High-efficiency driven Q switching of the CO2laser using the stark effect in molecular gases

High-efficiency drivenQswitching of the CO2laser has been observed by the use of the Stark effect in CH3Cl, CH3F, CH3CHF2, CH2= CF2, and C2H3Cl on various lines in both the 9.4- and 10.4-μ bands. The effect is observed with both pulsed and sinusoidal electric fields applied to the intracavity modulator.     

New optically pumped CW submillimeter emission lines from OCS CH3OH and CH3OD

A new emission line has been observed by optically pumping OCS with 9 μm R(8) CO2laser radiation and has been tentatively assigned. In addition, fourteen new emission lines of CH3OD and four of CH3OH have been discovered.     

Pulsed high-power far-infrared gas lasers: Performance and spectral survey

We describe the practical performance of a pulsed mirrorless far-infrared gas laser pumped by a TEA CO2laser. The system is designed to serve as a high-power source for experiments in far-infrared nonlinear optics and saturation spectroscopy of solids. Out of numerous candidates, 11 gases were selected for a careful survey: CH3F,¹³CH3F, NH3, D2O, D2¹⁸O, D2S, HDS, CH3Cl, CH3Br, CH3I, and CH3CN. With an available pump energy of up to 10 J, a total of 203 far-infrared lines with pulse energies up to 12 mJ were found, covering the wavelength range from 42 μm to 1.2 mm. 78 of these lines had not been observed before. The position of further 39 lines is at variance with former literature reports.     

PassiveQswitching of the CO2laser by C2H4gas and CH3OH vapor

PassiveQswitching of the CO2laser in the 10.6-μ region using C2H4gas and in the 9.6-μ region using CH3OH vapor is reported.     

High power optically pumped far infrared laser systems

Single mode, 60-80 ns pulse width, 50-70 kW peak power laser oscillators operating on the 384.6 μm line of D2O have been developed. The characteristic linewidths of these oscillators are less than 25 MHz full width at half maximum which favorably compares with the intrinsic width of 6-8 MHz associated with the pulse length of about 60 ns. A 12.7 mJ, 195 kW, 384.6μm D2O laser oscillator-amplifier combination has been constructed and tested. Although single longitudinal mode operation is attained from this oscillator-amplifier system, amplified spontaneous emission (superradiance) from the amplifier adds low power level wide-bandwidth background radiation. Studies of far infrared lasing action in CH3F and CH3I are also described.     

New far-infrared laser lines from CO2-laser-pumped CH3OH gas by using a copper waveguide cavity

Eleven new far-infrared (FIR) laser lines have been observed from CH3OH pumped by a CO2laser. These lines are ranged from 78 to 694 μm and are obtained by using a copper waveguide cavity.     

Simultaneous HCN and H2O laser emission in mixtures containing H, C, N, and O

Simultaneous laser emission at 337 and 118 μ has been observed in a pulsed discharge through a mixture of N2, O2, and either CH4or (C2H5)2O. Earlier observation of a laser line at 469 μ is rejected and explained.     

Far-infrared distributed feedback gas laser

Theory and first operation of a distributed feedback gas laser is expanded. This goal has been achieved by an optically pumped 496μm CH3F laser equipped with a hollow metal waveguide with deep periodic corrugations. The period of corrugations is tuned by temperature variation. Single-mode operation is achieved. The working pressure of CH3F is up to 10 torr. Propagation of the laser beam is near the diffraction limit. The spectral linewidth of less than 22 MHz corresponds to the transform limit set by the 50 ns pulse duration. Temperature tuning curves of the laser output are in good agreement with theory.     

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.     

Laser pumped molecular lasers--Part I: Theory

The density matrix formalism describing the interaction between a three level molecular system and two nearly resonant laser fields of arbitrary intensity is extended to include the molecularM-level degeneracy. Expressions for gain on the two possible relative polarizations of a laser pumped molecular laser are derived and its saturation behavior discussed. Numerical results for the 385 μm transition in D2O and 496 μm transition in CH3F are presented.     

Far infrared frequency synthesis with stabilized CO2lasers: Accurate measurements of the water vapor and methyl alcohol laser frequencies

A far infrared (FIR) frequency synthesis technique using saturated-absorption stabilized CO2lasers and a point-contact diode has been used to measure frequencies of a number of strong CW H2O, D2O, and CH3OH laser lines. The first frequency measurements of the 79-μm H2O, the 73- and 108-μm D2O, and 11 CO2-pumped CW¹²CH2¹⁶OH laser lines are reported. This measurement is the first demonstration of the general usefulness of CO2lasers for accurate synthesis of FIR frequencies.     

