Molecular beam diagnostics by means of fast superconducting bolometer and pulsed infrared laser

The laser-bolometric infrared spectroscopy is an efficient method for measuring the internal energy distributions of molecular beams. Additional informations about the kinetic energy distribution of molecules in a selected internal state can be obtained from time resolved experiments. A fast superconducting bolometer and a pulsed infrared CO₂ laser have been used for testing the use of this technique as a universal tool for molecular beam diagnostics. Experimental results are presented and analyzed for pure SF₆ and helium seeded with 5% SF₆ beams. The efficiency of fast superconducting bolometers, used for molecular beam time-of-flight measurements, is discussed. A comparison is made between time resolved laser-bolometric technique and alternative molecular beam diagnostic methods.     

Intramode and Fermi relaxation in CO2, their influence on multiple-pass,short-pulse energy extraction

Analytical, experimental and numerical results concerning the influence of intramode and Fermi relaxation on multiple-pass, nanosecond-pulse energy extraction are presented. Multiple-pass energy extraction experiments show satisfactory agreement with the analytical and numerical calculations which predict a significant increase in extracted energy. In three passes, an amount of 9.7 J/l was extracted at an efficiency of 4.3%, These values are taken with respect to the volume of the beam inside the amplifier. In a single pass only 3.5 J/l was extracted.     

Dynamics of the CO2 lower laser levels as measured with a tunable diode laser

A tunable diode laser operating in the 4.3 m region is used to probe a conventional cw CO₂ laser discharge. Vibrational populations in the 10⁰0, 02⁰0, 02²0, and 01¹0 levels of CO₂ are measured under lasing conditions, i.e., in the presence of intense 10.4 and 9.4 m fields. The tunable diode laser is also used to monitor the energy transfer processes between the four levels after the passage of an intense 10.4 m pulse. The detailed information provided by the tunable probe laser enables us to determineseparately all the vibration-vibration (V-V) and vibration-translation (V-T) rate constants of importance in the relaxation of the lower laser levels in CO₂. The V-V rate constants are found to vary from a low value of 4.5×10⁴ s^–1 Torr^–1 for the coupling of 01¹0 to 10⁰0 to a high value of 8.0×10⁵ s^–1 Torr^–1 for the coupling of 01¹0 to 02²0.This work was supported by the National Science and Engineering Research Council of Canada and the Provincial Government of Ontario     

High-efficiency,high-energy performance of a pulsed HF laser pumped by phototriggered discharge

A comparison of the performance of pulsed infrared HF lasers pumped by phototriggered discharges using either Ne/SF₆/H₂ or Ne/SF₆/C₂H₆ mixtures are presented. For an active volume of 50 cm³, a specific output energy as high as 11 J/ has been achieved with an efficiency higher than 3% when C₂H₆ is used as H atom fuel. The replacement of ethane by molecular hydrogen reduces the laser performance by 40%. The investigation of the temporal evolution of the laser intensity shows that this dramatic decrease results from a shortening of the laser pulse duration rather than from a decrease of the peak power. Indications are given that this behavior is correlated to a very different temporal evolution of the discharge parameters, especially at low reduced electric field E/N.     

Investigation of the population inversion in a He-Ne laser discharge by heterodyne holographic interferometry

Heterodyne holographic interferometry was used for end-on investigation of a He-Ne laser discharge. By tuning an actively stabilized dye laser over the 633 nm neon atomic line the phaseshift was obtained as function of frequency, thus enabling the determination of spatially resolved population inversion.     

Confirmation of far infrared laser assignments from CH3-deformation and CH3-rocking states of optically pumped methanol

High-resolution Fourier transform spectroscopy has been applied to confirm previously proposed assignments for nine far infrared (FIR) laser lines from the CH₃-deformation state of CH₃OH and one line from the CH₃-rocking state. Accurate frequencies are deduced for the observed and other predicted FIR laser transitions. FIR torsional branch frequencies in the ground state which were used in the confirmation are presented. Comments are also made on the OH-bending mode of CH₃OH.     

An explanation of the direction of the relaxation in the HCN gas microwave laser,and a new assignment of further laser lines along the path of internal vibrational energy redistribution

We assume a direct connection between the shape of the anharmonic potential energy surface of a molecule and its internal vibrational energy redistribution. In the case of HCN there is a transition from convex to concave behaviour of the equipotential lines in the fundamental range. This explains the existence of the known laser transitions in the line systems of 11¹0–04⁰0 and 12⁰0, 12²0–05¹0, and leads to the assignment of further lines at 35.211, 18.335, and 14.792 cm^–1 to 10⁰0–03¹0, 03³0 and the line at 12.928 cm^–1 to 20⁰0–06⁰0. For the pure IVR transition we assume symmetry selection ±± without a Coriolis resonance.Presented in part at the 2nd International Symposium on Elementary Processes and Chemical Reactivity, Liblice, September 7–11, 1987     

IR and FIR spectroscopy of 13CD3OH around the 10P(22) and 10P(24) CO2 laser lines: New FIR laser emissions,frequency measurements and assignments

By using high resolution infrared Fourier transform data on ¹³CD₃OH and the 10P(22) and 10P(24) lines of a waveguide CO₂ laser to optically pump this methanol isotope, eight new FIR laser lines were observed. The frequencies of five laser lines were directly measured by heterodyne detection with already known laser lines. Particularly interesting are the lines pumped by the 10P(24) line, since a triade of emissions could be completely assigned.     

