Far-infrared laser stark spectroscopy of CH3OH and13CH3OH

The high resolution laser Stark spectra of methanol and¹³C-substituted methanol have been studied up to Stark fields of about 60 000V/cm with the HCN and DCN lasers. Numerous families of absorption lines have been observed in both parallel and perpendicular polarizations. For methanol, the transitions J _k =7₅ 6₄ A, _t=0; J _k =11₄ 10₃ E _l , _t=0; and J _k =17₃ 16₂ E₂, _t=0 have been identified while the assignments for¹³C-substituted methanol are J _k =14₈ 15₇ A, _t=0; J _k =15₃ 14₂ A⁺, _t=0; J _k =10₇ 9₆ A, _t=0; and J _k =27₉ 27₈ E₁, _t=0. Zero-field frequencies for the assigned transitions are given with improved accuracy over those calculated from available molecular constants, especially for¹³CH₃OH.     

Far infrared laser lines and assignments of CH3OH: a review

Methyl alcohol is the most important lasing molecule in the Far-Infrared (FIR) spectral region, and the most widely used for investigation and for applications. Since the last critical review of 1984, over seventy papers have been published dealing with the FIR laser lines and the infrared spectroscopy of CH₃OH. In 1984 we could list about 330 FIR laser lines, 98 of which were measured in frequency and 105 assigned. Since then more than 70 papers were published increasing the number of the known laser lines to 575 (103 measured in frequency). Also the FIR and IR spectroscopy was largely improved thanks to the analysis of high resolution FT spectra, and the number of the correctly assigned laser lines has been increased to 224. The wavenumbers of the assigned lines can now be predicted with an accuracy of about 0.001 cm^–1 or better, thus approaching the accuracy of the experimental frequency measurements.     

Wavelengths for new CH3OH laser lines

Using a grating-tuned CO₂-TEA laser to pump CH₃OH in a metallic-wave-guide resonator, submillimeter laser emissions have been produced by pumping with 36 lines in the 9.4m CO₂ band and with 23 lines in the 10.6m band. Several dozen new SMM laser lines were observed. Wavelengths accurate to within 0.1% are given for 12 previously unmeasured lines between 34m and 225m.     

Experimental study on miniature pulsed CH3OH far-infrared laser

Using a grating tuned TEA-CO₂ laser with 9P(16) line to pump a 10cm or 20cm long miniature Fabry-Perot cavity CH₃OH laser, pulsed far infrared(FIR) lines of 570.6um and 918um wavelengths were observed, the latter is a new line. Operation performance and spectral characteristics of the miniature CH₃OH laser were studied. The project was supported by the Special Research Foundation of Doctorate Station in University of P.R.C.     

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.     

Frequency measurements of far infrared12CH3OH laser lines

We have measured the frequencies of 12 known and 3 new submillimeter laser lines obtained by pumping¹²CH₃OH with a cw waveguide CO₂ laser in a Fabry-Perot far infrared resonator. We have also measured the relative polarization and the pumping CO₂ frequency offset for each line.Supported in part by a joint grant with the U.S. National Science Foundation # INT80-19014 and the Brazilian Conselho Nacional de Pesquisas (CNPq).Work of the U.S. Government; not subject to U.S. copyright.     

Hyperfine structure of CH3OH

Hyperfine structure of the (0, 0, 1) - (1, 0, 1) transition of methanol has been investigated by beam absorption and of the (J, 1, 3?) → (J, 1, 3+) transitions for J = 2, 3, and 6 by beam-maser spectroscopy. The best-fit results for the spin-rotation and spin-spin coupling constants $\text{C}{}_{\mathrm{JK\tau \pm }}{}^{\mathrm{(i)}}$ and $\text{D}{}_{\mathrm{JK\tau \pm }}{}^{\mathrm{(i)}}$, respectively, are in kHz¹: $\text{C}{}_{101}{}^{\mathrm{(1)}}\text{= 2.4(10)}$, $\text{C}{}_{101}{}^{\mathrm{(2)}}\text{= ?0.6(10)}$, $\text{D}{}_{101}{}^{\mathrm{(1)}}\text{= ?13.8(9)}$, $\text{D}{}_{101}{}^{\mathrm{(2)}}\text{= 7.0(9)}$, $\text{C}{}_{\mathrm{213?}}{}^{\mathrm{(1)}}\text{= ?5.0(10)}$, $\text{C}{}_{\mathrm{213?}}{}^{\mathrm{(2)}}\text{= ?5.5(10)}$ and ($\text{C}{}_{\mathrm{J13?}}{}^{\mathrm{(2)}}\text{- C}{}_{\mathrm{J13+}}{}^{\mathrm{(2)}}\text{) = 0.98(9)}$.     

Anisotropic unidirectional operation of an optically-pumped CH3OH ring laser

We report directional anisotropy of the outputs of an optically pumped far-infrared ring laser, which operates on the 119 μm line of CH₃OH, with special emphasis on the effect of the Raman-type two-photon process on the unidirectional operation. By use of a Doppler broadened three-level system which allows the coexistence of two counterpropagating far infrared (fir) fields as well as a pump field in the cavity, an expression for the fir intensity determining equations is derived. A numerical calculation has been carried out to map the threshold contours on the parameter plane spanned by the cavity and pump detuning frequencies. The output directionality is shown to be a direct consequence of the gain anisotropy due to the two-photon process. Furthermore, it is also noted how the dynamic Stark effect modifies the threshold contours of the forward output.     

