New far infrared laser lines in optically pumped CD3F

Summary Using a high pressure CO₂-laser we have studied laser action in¹²CD₃F stimulated by R-branch pumping. We used an arrangement with low-feedback mirrors as suitable for Raman laser action. However, no Raman laser action has been observed in¹²CD₃F though similar experimental conditions were met as for¹²CH₃F and¹³CH₃F. The reason for the different behavior of the gases is not yet clear.Instead of Raman laser action we found 15 FIR resonant laser lines with 13 of them unknown up to now in the frequency range from 50 cm^–1 to 68 cm^–1. We reached FIR pulse energies up to 900 J, corresponding to a photon conversion efficiency of 12%. For our arrangement the optimum operation pressure varied from 40 torr at low J values (J=36) to 70 torr at high J values (J=49).     

12CH3OH and 13CH3OH optically pumped by the 10P and 10HP bands of a pulsed CO2 laser: New far-infrared laser emissions and assignments

We have re-investigated the ¹²CH₃OH and the ¹³CH₃OH molecules as optically pumped far-infrared laser sources. We have used our new waveguide pulsed-high-peak-power CO₂ laser for pumping, finding 20 new far-infrared laser lines emitted by ¹²CH₃OH and seven emitted by ¹³CH₃OH. For each line we report wavelength, pump offset from the center of the exciting CO₂ line, relative polarization, optimum operating pressure and intensity. The LaseRitz program was able to assign one of the new laser systems of ¹²CH₃OH, involving two new far-infrared laser lines.PACS 42.55.Lt; 42.62.Fi     

R branch tuning characteristics of the13CH3F Raman FIR laser

Summary We described a¹³CH₃F Raman laser pumped by a grating tuned 20 atmospheres CO₂ laser. The emission characteristics of the¹³CH₃F laser extends from 14 cm^–1–35 cm^–1 and from 49 cm^–1–72 cm^–1; about 65% of these frequency ranges can be covered with tunable radiation. The characteristics shows a strong dependence on the rotaional quantum numbers of the states involved in the Raman laser transitions and, within each tuning interval, on the frequency offset with respect to the frequencies of resonant transitions. We obtained, at 51 cm^–1, a maximum FIR laser pulse energy of about 800 J (at a pump energy of 200 mJ), corresponding to a photon conversion of about 8%. In some cases we have observed simultaneous emission at a Raman and a cascade frequency. In addition, FIR emission power dependence on¹³CH₃F gas pressure and pump pulse power were investigated for different J quantum numbers.     

Optically-Pumped Far-Infrared Laser Lines of Methanol Isotopomers: 12CH3OH, 12CH3OD, and 12CH2DOH

Twenty-seven new far-infrared laser lines from the isotopomers of methanol: ¹²CD₃OH, ¹²CH₃OD, and ¹²CH₂DOH, were obtained by optically-pumping the molecules with an efficient cw CO₂ laser. The CO₂ laser provided pumping from regular, sequence, and hot-band CO₂ laser transitions. The 2-m long far-infrared cavity was a metal-dielectric waveguide closed by two, flat end mirrors. Several short-wavelength (below 100 m) lines were observed. The frequencies of 28 laser lines observed in this cavity (including new lines and already known lines) were measured with a fractional uncertainty limited by the fractional resetability of the far-infrared laser cavity, of 2 parts in 10⁷.     

Far-infrared laser-emission spectroscopy on ammonia isotopomers

In this paper we report the investigation of the isotopic ammonia gases¹⁴NH₃,¹⁴NH₂D,¹⁴NHD₂,¹⁵NH₃ and¹⁵ND₃ optically pumped by a continuously tunable 20 atm CO₂-laser. We found 267 far-infrared emission lines, produced by both inversion and Raman processes, in the frequency range from 15 cm^–1 to about 250 cm^–1. 200 of these were observed for the first time. We obtained far-infrared Raman tuning ranges exceeding 3 cm^–1, photon conversion coefficients up to 12% and maximum output energies of 0.9 mJ. Furthermore, the optimum gas pressure, the polarization and the transient behavior of optically pumped ammonia have been investigated.     

