Oversized helical waveguides for optically pumped far-infrared lasers

The feasibility and the theory of oversized helical waveguides for optically pumped far-infrared lasers are studied. The dispersion relation and the relevant pass bands are shown.     

Polarization characteristics in optically pumped,far-infrared rectangular waveguide lasers

It has been shown that a linearly polarized, comparatively strong output power can be obtained from optically pumped, far-infrared rectangular waveguide lasers when the rectangular, metallic oversized waveguide is used as a tall guide instead of a standard guide.     

Pump beam propagation in circular waveguides of optically pumped far-infrared lasers

A theory is presented describing the infrared pump beam propagation in circular waveguides of OPFIRLs. Based upon a ray representation of the Gaussian beam, the overall transport of pump power into the gas by nonlinear absorption and into the wall of the waveguide by partial reflections can be balanced. The theory was used to study the typical pumping conditions in OPFIRL and the main results are presented.     

Application of the optoacoustic effect in optically pumped submillimeter lasers

The dependence of the optoacoustic signal generated in an optically pumped submillimetre laser system on gas pressure and modulation frequency has been studied experimentally and the results accounted for theoretically. With care an extracavity optoacoustic cell containing the laser gas diluted with air can be used to stablize the pump laser frequency to maximum absorption but this does not always optimise laser output.     

High power,high efficiency optically pumped NH3 lasers

A simple and efficient NH₃ laser was tuned over more than 70 vibrational band transitions between 10.08 and 14.14 m. The active medium was a dilute mixture of ammonia in argon and was optically pumped by the 9R(30) transition of a pulsed TEA-CO₂ laser. Output energies greater than 1 J per pulse were observed on several of the strongest lines. In a non-selective cavity an energy conversion efficiency of greater than 35% was obtained with a maximum output energy of 4.6J. Optically pumped NH₃ is shown to be a flexible and efficient system for the downconversion of CO₂ radiation.     

On the pulse width of synchronously pumped lasers

The pulse width of a synchronously pumped laser chiefly depends on the available cavity bandwidth and the pump-pulse duration. A functional form of this dependence was suggested in the literature. We present an alternate relation which is supported by analytical and numerical results, as well as by experimental results, obtained by us and by others.     

Frequencies of some optically pumped submillimetre laser lines

Precise frequencies of far infrared (FIR-) laser lines of HCOOH, CH₃OH, CH₃I, CH₃F have been measured by comparison with harmonics of frequency-locked mm-wave klystrons.     

Experimental investigation of the MIR optically pumped ammonia bidirectional ring laser

We have studied the Doppler-broadened 11.76 m ¹⁵NH₃ emission line optically pumped in a ring resonator by a cw CO₂ laser operating on the 10R(42) line. In the pure ammonia, even if the pumping occurs inside the Doppler width, the two-photon Raman process seems to be responsible for the laser emission. Both in the pure ¹⁵NH₃ and in the ¹⁵NH₃, N₂, and He mixture we demonstrate the possibility of obtaining a unidirectional laser amplifier.This work has been supported by Direction des Recherches Etudes et Techniques under contract No. 87/222     

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.     

Systematic evaluation and prediction of the pulse width of synchronously pumped lasers

Received: 17 March 1997/Revised version: 21 July 1997     

Three-photon contributions in optically pumped lasers

A signal flow graph representation of the density matrix equations appropriate to a serial three-wave interaction is introduced, from which perturbation theory and AC Stark shift information may be extracted. The conditions for a large interaction cross section for the three-photon transition are deduced and applied to selected experimental situations with the main conclusion being that the effect may be present in a large number of CW and pulsed experiments.Work supported by the Army Research Office, National Science Foundation, and the Joint Services Electronics Program.Also with the Coordinated Science Laboratory.     

Improving the efficiency of certain optically pumped lasers

It is shown that for certain optically excited symmetric top molecules which lase in the far-infrared that it is possible to increase their lasing efficiency through resonant pumping of the higher k quantum number transitions which have increased statistical weights due to increased molecular symmetry.     

Tunable far-infrared radiation from optically pumped potassium Rydberg transitions

We report the generation of tunable far-infrared radiation by the optical pumping of potassium metal vapor to the13p Rykberg state. Subsequent cascade by stimulated emission is measured at several wavelengths between 76 and 146 cm^–1 with a conversion quantum efficiency of greater than 10 percent. Emission observed in this region are tuned up to 18 GHz by the application of a pulsed Stark field across a parallel-plate heat pipe. Cascade branching to the 11d to 10f transition at 146 cm^–1 is observed which can be tuned up to 7 cm^–1 in our device. Similar branching following excitation up to the 18 p state is shown to provide almost complete tunability in the far-infrared region.Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

Threshold singularities of optically pumped dye lasers

A complete theoretical model for optically pumped dye lasers is studied using the rate equation approach which includes excited singlet and triplet state absorption effects. Closed-form solutions under steady-state conditions reveal a novel nonlinear threshold phenomenon: partial reabsorption of the excited laser light can lead to a discontinuous onset of laser oscillation above laser threshold. Theoretical and experimental results for a transversely and longitudinally pumped rhodamine 6G laser are presented in terms of softmode and hardmode behavior at threshold.     

Pulse formation in synchronously pumped infrared dye lasers

Pulse formation in synchronously pumped dye lasers with fast relaxing dyes is treated by computer simulation. The influence of spontaneous emission and chirp, as well as cavity mismatch, on the pulse characteristics and stability of generation are discussed.     

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     

Infrared recombination lasers pumped by low energy Nd: YAG and excimer lasers

24 infrared laser lines on atomic and ionic transitions have been observed in recombining plasmas by vaporizing and ionizing Cd, Pb, Sn, Zn, and Mg with low energy Nd:YAG or excimer pump-lasers. For operation and optimization of the recombination lasers separated plasma spots and a plasma confinement have been used. The operation of shorter wavelength systems by isoelectronic scaling is discussed.     

Laser frequency measurements and spectroscopic assignments of optically pumped 13CH3OH

A three-laser heterodyne system was used to measure the frequencies of twelve optically pumped laser emissions from ¹³CH₃OH in the far-infrared (FIR) region. These emissions, ranging from 54 to 142 μm, are reported with fractional uncertainties up to ±2×10^-7 along with their polarization relative to the CO₂ pump. Using the 9P32 and 10R14 CO₂ lines, complete spectroscopic assignments for two laser systems were confirmed. Received: 31 May 2001 / Published online: 19 September 2001     

A theoretical investigation of wedged capacitive strip-grating output couplers for optically pumped terahertz lasers

The output power for terahertz lasers influenced drastically by slight changes in the transmittance of the output coupler for a certain terahertz frequency has been discussed in the paper. Therefore it is necessary to design an output coupler whose transmittance does not rapidly modulate with frequency. To obtain the flat and accurate transmittance spectrum in a narrow wavenumber interval (say 3 cm⁻¹), a wedged output coupler is proposed. This conclusion has been revealed after analyzing the disadvantages of two types of capacitive strip-grating output couplers, and theoretically studying its transmission properties. The theoretical results show that the coupler can not only provide flat and accurate transmittance spectrum and thus effectively suppress the etalon effects occurring frequently in previous experiments but also thoroughly eliminate the transmittance sensitivity to the slight shift of substrate thickness. Moreover, the wedged substrate of the improved output coupler can be used repeatedly in the process of adjusting the strip-grating parameters to meet various transmittance requirements for optically pumped terahertz lasers.