Far-infrared laser action in vinyl chloride, vinyl bromide, and vinyl fluoride optically pumped by a CW N2O laser

This paper reports the first use of a N₂O laser for optically pumping vinyl halides, to obtain new cw submillimeter laser lines. Eighteen far-infrared (FIR) emissions have been observed in vinyl chloride, twenty five in vinyl bromide and thirty eight in vinyl flouride.     

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.     

New cw FIR laser lines from optically pumped silyl fluoride (SiH3F)

FIR laser action has been observed for the first time in a molecule containing silicon: silyl fluoride, SiH₃F. Eleven new cw optically pumped lines between 187 and 1014m were detected from both open resonator and waveguide structures. Although the chlorine analogue, SiH₃Cl, showed strong absorption at every CO₂ laser frequency no FIR laser emission was detected at the pump powers available.     

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.     

A review of optically pumped far-infrared laser lines from methanol isotopes

The technique of optical pumping in polar molecules is the most efficient for Far-Infrared (FIR) laser generation, providing also a versatile and powerful tool for molecular spectroscopy in this spectral region. Methanol (CH₃OH) and its isotopic varieties are the best media for optically pumped FIR laser, with over thousand lines observed, and the most widely used for investigations and applications. In this sense, it is important organize and make available catalogues of FIR laser lines as complete as possible. Since the last critical reviews of 1984 [1] on methanol and its isotopic varieties [2,3,4], over hundred papers have been published dealing with hundreds of new FIR laser lines. In 1992 a review of FIR laser lines from CH₃OH was presented [5]. In this communication we extend this work to the other methanol isotopes, namely CH₃OD, CD₃OH, CD₃OD,¹³CH₃OH,¹³CD₃OH,¹³CD₃OD, CH₃ ¹⁸OH, CH₂DOH, CHD₂OH and CH₂DOD.Work supported by FAPESP, CNPq, FAEP-Brasil, and CNR-Italia     

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.     

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.     

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     

New Far-Infrared Laser Lines and Frequency Measurements of Acetaldehyde and Vinyl Fluoride

Eight far-infrared laser lines have been obtained by optically pumping acetaldehyde (CH₃CHO) and nine by pumping vinyl fluoride (CH₂CHF) with a cw CO₂ laser. The far-infrared laser structure used a metal-dielectric waveguide cavity. This is the first reported observation of four of the laser lines in acetaldehyde. In this work, we measure the frequency, optimum pressure of operation, relative intensity, relative polarization, and pump offset from CO₂ laser-line center.     

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.     

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.     

Predicted new optically pumped FIR molecular lasers

A total of nine cw FIR laser lines are reported from two new FIR laser molecules; CH₂CHF and S¹⁸O₂. These two are from a list of twelve candidate molecules that were predicted using a set of selection criteria. The candidate D₂ ¹⁸O was tested, but did not lase. Combining these results with independent studies on other candidates, brings the number of proven laser molecules to 4 out of 5 that were tested. These results confirm the value of the selection criteria as a guideline for predicting new optically pumped FIR laser molecules.Work supported by the Department of Energy     

Optical pumping by CO2 and N2O lasers: New cw FIR emissions in vinyl cyanide

A systematical study of optical pumping by CO₂ and N₂O lasers using a FIR metallic waveguide has been undertaken in vinyl cyanide. 97 new FIR laser lines are reported in the wavelength range 400 m–1,5 mm.Unité associée au CNRS (UA 836).     

Strong far-infrared laser action in carbonyl fluoride and vinyl fluoride

Intense far-infrared laser action is reported for carbonyl fluoride and vinyl fluoride. Eleven new lines with wavelengths between 339 m538 m were obtained by optically pumping carbonyl fluoride with numerous lines of the 10.4 m band of a cw CO₂ laser. Twenty-three lines with wavelengths in the range 172 m783 m were detected when pumping the recently discovered efficient FIR laser molecule vinyl fluoride. In addition, three very weak new lines were found using 1.1-difluoroethylen.     

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.     

Optically pumped far infrared lasers

The far-infrared (FIR) region of the electromagnetic spectrum is commonly thought of as the wavelength region ≈ 30μm-≈2 mm. Thus, the FIR wavelength region is located between the more familiar areas of microwaves and optics. Primarily due to the lack of FIR sources and detectors, the FIR region is difficult to access and therefore relatively unexplored and unused. The FIR source problem is presently under attack from neighbouring disciplines; from the microwave side by extending the frequency operating range of classical electron tube oscillators (e.g. backward wave oscillators) and semiconductor devices (e.g. IMPATT and quantum well oscillators) and from the optical side primarily by optically pumped molecular gas lasers.The FIR technology evolution accelerated in the mid 60's with the discovery of the discharge pumped hydrogen cyanide laser, lasing at a handful of lines located at about 330μm wavelength. However, the most important step towards a useful coherent FIR source was the discovery of the optically pumped FIR laser in 1970. In optically pumped FIR lasers a molecular gas (e.g. methyl fluoride methyl alcohol, formic acid) is pumped by an external laser, usually a carbon dioxide laser. The FIR laser transitions typically takes place between adjacent rotational levels in an excited vibrational state. Today, optically pumped FIR lasers cover the full FIR region by more than one thousand discrete laser lines observed in hundreds of FIR laser media. FIR output powers on the order of 1–100 mW are available from a vast number of laser transitions.Despite the rapid development of semiconductor FIR oscillators the optically pumped FIR laser is still the only practical unit that bridge the full frequency-gap between microwaves and optics. The fact that FIR lasers are considered as local oscillators in space born applications, indicate that FIR laser technology has matured considerably.This survey paper discusses optically pumped FIR lasers from the engineer's point of view: principles of operation, design and characteristics.     

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.     

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 for optically pumped CD3OH

Twenty new cw FIR laser lines in CD₃OH, optically pumped by a CO₂ laser, are reported. The frequencies of 39 of the stronger laser lines were measured relative to stabilized CO₂ lasers with a fractional uncertainty, as determined by the reproducibility of the FIR frequency itself, of 2 parts in 10⁷.Contribution of the U.S. Government, not subject to copyright.     

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.