The effect of mid-infrared and far-infrared emission,generated at NH3 excitation by intense radiation of a TEA CO2 laser,on ammonia absorption

The effect of Mid-InfraRed (MIR) ( 12 m) and Far-InfraRed (FIR) ( 100 m) emission from excited ammonia on the absorption of intense radiation of a TEA CO₂ laser has been studied experimentally under collisional and collisionless excitation conditions with ammonia pressures from 0.5 to 0.03 Torr. The energy of MIR and FIR emission was studied as a function of NH₃ pressure and laser energy fluence. Particular emphasis was given to the kinetics of MIR and FIR emission generation at different NH₃ pressures and to the measurement of the time delay of re-emitted pulses relative to the exciting CO₂ laser pulse. It has been found that the re-emission in the MIR range is highly collisional in nature. The intensity of MIR emission drops sharply (asp ³) with decreasing NH₃ pressure and its delay time relative to the exciting laser pulse increases. At the same time, re-emission in the FIR range (in the case of resonant excitation of NH3 at the 9R (30) line of CO₂ laser) is observed during an exciting pulse up top < 0.03 Torr. When binding the rotational sub-levels of a molecule with transitions, FIR emission acts as rotational relaxation and thus leads to an increase in NH₃ IR absorption even at collisionless excitation.     

New CW FIR laser lines obtained in ammonia pumped by a CO2 laser, using the Stark tuning method

We report fifty seven CW FIR emissions observed in NH₃, by resonant pumping with a CO₂ laser. Exact coincidences between IR absorption lines of the gas and emission lines of the CO₂ laser have been carried out by Stark tuning. IR frequency shifts, up to 30 GHz, have allowed the pumping of forty three NH₃ transitions.These FIR emissions correspond to thirty one different wavelengths in the 50–400 m range; eighteen ones of them are new emitted wavelengths by pumping with the CO₂ laser.     

Compact, high power FIR NH3 laser pumped in a three mirror CO2 laser cavity

A compact CO₂–NH₃ FIR laser system where an NH₃ laser cavity was inserted in pump, three mirror CO₂ laser cavity was designed. The total length of this system was about 1.8 m. Output energy of about 1 mJ (10 KW pea power) was obtained at the 152 m and 90 m lines in NH₃. Power conversion efficiency of 1.7 percent was obtained at the 90 m line.     

CW and pulsed FIR-CO2 hybrid laser with improved efficiency and amplitude stability at short FIR wavelengths

For the first time stable cw output of a FIR-CO₂ hybrid laser has been achieved at wavelengths shorter than 300 m. Due to the saturable absorber characteristic of the FIR laser gas, cw or pulsed emission is observed on both, the CO₂ and the FIR laser output, depending on the operating conditions. Results are reported on different resonant lines in CH₃OH and the 67 m Raman line in NH₃. The good efficiency of this laser is also demonstrated by the excitation of two new emission lines in CH₃OH, namely 49 and 56 m, pumped by 9R(22) and 9R(24), respectively.On leave from the Institute of Physics, University of Beograd YU-11000, Beograd, Yugoslavia     

High power FIR NH3 laser using a folded resonator

A compact FIR laser cavity having a couple of folding mirrors was designed. By inserting this FIR cavity into the pump TE CO₂ laser resonator, we observed 19 FIR NH₃ laser lines of which 4 new lines were included. The maximum output power was over 500 W at 90 m.     

FIR NH3 cascade laser excited by a Q-switch laser

Short FIR laser pulses of high repetition rate are obtained by pumping NH₃ with the pulses of a passively Q-switched IR laser. The two cascade laser transitions observed show coupled relaxation oscillations. The pulse shapes and delay times are qualitatively in agreement with a four-level rate-equation model.Partially supported by Deutsche ForschungsgemeinschaftOn leave from Korea Standards Research Institute, Dae Deog Dan Ji, P.O. Box 3, Choong Nam, Korea, supported by Korea Science and Engineering Foundation     

Interaction enhancement of Raman processes in miniature opfirl

In miniature optically pumped FIR laser, NH₃ molecules pumped by CO₂ 9R(16) produce a pair of FIR Raman transition: saP(7,0) and aaP(7,1), which are very close in frequency. When the operating gas pressure is high, the interaction enhancement effect occurs, making the FIR output enhance very much.     

The Spectrum of Ground-State Reversed Transition of CH3OH Far-Infrared Laser

Using the CH₃OH molecular energy levels data base management program, we deduced that when a CH₃OH laser pumped by CO₂-9P(16) line, there should be a FIR laser line of 918m wavelength, which corresponding to a transition in ground-state reversed three-level energy system. For the first time, the spectra of ground-state reversed three-level system transitions were calculated by solving the density matrix equations, and the spectrum characteristics of 918m line were studied. Experimentally, the CH₃OH FIR laser line of 918m wavelength was obtained by pumping with a TEA-CO₂ laser. The experimental results were in good agreement with the theoretical calculations.     

Infrared and far-infrared laser emissions from a TE CO2 laser pumped NH3 gas

In this paper, infrared (IR) and far-infrared (FIR) laser emissions from a TE CO₂ laser pumped NH₃ gas are reported. 8 IR laser emissions near the wavelength of 12 μm were observed by using 4 different CO₂ laser lines for the pumping. 3 IR laser emissions in P-branch of vibrational-rotational band (ν₂ → G) oscillated simultaneously in two pumping cases, i.e. pumping with the R(30) or R(16) line of 9.4 μm band from the CO₂ laser. 26 FIR laser emissions (26.45 μm ～ 281.0 μm) were observed by using 12 different CO₂ laser lines, and the 10 FIR emissions of them may be new laser emissions as far as we know.     

