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.     

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.     

The optically pumped far-infrared laser: Rate equations and diagnostic experiments

A four-level rate-equation model for an optically pumped far-infrared (FIR) laser is presented, and an expression is derived for the output power as a function of pump power and gas pressure. The theory is compared with measurements on the 570.5-μm line of CH3OH, pumped by a CO2laser. The width of the gain curve is measured and is shown to go below the Doppler width of the laser transition at low pressure. This indicates that the use of a monochromatic pump source leads to a velocity selective pumping process.     

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.     

Pump saturation in molecular far-infrared lasers

Precise absorption measurements on vibration-rotation transitions pumping far-infrared (FIR) laser transitions in HCOOH, CH3OH, CH3I and CH3F were carried out using a frequency-stabilized and intensity-controlled CO2laser. Linear absorption coefficients and saturation intensities as a function of pressure are obtained. With the help of a rate equation model it is concluded that within the pressure range relevant for CW FIR lasers the rate of deexcitation of pumped molecules is limited by rotational relaxation. For CH3F, limitation by diffusion of excited molecules to the cell wall is observed.     

Narrow-band CO2-TEA laser for efficient FIR laser pumping

To reduce the linewidth mismatch between the emission lines of a CO2-TEA laser and the absorption lines of a low-pressure FIR gain medium a tiltable Ge etalon has been introduced into the TEA resonator. The resulting spectral compression and tunability increase the energy conversion efficiency in a TEA laser pumped CH3OH laser by as much as a factor of 37 and has led to the observation of 14 new FIR laser lines.     

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.     

Quantum mechanical features of optically pumped CW FIR lasers

Quantum mechanical predictions for the gain of an optically pumped CW FIR laser are presented for cases in which one or both of the pump and FIR transitions are pressure or Doppler broadened. The results are compared to those based on the rate equation model. Some of the quantum mechanical predictions are verified in CH3OH.     

Far-infrared raman laser with high intensity laser pumping

Theoretical and experimental results are presented for a pulsed far-infrared (FIR) molecular gas laser with high intensity laser pumping. In these FIR lasers, high intensity pumping is found to produce stimulated Raman emission at very large offsets (up to 30 GHz) from resonance with the intermediate state. A theoretical, density matrix model is developed for these lasers to account for simultaneous Raman emission on rotational levels in the ground and excited vibrational states (double Raman resonance). This theoretical approach is necessary in the case of off-resonant, high intensity pumping. Theory predicts the FIR emission frequency, the FIR laser gain, and the pump threshold intensity as a function of pump laser frequency. Experimental results are obtained onP-,Q-, andR-branch transitions in¹²CH3F and¹³CH3F using a single-mode, grating tuned CO2TEA pump laser with an intensity of up to 40 MW/cm². Good agreement is obtained between theory and experiment for the observed values of FIR emission frequency and pump threshold intensity. These results indicate that a widely tunable (150-1200 mum), pulsed FIR CH3F laser could be constructed with a tunable, multiatmospheric CO2pump laser of modest power (about 2-5 MW).     

A 500 MHz tunable CO2waveguide laser for optical pumping

A long-pulse CO2waveguide laser is described, which can be single frequency tuned over 500 MHz in about 80 lines. A peak power reaching 125 W at line center and 85 W at the tuning edge in the strongest lines makes the laser ideally suited for optically pumped FIR lasers. New FIR lines have been observed by pumping CH3OH in absorptions located up to 268 MHz from the CO2line center. FIR wavelengths have been measured, identified, and compared to calculations at a level of relative accuracy of5 cdot 10^{-5}.     

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.     

Far-infrared CW Raman and laser gain of14NH3

The FIR Raman and laser gain properties of¹⁴NH3optically pumped by the CO29R(30)and the N2O10P(13)laser lines, respectively, have been measured and calculated using the quantum mechanical theory of three-level systems. The laser gain is about two orders of magnitude higher than for usual FIR laser transitions. The Raman gain shows two features characteristic for the two-photon process: extremely high saturation intensity and high pressure maximum. Very satisfactory agreement between theoretically calculated and experimentally measured gain properties is found.     

A tunable far infrared laser

A continuously tunable far infrared (FIR) laser has been demonstrated; experimental results are presented. A high-pressure (10-12 atm) continuously tunable CO2TE laser is used to pump Raman transitions in CH3F; the generation of continuously tunable radiation in the250-300 mum wavelength range is reported. Accurate frequency and bandwidth measurements have been made and the FIR bandwidth in superradiant emission isapprox4-5GHz. Consequently, the generation of frequency tunable, subnanosecond pulses in the FIR appears feasible. The generation of tunable laser radiation from 150 to 1000 μm by stimulated Raman scattering should be possible using higher pump intensity and/or other gases.     

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.     

New FIR laser lines from optically pumped CH3OH: Measurements and assignments

26 new FIR laser lines have been observed in CO2laser pumped CH3OH, and together with some previously observed lines their wavelengths have been measured with a relative accuracy of3 times 10^{-4}by using the FIR resonator as a scanning Fabry-Perot interferometer. Based on the internal consistency of the data, it is suggested that a number of the lines originate from combination bands involving simultaneous excitation of the CO stretch mode and a different vibrational mode.     

Observation and assignment of D218O FIR laserlines optically pumped by a waveguide CO2 laser

By means of a detailed analysis of the v₂ infrared band of D₂¹⁸O, it has been possible to assign most of the FIR emissions reported in the literature. Moreover, two FIR laser lines which fall in the range of tunability of the CW waveguide CO₂ laser have been predicted and observed. The frequency of the stronger line was measured and found to be 2611.4185(10) GHz, thus filling a gap in the presently available comb of FIR laser lines whose frequencies have been measured. The wavelength precision of the assigned lines was improved by about two orders of magnitude     

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.     

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.     

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.     

Analysis of CH3OH far infrared laser lines optically pumped by sequence band and isotopic CO2lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH3OH pumped by theS-9P(31),18-10R(24),13-9R(26), and13-9P(16)CO2laser lines, plus an interesting speculation for the FIR line pumped by the18-9P(12)CO2line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm^-1from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three¹⁶O¹²C¹⁸O laser lines.