New FIR laser lines from hydrazine and assignments

Our new waveguide pulsed CO₂ laser, with peak powers above 1 kW, has allowed us to observe 24 new far-infrared laser lines emitted by hydrazine. Each of them is characterized in wavelength, relative polarization, intensity, optimum operating pressure and pump offset from the center of the exciting CO₂ line. These new laser emissions either form pairs sharing the same pump line, or complete such pairs with lines known from the literature. In the latter case, we have measured the relative polarization and offset of the partner lines whenever they were not reported in the literature. The availability of laser systems with two emission lines orthogonally polarized and sharing the same upper level is expected to facilitate the assignment work. We present complete assignments for four FIR laser emissions, and we propose J and K values for 12 further laser systems. PACS 42.55.Lt; 42.62.Fi     

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 an optically pumped far-infrared laser with isotopic 13C16O2 pumping

A ¹³C¹⁶O₂ laser optically pumping a FIR laser has resulted in 17 new FIR cw emissions from 78.5 μm to 917 μm. The FIR media were: CD₃OD, CH₃OD, CD₃OH, NH₃ and ¹⁵NH₃. Interesting effects have been observed with a combination of NH₃ and CD₃OD resulting in a new FIR emission. Two new FIR emissions at 181.5 μm and 355.5 μm have been observed with a ¹²C¹⁶O₂ laser optically pumping CD₃OD.     

Discovery and frequency measurement of short-wavelength far-infrared laser emissions from optically pumped <Superscript>13</Superscript>CD<Subscript>3</Subscript>OH and CHD<Subscript>2</Subscript>OH

A three-laser heterodyne system was used to measure the frequencies of twelve previously observed far-infrared laser emissions from the partially deuterated methanol isotopologues ¹³CD₃OH and CHD₂OH. Two laser emissions, a 53.773 μm line from ¹³CD₃OH and a 74.939 μm line from CHD₂OH, have also been discovered and frequency measured. The CO₂ pump laser offset frequency was measured with respect to its center frequency for twenty-four FIR laser emissions from CH₃OH, ¹³CD₃OH and CHD₂OH. PACS 07.57.Hm; 42.55.Lt; 42.62.Eh     

FIR laser assignments and frequency predictions for optically pumped13CD3OH by high-resolution Fourier transform spectroscopy

Continued study of the high-resolution Fourier transform spectroscopy (FTS) of the fundamental CO-stretching band of¹³CD₃OH has given additional insight into the far-infrared (FIR) laser emission observed when this molecule is optically pumped by a CO₂ laser. Eleven IR-pump/FIR-laser transition systems are considered. Seven represent completely new assignments, while four have been presented previously but are discussed further with reference to recently reported experimental data. Ten of the assignment schemes have been rigorously checked by forming closed combination loops, and accurate FIR laser wavenumbers have been obtained. The superiority in precision of the FIR laser wavenumbers determined from FTS combination loops over those from traditional wavelength measurements is demonstrated.     

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.     

Discovery and frequency measurement of far-infrared laser emissions generated by optically pumped CH2DOH

A recently improved three-laser heterodyne system was used to frequency measure ten previously observed optically pumped far-infrared (FIR) laser emissions from the partially deuterated methanol isotopologue CH₂DOH. Also, a 64.0 μm FIR emission generated by the 9P32 line of the carbon dioxide (CO₂) laser was discovered and frequency measured. These newly measured frequencies have fractional uncertainties on the order of ±2×10^-7 and correspond to laser wavelengths ranging from 42.6 to 152.7 μm. The offset frequency for the CO₂ pump laser was measured for twenty-two CH₂DOH FIR laser emissions. PACS 07.57.Hm; 42.55Lt; 42.62.Eh     

Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.     

New large offset far-infrared laser lines from CD3OH

The CD₃OH molecule has been investigated for new far-infrared laser lines by optically pumping with a cw waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser permits to pump many new CD₃OH lines. As a consequence 108 new laser lines have been discovered, ranging from 42.9 to 1155 m in wavelength. On some lines the effect of an electric Stark field has been investigated demonstrating a laser frequency tuning. The total number of known FIR laser lines from CD₃OH is increased to about 340 making this molecule the most prolific together with CH₃OH.     

Reinvestigation of far-infrared laser emissions from hydrazine and deuterated isotopes of difluoromethane and methanol

Hydrazine (N₂H₄) and the deuterated isotopes of difluoromethane (CD₂F₂) and methanol (CH₃OD and CD₃OH) have been reinvestigated as sources of far-infrared (FIR) laser emissions using an optically pumped molecular laser system designed for wavelengths below 150 microns. With this system, seven FIR laser emissions from optically pumped N₂H₄, CH₃OD and CD₃OH were discovered with wavelengths ranging from 54.0 to 185.0 m. In addition, the polarizations of eight previously observed laser emissions from optically pumped N₂H₄, CH₃OD and CD₂F₂ were measured for the first time. All laser emissions are reported with their operating pressures, relative polarizations and wavelengths, measured to ±0.5 m. The effectiveness of this particular system in generating short-wavelength laser emissions has been further demonstrated by the improvement in output power observed from nine known FIR laser emissions. PACS 07.57.Hm; 42.55.Lt     

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.     