New FIR laser lines from CD3OD optically pumped by a CO2 waveguide laser

In this work we report new FIR laser lines from CD₃OD optically pumped by a CO₂ waveguide laser. The wide tunability of this laser (290 MHz) makes it possible to pump absorption lines with large frequency offset relative to the CO₂ laser line center, which are not possible by using conventional CO₂ lasers. As a consequence 19 new laser lines have been discovered, ranging from 38.0 m to 455.2 m in wavelength. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorber CD₃OD line were performed using the transferred Lamb-dip technique. We also present direct Doppler-free offset measurements of infrared absorption, obtained within the FIR laser cavity itself, using optoacoustic detection.Work supported by FAPESP, CNPq, FAP-Brasil and CNR-Italy     

FIR Stark spectroscopy on optically pumped CH3OH laser

An extensive theoretical and experimental analysis of the absorption and emission spectrum of a CH₃OH FIR-laser excited by a conventional CO₂ laser is presented. Particular interest is devoted to the Stark shifts of the pump and lasing lines and to the electric field dependence of the Fir-laser output of the various lines. The offsets with respect to the exciting radiation and the Stark shifts of the IR absorption (pump) lines are measured by means of the transferred Lamb dip technique. The theoretical behaviours of the Stark patterns are calculated for several choices of the quantum numbers and selection rules involved in the transitions. A large variety of experimental results are reported and compared to theory. Non-linear Stark shifts have been observed for the 37.5m FIR laser line and for the IR-pump transitions excited by the 9-P(38) and 10-R(38) CO₂ laser Lines. Line assignments are proposed and new FIR laser lines are reported.     

Optically pumped submillimeter laser lines from CH2F2 and CD2Cl2 using a12C18O2 CW laser

Thirty-nine new submillimetre laser lines in CH₂F₂ and twelve in CD₂Cl₂ have been obtained in a Fabry-Perot FIR resonator by optically pumping with a CW¹²C¹⁸O₂ laser. The wavelength range obtained for CH₂F₂ is 126m to 1091m and for CD₂Cl₂ 212m to 774m. The wavelength measurements are accurate to within 5.10^–3. The relative polarisations of the pump laser and the FIR laser output were also determined. Tentative assignments of the IR and FIR transitions were made using existing microwave data.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 m–1200 m range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^–4–10^–3 accuracy is achieved in the measurement of the FIR wavelengths.The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^–1 of this main isotope.     

New Optically Pumped FIR Laser Lines and Frequency Measurements from CH3OD

This work reports the discovery of 45 new optically pumped far-infrared (FIR) laser lines from CH₃OD in the range 42.6 m to 207.2 m. A highly efficient CO₂ laser was used as the pump laser for an Optically-pumped Fabry-Perot FIR laser. The frequencies of most of the new lines were measured in the range 1.7 to 6.4 THz. Twenty-eight CO₂ lines were used as pump lines; nineteen of these had frequencies lower than those previously used to pump CH₃OD in a FIR laser. Sixteen of the new FIR lines had absorption transitions which belong to the OD bending vibrational mode.     

New FIR Laser Lines and Frequency Measurements of CD3OD

The isotopomer of methanol, CD₃OD, was optically pumped by a cw CO₂ laser resulting in 53 new far-infrared (FIR) laser lines. The wavelengths are in the range 42.9 m to 189.9 m with the majority below 100 m. Ten different CO₂ lines were used for the first time to pump CD₃OD yielding new FIR laser lines. Some of the CO₂ pump lines belong to the hot-bands and sequence-bands of CO₂ in the 10 m region. The frequency was measured for 40 FIR laser lines in the range 1.5 THz to 6.9 THz, 32 of which were new laser lines.     

Amplification and measurement of single 1.6–3.5 ps Pulses generated by a distributed feedback dye laser

Twenty FIR laser lines with wavelengths between 146 and 2000 m have been observed from deuterated formyl fluoride (DCOF) optically pumped with isotopic CO₂ lasers. Tunable diode laser measurements on thev ₄ band of DCOF were combined with earlier high precision spectroscopic data on thev ₃ andv ₄ bands, and enabled identification of the transitions responsible for 9 of the new FIR lines.     

Optically pumped14NH3 laser and its stark tuning at 10.78 μm

Infrared (ir) emissions from a TEA-CO₂-laser-pumped NH₃ laser are reported. Superfluorescent emissions and selective single-line oscillations have been obtained in the range from 11 to 13 m. The results make possible the design of a NH₃ Stark cell allowing a 1 GHz shift of the 10.78 m NH₃ emission line.     

Self-focusing and defocusing of TEA CO2 laser radiation in NH3

We report on the observation of self-focusing and defocusing of TEA CO₂-laser pulses in NH₃. Self-focusing of the 9R(30) CO₂ laser line resulted in a significant spatial narrowing of the laser beam after propagating through a 100 cm long cell containing NH₃ at a relatively low pressure of 1 Torr. Spatial broadening, characteristics of self-defocusing, has been observed for the 9R(16) CO₂-laser line.