Simulation of parametric oscillation in the submillimeter range at pumping of the ZnGeP2 crystal by a train of 100-ps high-power pulses

Analysis is given for a possibility of singly resonant parametric oscillation in the submillimeter range at synchronous pumping of the ZnGeP₂ crystal by a train of 100-ps second-harmonic pulses from the CO₂ laser with the radiation energy 1.0 J. The calculation shows that using the ZnGeP₂ crystal and the second harmonic of the CO₂ laser with the energy density 1.8 J cm⁻², one can get the peak submillimeter radiation power from 3.6 to 12 MW in the range from 95 to 300 μm (1.0–3.3 THz). The expected peak power values are larger than the experimental ones obtained by other nonlinear optics methods.     

Amplification and saturation in a CO2 waveguide amplifier

An ir CO₂, dc current pumped, optical waveguide (WG) amplifier has been built, and its active medium optical parameters measured for several CO₂ emission lines, and their dependence from active medium total pressure, discharge current and temperature was investigated.High gain is found which, coupled with relatively high saturation power in the WG fundamental mode and ease of fabrication with this technology in long (up to 1.5 m) lengths, indicates promising use to efficiently amplify high spectral and spatial purity output of a short, highly tunable WG laser up to power levels suited for nonlinear spectroscopy and optical pumping. The dependence of the small signal gain coefficient and of the saturation parameter for individual rotational lines on the radiation intensity was computed using experimentally known parameters of the discharge plasma. The computation was carried out using the two mode rate equation approach for CO₂–N₂–He gas mixtures. A satisfactory agreement between theoretical and experimental results was obtained.Work supported by G.N.S.M.-C.N.R. and M.P.I.     

Optically pumped high-pressure DF-CO2 transfer laser

Pulsed sealed off CO₂ laser operation at 19 atm gas pressure has been demonstrated by pumping DF/CO₂/He mixtures with radiation from a pulsed DF laser. DF acts as an absorber for the pumping radiation, and the CO₂ upper laser level is populated via subsequent energy transfer. CO₂ pulse energy at 19 atm was 0.5 mJ corresponding to a photon conversion efficiency of 4% measured relative to the number of absorbed pumping photons.     

Substance separation by the action of a pulsed ir laser radiation on gas-mixture flows through capillaries

New aspects of substance separation by the laser driven diffusion of gaseous mixtures through capillaries are presented. By using the chopped radiation of a low power CO₂ laser, the experimental dependence of the separation coefficient on the pulse frequency in mixtures containing resonant and non-resonant gases was investigated. The induced effects agree with a model in which the number density of adsorbed molecules should be connected to temporal characteristics of the radiation. By avoiding heating effects, a pulsed laser irradiation may provide a new approach related to the practical purposes of substance separation in metal capillaries.     

Intense laser generation from an atomic-fluorine laser

An intensive generation of radiation from a discharge-pumped atomic-fluorine gas laser is reported. A peak power exceeding 330 kW and a total energy of more than 2 mJ is obtained for a number of lines in the red, using a NF₃He (1100) gas mixture at total pressure of 500 Torr. The circuitry optimization is described and the conditions for effective operation of the atomic-fluorine laser are discussed. The temporal and the spectral characteristics of the laser emission are also presented.     

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     

Efficient and widely step-tunable terahertz generation with a dual-wavelength CO<Subscript>2</Subscript> laser

Coherent terahertz radiation in a widely step-tunable range of 72.3–2706 μm (0.11–4.15 THz) has been generated in GaAs crystal by difference-frequency generation using one CO₂ laser with dual-wavelength output. The peak power of THz pulse reaches 35 W at the wavelength of 236.3 μm, which corresponds to a pulse energy of 2.1 μJ. An average power of 10 μW has been achieved when working repetitively. This efficient terahertz radiation source is more compact and widely tunable than other THz sources pumped by CO₂ laser.     

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%.     

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.     

Effective nonchain HF laser excited by a self-sustained discharge

Lasing and discharge in mixtures of SF₆ with hydrogen and hydrocarbons are investigated. If the chemical reaction is initiated by a self-sustained discharge (a generator with both an inductive and capacitive energy storage can be used), the maximum lasing efficiency is attained at high values of the ratio E/p (where E is the electric field intensity and p is the pressure in the mixture) if shaped electrodes and preionization of the discharge gap are employed. For the first time, the lasing efficiency obtained in a nonchain HF laser is as high as 10% of the energy deposit and 4.5% of the stored energy for a specific radiation energy of ≈140 J/(l atm). At high efficiencies, the emission spectrum of the nonchain HF laser significantly broadens and cascade lasing at P(3-2) → P(2-1) → P(1-0) vibrational transitions for several rotational lines is realized.     

Key methods for intensifying soft X-ray emission from a laser plasma for lithography

A two-pulse two-wave (Nd and CO₂ lasers) scheme is proposed for irradiating a laser target, which ensures the highest factor of laser radiation conversion to the X-ray range (13.5 nm ± 1%). Analytic estimates are obtained for parameters of pulses and of the target made of Xe or Li. Numerical optimization is performed for X-ray emission from a spherical Xe target exposed to a CO₂ laser pulse. The maximal factor of conversion of laser radiation to X rays is ～1%. Angular and spectral characteristics of X-ray radiation are obtained. The flux of fast Xe ions ejected from the target and damaging the Mo/Si coating of X-ray mirrors is estimated.     