Investigation of 13CH3OH methanol: new laser lines and assignments

We have reinvestigated ¹³CH₃OH as a source of far-infrared (FIR) laser emission using a CO₂ laser as a pumping source. Thirty new FIR laser lines in the range 36.5 μm to 202.6 μm were observed and characterized. Five of them have wavelengths between 36.5 and 75 μm and have sufficient intensity to be used in LMR spectroscopy. Using Fourier-transform spectroscopic data in the infrared (IR) and FIR regions we have determined the assignment for 10 FIR laser transitions and predict nine frequencies for laser lines which have yet to be observed. Received: 17 July 2000 / Published online: 6 December 2000     

Methanol laser lines from torsionally excited co stretch states, and from OH-bend, CH3-rock, and CH3-deformation states

Using a quasi-CW CO₂ oscillator-amplifier combination with peak power 300 Watt, we have generated FIR laser emission in weak absorption bands of CH₃OH. 40 new lines are reported, and their wavelengths are measured with a relative accuracy of 5×10^–5. A total of 72 lines are assigned. 34 of these involve torsional n=1, 2, and 3 states of the CO stretch and the vibrational ground state. The remaining lines are associated with the CH₃-rock, OH-bend, and CH₃-deformation modes. The latter are located 1460 cm^–1 above the ground state, and are pumped by simultaneous vibrational excitation and torsional deexcitation.     

Measurement and assignment of new FIR laser lines in12CH3OH and13CH3OH

We have found twelve new FIR laser lines in¹²CH₃OH and thirty three in¹³CH₃OH. Both molecules were pumped by a regular cw CO₂ laser. We have also assigned 20¹³CH₃OH laser lines to specific rotational energy levels in the excited C-O stretchhindered rotation combined states     

Tuning characteristics of a high pressure CO2 laser pumped CH3F Raman laser

Conclusion We described a CH₃F Raman laser pumped by a two stage 20 atmospheres CO₂ laser. The emission spectrum of the CH₃F laser at 11 Torr extends from 23 cm^–1 to 45 cm^–1 when the CO₂ laser is scanned over the 9R emission branch at a fixed pump power of 180 mJ. The emission spectrum shows a strong structure with large parts where the FIR energy decreases to zero. This fact makes the use of such a laser for spectroscopic scanning experiments in the FIR difficult. The laser is, however, very suited for working at fixed but adjustable FIR frequencies. The pulse energy in the maxima of the emission characteristics at a pump energy of 180 mJ exceeds 300 J, which corresponds a photon conversion coefficient of more than 6%.     

Optically Pumped Far-Infrared Laser Lines of Methanol Isotopomers: 12CD3OH, 12CH3OD, and 12CH2DOH

Twenty-seven new FIR, far-infrared, laser lines from the isotopomers of methanol: ¹²CD₃OH, ¹²CH₃OD, and ¹²CH₂DOH, were obtained by optically pumping the molecules with an efficient cw CO₂ laser. The CO₂ laser provided pumping from regular, sequence, and hot-band CO₂ laser transitions. The 2 m long far-infrared cavity was a metal-dielectric waveguide closed by two, flat end mirrors. Several short-wavelength (below 100 m) lines were observed. The frequencies of 28 laser lines observed in this cavity (including new lines and already known lines) were measured with a fractional uncertainty limited by the fractional resetability of the far-infrared laser cavity, of 2 parts in 10⁷.     

Partly tunable mid-infrared NH3 laser

Using a continously tunable pulsed 20-atmosphere CO₂ laser as a pump source, we generated pulses of mid-infrared radiation, partly tunable in frequency intervals in the range between 200 and 900 cm^–1 via stimulated Raman scattering in gaseous ammonia. As a Raman cell we used a multiple pass cell. We observed for¹⁴NH₃ and¹⁵NH₃ laser lines at 52 different frequencies with 39 lines observed for the first time. Tuning ranges up to 150 GHz and peak powers of several MW were achieved. The quantum efficiency reached 40 %.     