Operating parameter optimization of optically pumped CH3OH far-infrared laser

By solving the density matrix equations of a quantum system, the output power intensity of an optically pumped CH₃OH FIR laser (CH₃OH-OPFIRL) was calculated by means of iteration method, and the spectral characteristics were got. Base on the calculation, optimization of operating parameters including operating gas pressure, pumped power and output coupling coefficient of the CH₃OH cavity laser were systematically studied. Experimental, a series of FIR emissions of the CH₃OH cavity laser pumped by TEA-CO₂ laser with 9P(16) line were measured. The experimental results were in good agreement with theoretical calculations. The project was supported by the Special Research Foundation of Doctorate Station in University of P.R.C.     

A twin optically-pumped far-infrared CH3OH laser for plasma diagnostics

A twin optically-pumped far-infrared CH₃OH laser has been constructed for use in plasma diagnostics. The antisymmetric doublet due to the Raman-type resonant two-photon transition is reproducibly observed at 118.8 m. With the 118.8-m line, it is obtained from the frequency separation of the anti-symmetric doublet that CH₃OH absorption line center is 16±1 MHz higher than the pump 9.7-m P(36) CO₂ laser line center. It is shown that the Raman-type resonant two-photon transition is useful in order to get several-MHz phase modulation for the far-infrared laser interferometer. Some preliminary performances of this twin laser for the modulated interferometer are described.This work was carried out under the collaborating research program at the Institute of Plasma Physics, Nagoya University, Nagoya 464, Japan.     

High power, long pulse, CH3I far infra-red laser

A high power, far infra-red laser, pumped by a long pulse high energy CO₂ laser, has been developed to produce 8 μs pulses at 447 μm. The influence of the molecular weight of the far infra-red gas on the absorption of the pump energy is discussed. The results show that the heavy molecules are most convenient for long pulse far infra-red lasers.     

Frequency measurements of 3 to 11 THz laser lines of CH3OH

We measured the frequencies of 12 far-infrared laser lines generated in a high- frequency Fabry-Perot laser cavity containing methanol, pumped by a CO₂ laser. The frequencies are in the range 2.8 to 11.4 THz (105.4 to 26.2 µm). Ten of the measured frequencies are higher than 7 THz, and help to fill the laser frequency gaps in this region. Five of the measured lines are new. The 11.4 THz line has the highest frequency of an optically pumped laser ever measured with the CO₂ laser heterodyne technique.This work has been financed by the Brazilian Government - Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and by the United States Government - NASA Grant W-18, 623.Contribution of NIST, not subject to U.S. Copyright.     

A high power CH3OH FIR laser system with long-term stability

A CH₃OH FIR system has been developed for plasma diagnostics. A CO₂ laser devoted to pump the CH₃OH molecule has been studied. Different internal diameters of FIR cavity, input coupling holes and focusing lenses have been experimented.It has been found that the system formed by three subsystems-pump laser, guiding channel and FIR cavity-behaves like an unique system. A long term stability has been reached with a proper system design.Work supported by ENEA contract No. C/451 (Dipart. Fusione, Associazione Euratom-Enea, CRE Frascati, C.P. 65, 00044 Frascati, Italy).Student     

Optical-optical double resonance spectra of CH3OH

An acousto-optic modulator driven at a radio frequency, $\text{Ω}{}_{\mathrm{RF}}$, was used to modulate a cw single-mode laser, frequency $\text{Ω}{}_{\mathrm{L}}$, producing a single sideband at $\text{Ω}{}_{\mathrm{L}}\text{+ Ω}{}_{\mathrm{RF}}$. This system has been used to observe optical-optical double-resonance signals in CH₃OH using both normal and isotopically labeled CO₂ lasers. The positions of the double-resonance signals depend only on $\text{Ω}{}_{\mathrm{RF}}$. The OODR signals have been used to assign several vibration-rotation-torsional transitions which correspond to near coincidences with CO₂ laser lines. The results have been used to assign and predict optically pumped laser lines, and to measure the electric dipole moment in vibrationally and torsionally excited states.     

Microwave and submillimeter-wave spectra of CH3OH

Frequency measurements and assignments have been made for CH₃OH lines in the 15- to 400-GHz region. The a-type R-branch multiplets are reported up to J = 8 ← 7 for the v_t=0 torsional ground state, and to J = 6 ← 5 for the v_t=1 and v_t=2 excited states. Several new Q branches are listed and many b-type P- and R-branch transitions have been identified over a wide range of J and k values.     

New laser lines from optically pumped CH3OH: measurements and assignments

New CW FIR laser lines from optically pumped CH₃OH are reported. Experimental values for wavelength, polarization and pump offsets are given. Lines assignments are proposed. New experimental results and possible assignments are also given for previously reported lines.     

A magneto-optically modulated CH3OH laser for Faraday rotation measurements in Tokamaks

Distortion-free intracavity polarization modulation of an optically pumped CH₃OH laser is shown to be viable. The possible use of this modulation technique to make a multichannel Faraday rotation measurement on a Tokamak device is discussed. In addition, the CdTe Faraday modulator employed in this study is shown to have an anomalously large Verdet constant.     

K-shell excitation of CH4, NH3, H2O,CH3OH,CH3OCH3 and CH3NH2 by 2.5 keV electron impact

The regions around the respective carbon, nitrogen and oxygen K-edges of CH₄, NH₃, H₂O, CH₃OH, CH₃OCH₃ and CH₃NH₂ have been investigated by electron energy loss spectroscopy using a beam of 2.5 keV electrons. All spectra show a number of discrete peaks just below the K-shell ionization threshold. These discrete structures have been interpreted as being associated with the promotion of a K-shell electron to Rydberg orbitals which converge to the K-shell ionization threshold.     

Force field variations along the torsional coordinates of CH3OH and CH3CHO

We examine the question of reduced Hamiltonians for the torsion-rotation problem and in particular the question of the continuity of frequencies obtained by projecting out a large-amplitude torsional coordinate. We find that suitable results for torsion-rotation analysis can be obtained using either a rectilinear or a curvilinear formalism.