New phenomena related to pulsed far-infrared superradiant and Raman emissions

We report on new effects in relation to optical pumping of far-infrared (FIR) superradiance and Raman emissions in CH₃F, CH₃CN, D₂O, NH₃ by rapidly truncated 10 μm CO₂ laser pulses and optical-free-induction decay (OFID) 30 ps-10μm-CO₂ laser pulses. Thus, we have found a drastic reduction of the FIR-pulse duration which is closely related to the fast truncation of about 10 ps of the plasma shutter used in our OFID 10 μm-CO₂ laser system. The forward emissions exhibit the on-set of swept-gain superradiance and the appearance of Raman emission with increasing pressure in the FIR cell. This implies line competition between the superradiant and Raman emissions and thus results in different emission regimes which we have investigated systematically. The backward emissions are superradiant over the whole range of our investigations and show high quality with respect to stability and reproducibility which is important for applications.Furthermore, we have found that the CO₂-pump radiation and the generated FIR Raman emission interact mutually which results in anticorrelated fluctuations of the two fields. We have been able to interpret this effect as a result of periodic back-and-forth fluctuations of the Λ-like three-level molecular systems.Finally, we have observed the development of OFID of the truncated CO₂-pump pulses in the FIR-laser gases. This effect has been thoroughly investigated and as a result we have generated for the first time ps-10 μm-CO₂-OFID pulses with FIR-laser gases as spectral filters instead of the usual hot CO₂ gas. New phenomena and advantages of our new OFID system based on FIR laser gases are discussed.     

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.     

Short-wavelength far-infrared laser cavity yielding new laser emissions in CD3OH

A significantly improved far-infrared laser has been used to generate optically pumped laser emissions from 26 to 150 μm for CD₃OH. Using an X–V-pumping geometry, several new laser emissions have been found for CD₃OH. In addition, an increase in power, by factors from 10 to 1000, for many of the previously known shorter-wavelength laser lines, below 100 μm, has been observed. Frequency measurements for several lines have also been performed and have been reported to a fractional uncertainty up to ±2×10^-7, permitting the spectroscopic assignment of the laser transition. One of the frequency-measured lines, 44.256 μm observed using the 10R34 pump, has confirmed the assignment of the previously reported FIR emission (n,K;J)=(1,7;20)?(0,8;20)A in the ground vibrational state. Received: 26 October 2000 / Published online: 7 February 2001     

Far-Infrared Laser Assignments for Methylamine

Reported far-infrared laser lines for five different transition systems of CH₃NH₂ optically pumped by a CO₂ laser have been identified spectroscopically through a high-resolution Fourier transform infrared study of the C-N stretching band together with CO₂-laser/microwave-sideband broad-scan and Lamb-dip measurements. From the infrared analysis plus previous far-infrared (FIR) results for the ground vibrational state, quantum numbers have been assigned for seven methylamine FIR laser transitions and their C-N stretching pump absorptions coincident with the CO₂ laser lines. The assignments are confirmed through the use of closed frequency combination loops that also provide improved FIR laser frequencies to spectroscopic accuracy.     

13CD3OH and12CD3OH optically pumped by a13CO2 laser: Observations and assignments of FIR laser lines

In this work we report the first observation of FIR laser lines from¹³CD₃OH pumped by the¹³CO₂ isotope laser. Using the same pump we have also found 3 new lines from¹²CD₃OH. Tentative assignments for the absorption and emission transitions of the observed lines are also proposed.Work supported by FAPESP. CNPq, FAEP/UNICAMP-Brasil and NSF-USA     

Further new CW FIR lasting investigations in CH3I,13CH3I and CD3I: New lines and assignments

Forty seven new CW FIR emissions lines have been observed in CH₃I,¹³CH₃I and CD₃I, optically pumped by a CO₂ laser and a N₂ laser, in a metallic waveguide resonator. Assignments are given for a large number of these new lines.     

Electric field effects on an optically-pumped HCOOH FIR laser and Zeeman laser theory

Electric field effects have been investigated on the output power of six far-infrared (FIR) laser lines from H¹²COOH optically-pumped by a CO₂ laser with its polarization arranged perpendicular to the Stark field. Optoacoustic signals observed on the pump lines were hardly affected by the applied electric field up to 0.6 kV/cm. By neglecting the electric field effects on the pump transitions, Zeeman laser theory has been applied to the FIR laser transitions. Numerical calculation predicts the observed FIR output power as a function of electric field. Experessions for oscillation frequency and intensity in homogeneous limit are given, which may be applicable to any FIR Stark laser so far as the pump transition is free from electric field effects.     

New FIR lasers from CO2 laser-excited 1,1-difluoroethene

Forty two new far-infrared laser lines have been obtained from CH₂CF₂ by pumping with a 60 W CO₂ laser. Several of these emissions have been assigned to rotation transitions within the v4 and v9 vibration manifolds; hot and combination band transitions are suspected for the others.this work was funded by the Ministry of Defence