Infrared spectra of CH3Br: The 2ν2 band near 2600 cm−1

The rotational fine structure of 2ν₂ has been studied under high resolution (0.03 cm^?1) for CH₃⁷⁹Br and CH₃⁸¹Br. About 700 lines have been assigned for each isotopic species. The band centers have been found at 2596.871 and 2596.815 cm^?1, respectively.     

A new efficient far-infrared optically pumped laser gas: CH3 18OH

The¹²CH₃ ¹⁸OH molecule has been investigated for new far-infrared laser lines by optically pumping it with a cw waveguide CO₂ laser. The larger tunability (318 MHz) with respect to a conventional CO₂ laser permits the pumping of many¹²CH₃ ¹⁸OH lines. As a consequence 100 new laser lines have been discovered, ranging from 34.6 m to 653.2 m in wavelength. The infrared spectrum of¹²CH₃ ¹⁸OH has been observed and all the fundamental vibration energies measured.     

Assignments of optically pumped CD3OH laser lines

Six FIR laser lines from CD₃OH pumped by the 10R(36) and the 10R(18) CO₂ laser lines are assigned to specific rotational energy levels in the excited C–0 stretch state. It is found that their upper laser levels are shifted by a Fermi resonance between the C–0 stretch vibration and the third and forth harmonics of the torsional mode. The Fermi resonance shifts are +0.332 cm^–1 and +2.251 cm^–1 for the upper laser levels pumped by the 10R(36) and the 10R(18) CO₂ laser lines, respectively. Calculated frequencies of the pump and the laser transitions agree with those of the pump CO₂ laser lines and the observed FIR laser lines within estimated accuracy.     

Infrared and far-infrared spectroscopy of CH3OH: TeraHertz laser lines and assignments

We use a ¹³CO₂ laser as optical pumping source to search for new THz laser lines generated from ¹³CH₃OH. Nineteen new THz laser lines (also identified as far-infrared, FIR) ranging from 42.3 μm (7.1 THz) to 717.7 μm (0.42 THz) are reported. They are characterized in wavelength, offset, relative polarization, relative intensity, and optimum working pressure. We have assigned eight laser lines to specific rotational energy levels in the excited state associated with the C-O stretching mode.     

Single line high efficiency tunable fir generation by resonant four-wave mixing in CH3 pumped by a multiatmosphere tunable CO2 laser

By pumping CH₃F with a high pressure tunable TE-CO₂ laser, the resonant four-wave mixing process (RFWM) generates a very efficient tunable single line FIR emission at the Raman frequency. This result is strictly related to the spectroscopic structure of the CH₃F molecule. By means of this process, a tunable FIR emission on a 0.1 cm^–1 bandwidth 150 kW (8 mJ) single line, is obtained which can be used for many FIR multiphoton applications.     

Efficient generation of FIR radiation by optical pumping of D2 18O

In this paper we show that D₂ ¹⁸O vapour, optically pumped with a continuously tunable high pressure CO₂ laser, is an excellent source for far infrared radiation. Both high photon conversion coefficients and broad Raman gain regions were found for a large number of new laser transitions spread over the frequency range from 25 cm^–1 to 240 cm^–1. We demonstrate that these Raman gain regions can be used to generate far infrared laser pulses with high intensity and durations of about 100 ps.     

Assignment of submillimeter laser lines in methyl chloride

Assignments are proposed here for 19 far infrared laser lines in CH₃Cl excited by a CO₂ laser and for the CH₃Cl transitions which are pumped. In each case the chlorine isotopic species involved is determined. In addition, a complete set of band parameters is obtained for the ν₆ band of CH₃³⁷Cl as well as for CH₃³⁵Cl. The vibrational isotopic shift Δν(35–37) is found to be 0.386 cm^?1 for the ν₆ band of CH₃Cl.     

Further investigations on ir pumping of CH3OD and CD3OD by a cw CO2 laser

Respectively, 41 and 36 new cw far-infrared lasing lines have been observed using a waveguide resonator in CH₃OD and CD₃OD pumped by a low-pressure CO₂ laser emitting in the 9.4, 10.4 m regular bands and in the 10.8 m hot band. The wavelength range was 46.6 m–1.67 mm in CH₃OD and 53.6 m–1 mm in CD₃OD.     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.