Very short far-infrared pulses from optically pumped CH3OH/D, CH3F, and HCOOH lasers using an EQ-switched CO2laser as a pump source

Very short far-infrared (FIR) pulses were generated from optically pumped CH3F, CH3OH/D, and HCOOH lasers using aQ- switched, current pulsed (200 mA, 100 μs), low pressure (20 torr) CO2laser as a pump source. Values of 20 ns for the rise time and 50 ns for the decay time of the FIR pulses have been observed. The dependence of the FIR pulse shape parameters, i.e., rise time, decay time, and pulse buildup time, on the width of the pump pulse and the pressure of the molecular gas have been investigated experimentally. Due to the regular pulse shape, high repetition rate (350 Hz), high peak power (≳1 W), and broad spectral range (lambda = 100-500 mum), the pulses are very useful for purposes of solid-state and molecular time resolved spectroscopy.     

Observation and assignment of large offset farinfrared laser lines in CH3OH optically pumped by a CO2waveguide laser

Four new FIR laser lines at 62.98, 48.77, 224.53, and 190.65 μm are reported from CH3OH, optically pumped by the 10R34 and 9R10 lines of a waveguide CO2laser. Measurements performed by several techniques confirm that the pump offsets are outside the tuning range of conventional CO2lasers. Two of the lines are assigned as highJtransitions within the torsional ground state of the CO stretch.     

Stark effect applicable to optically pumped far-infrared laser

The effect of low electric field Stark tuning on the absorption of CH3OH gas at theP(12) 9.4-muCO2laser line has been studied. At the 220-mtorr CH3OH pressure optimal for CH3OH far-infrared (FIR) laser operation, the line center absorption coefficient increases by a factor of 5 with a Stark field of 2.3 kV/cm.     

A high-intensity narrow bandwidth pulsed submillimeter laser for plasma diagnostics

A CH3F laser oscillator producing between 0.5 and 1 kW pulses lasting 400 ns and confined to less than 27-MHz bandwidth at 496 μm is the basis of an injection laser assembly which generates up to 250 kW of far-infrared (FIR) output within a bandwidth of 55 MHz.     

Assignments of the high power optically pumped CW laser lines of CH3OH

Thirteen far IR laser lines in CH3OH, optically pumped by a CO2laser, have been assigned toa- andb-type transitions in ν5CO-stretch band. Identification procedures used were: a frequency match between the CO2pump and CH3OH absorption, frequency match of laser lines and CH3OH ν5transitions, polarization of far IR radiation, cascade and competition effects between far IR laser lines, and frequency consistencies. An improved set of molecular constants for ν5transitions were also obtained.     

New CW FIR laser action by Stark tuning from optically pumped CH3OH and CH3OD

Fifteen new CW FIR laser lines are reported from Stark tuned CO2optically pumped CH3OH and CH3OD. Four new CW laser lines have also been observed from zero field optically pumped CH3OD, three with a CO2laser, and one with an N2O laser.     

Submillimeter laser action of CW optically pumped CD2Cl2, CH2DOH, and CHD2OH

More than 30 laser lines, several of them with an intensity in the order of mW have been obtained in the submillimeter wavelength range from 100 to 900 μm by optically pumping the deuterated molecules of dichloromethane (CD2Cl2) and methanol (CD2HOH, CH2DOH) with a step tunable CO2laser.     

An optical-fiber-based gas sensor for remote absorption measurement of low-level CH4gas in the near-infrared region

A long-distance low-loss silica optical-fiber link connected to a compact absorption cell was employed to realize a fully optical highly sensitive fiber gas sensor for low-level CH4gas in conjunction with a highly radiant InGaAsP light-emitting diode (LED) at 1.66 μm. By using a dielectric interference filter which replaces a monochromator to simplify the system configuration and operation, a 2-km-long silica fiber link was demonstrated to be capable of achieving reproducibly the detection sensitivity of nearly 700 ppm for CH4gas in air, i.e., 1.3 percent of the lower explosion limit of CH4density. This high sensitivity verifies a potential for major applications to strategic points within the environment, like industrial and mining complexes as well as urban and residential areas. This result also indicates that the purely optical gas-sensor system based on ultralow loss optical-fiber networks, incorporating LED's or laser diodes, can be extensively utilized for the real-time remote measurement and surveillance of a number of dangerous, explosive, and toxic gases in the near-infrared region.