Interferometric determination of the dispersion of vibrational polarizability and the integrated intensities of fundamental bands of 32, 34SF6 and NF3 molecules

The refractivity of gaseous SF₆ and NH₃ in the region of the intense absorption bands of these compounds was measured by two-beam, two-color interferometry using a He-Ne laser and a CO₂ laser tunable throughout its emission lines. Quantitative data on the profiles of the absorption bands of these gases were also obtained by IR Fourier spectroscopy. By using the joint processing of the results of refractometric and spectral measurements on the basis of the Kramers-Krönig formalism, the dispersion dependences of the vibrational polarizabilities of the given molecules were calculated and the integrated intensities of their fundamental vibrational bands were refined. A table of values of total and vibrational polarizabilities at the emission frequencies of the CO₂ laser was compiled.     

CO<Subscript>2</Subscript> laser oscillating in the range of 16 μm

The ability of a CO₂ laser to oscillate in the range of 16 (14) μm at room temperature was investigated experimentally and theoretically. The output energy per pulse was ~60 mJ at peak power of ~50 kW. It was necessary to minimize not only harmful losses but also useful ones in both channels 00⁰1–02⁰0 and 02⁰0–0110 and to increase the input energy, i.e., the density of free electrons in the discharge, in order to increase the peak power and energy of 16-μm radiation. The highest values of peak power and energy of radiation were reached at different pressures of the active mixture. The rotational bottleneck effect limiting the peak power and energy of oscillation was important at rather low pressures of the active medium. Oscillation at the R12 line is more preferable than that at the P12 line for use as 9.6-μm dumping radiation.     

A Broadband Infrared Laser Source (2.5–17 μm) for Plasma Diagnostics

This paper presents the results of studies aimed at the creation of a hybrid laser system which is composed of a gas lasers and a nonlinear crystal and appreciably broadens and enriches the radiation spectrum of these lasers. A highly efficient conversion (37%) is attained when generating the second harmonic in a ZnGeP₂ crystal owing to an increase in the peak power of CO laser radiation in the mode locking regime. The two-cascade conversion (generation of both sum and difference frequencies) of radiation of a broadband CO laser in the single sample of such nonlinear crystals as ZnGeP₂ and AgGaSe₂ is demonstrated. In this case, the radiation spectrum is broadened by nearly a factor of two, and the number of detected spectral lines grows by a factor of four. The use of a comparatively simple laser system of gas-discharge CO and CO₂ lasers to conversion in AgGaSe₂ results in laser radiation tunable over a set of narrow spectral lines within a range from 2.5 to 16.6 μm (more than two and a half octaves).     

Absorption by CS<Subscript>2</Subscript> molecules on “hot” band emission lines from a TEA CO<Subscript>2</Subscript> laser

We have measured absorption of emission from a TEA CO₂ laser, lasing on hot band lines, in pure CS₂ and a mixture of CS₂ with air, and we have determined the optimal lines for optical excitation. Numerical modeling has shown that as the peak intensity of the pump radiation is increased, we observe absorption saturation, the extent of which decreases as the pressure increases. The major factor responsible for absorption saturation is the “rotational bottleneck” effect. Depending on the peak intensity of the radiation, addition of a buffer gas can lead to an increase or decrease in the absorption. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 61–66, January–February, 2007.     

Helium-free operations in mini-TEA CO2 lasers

Summary Large helium-free emissions are obtained in two mini-TEA CO₂ lasers, by using always a corona preionization without additives and with a maximum energy density of 900J/l in the discharge. In general, helium-free emissions are more stable, but the best condition in efficiency, energy and peak power is observed always with a small He content added to the laser mixture.

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Riassunto L'uso di una piú efficiente preionizzazione a corona ha permesso l'operazione di un laser a CO₂ senza elio a pressione atmosferica con elevate densità di energia nella scarica (900 J/l) e grande efficienza di conversione dell'energia elettrica in radiazione laser.

     

10 kW cavity operation of a submillimetre CH3F laser

Operation of a CH₃F laser at 496μ has been obtained in a hemispherical optical cavity pumped by up to 42 J of 9.55μ CO₂ TEA laser radiation. Highly modulated 1μ pulses delivering 6 mJ at peak powers greater than 10 kW have been recorded.     

Application of a CW chemical laser for remote pollution monitoring and process control

The measurement of the concentration of gaseous hydrogen fluoride in the exhaust of an aluminum plant by resonance absorption of the radiation of a cw chemical HF laser is reported. The HF concentration has been evaluated taking into account the simultaneous absorption of water vapor and carbon dioxide at the HF laser frequencies. The absorption cross sections for H₂O and CO₂ at the HF laser lines have been determined in laboratory experiments.     

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 %.     

New far-infrared emissions and frequency measurements in hydrazine

By means of a new CO₂ laser we performed a new investigation of the far-infrared laser emission spectrum of hydrazine excited by the 10P(32) and 10R(8) CO₂ laser lines. We found seven new lines and measured the frequency of four of them; moreover we measured the frequencies of two more lines previously reported in the literature with only wavelength measurements. The frequencies of the far-infrared laser emissions have been measured by means of a frequency-synthesis chain based on new InP Schottky diodes. The detected signal was beat-note generated in a Schottky diode between the far-infrared radiation, the harmonics of a 72 GHz frequency reference and a rf signal. We also characterized all of the observed lines by their polarization relative to the pumping CO₂ laser, the optimum pressure and the offset relative to the CO₂ center frequency. PACS 42.55.Lt; 42.62.Fi