Self-focusing and defocusing of TEA CO2 laser radiation in NH3

We report on the observation of self-focusing and defocusing of TEA CO₂-laser pulses in NH₃. Self-focusing of the 9R(30) CO₂ laser line resulted in a significant spatial narrowing of the laser beam after propagating through a 100 cm long cell containing NH₃ at a relatively low pressure of 1 Torr. Spatial broadening, characteristics of self-defocusing, has been observed for the 9R(16) CO₂-laser line.     

Gain and saturation measurements in a discharge excited F2 laser using an oscillator amplifier configuration

The small-signal gain coefficient and the saturation intensity of a F₂ pulsed discharge molecular laser at 157 nm have been measured using two discharge devices in an oscillator-amplifier configuration. The small signal gain coefficient was measured to be 5.2±0.4% cm^–1 at 3 atm total pressure and 1.5 cm electrode spacing and 4.1±0.4% cm^–1 at 2 atm total pressure and 2 cm electrode spacing while the values of the saturation intensity were 5 MW/cm² and 4.6 MW/cm², respectively.     

Observation of new laser transitions and saturation effects in optically pumped NO

We report investigations of an NO laser employing specially profiled magnetic fields of up to 3.4T, and F₂ pump laser intensities as great as 20 MW cm^–2. We have observed laser oscillation at 226 nm on a rotational branch of the B'-X/it(3–11) band of NO for the first time, in addition to the previously reported oscillation at 218 nm on the B'-X/it(3–10) band. We have also observed visible laser emission on a rotational branch of the B ²-B ² II(3–1) band of NO. Saturation of the NO laser pulse energy with pump intensity has been observed, the total NO laser pulse energy having been increased to 490 J. The possibility of increasing the NO laser pulse energy towards 1 mJ per transition is discussed.     

An experimental study of self-focusing and self-defocusing of a TEA CO2 laser pulse in CDF3

We observed self-focusing and self-defocusing of a TEA CO₂ laser pulse in CDF₃ vapor under different conditions. The experimental parameters we varied are the pressure inside the interaction cell, the frequency of the laser, the energy and the temporal length of the pulse. We have shown that it is possible to pass from self-focusing to self-defocusing by only increasing the intensity of the laser pulse. We propose a physical model that can explain these experimental results. This model is different from that used to explain the selffocusing of a CO₂ laser in SF₆.     

Measurement and assignment of new FIR laser lines in12CH3OH and13CH3OH

We have found twelve new FIR laser lines in¹²CH₃OH and thirty three in¹³CH₃OH. Both molecules were pumped by a regular cw CO₂ laser. We have also assigned 20¹³CH₃OH laser lines to specific rotational energy levels in the excited C-O stretchhindered rotation combined states     

Numerical analysis of the electrical and optical behaviour of a pulsed nitrogen laser through time-dependent resistances and inductances

Received: 28 September 1996     

Output and picosecond amplification characteristics of an efficient and high-power discharge excimer laser

Improvements in output pulse energy and efficiency of a conventional capacitor-transfer-type discharge excimer laser with automatic preionization have been achieved by extending the discharge volume and resulting moderate pumping of the active medium. The discharge laser produces a pulse energy of more than 1 J for XeCl, KrF, and ArF lasers in square beams of about 2×2 cm², and the maximum overall efficiency observed is 2.9% for XeCl, 3.2% for KrF and 1.8% for ArF. The laser device has been involved in a picosecond ( 32 ps) XeCl laser amplification system, and was operated as an amplifier at a repetitive frequency of 10 Hz. Saturation fluence for XeCl laser was measured to be 1.4 mJ/cm², and the picosecond pulse energy of 40 mJ was extracted from the amplifier.On leave from Ebara Corp., 6-6-7, Ginza, Chuo-ku, Tokyo 104, JapanOn leave from Mitsubishi Heavy Industries, LTD., 4-6-22, Kan-on shinmachi, Nishi-ku, Hiroshima 733, Japan     

CW and pulsed FIR-CO2 hybrid laser with improved efficiency and amplitude stability at short FIR wavelengths

For the first time stable cw output of a FIR-CO₂ hybrid laser has been achieved at wavelengths shorter than 300 m. Due to the saturable absorber characteristic of the FIR laser gas, cw or pulsed emission is observed on both, the CO₂ and the FIR laser output, depending on the operating conditions. Results are reported on different resonant lines in CH₃OH and the 67 m Raman line in NH₃. The good efficiency of this laser is also demonstrated by the excitation of two new emission lines in CH₃OH, namely 49 and 56 m, pumped by 9R(22) and 9R(24), respectively.On leave from the Institute of Physics, University of Beograd YU-11000, Beograd, Yugoslavia     

The influence of superradiant relaxation on associative ionisation yield of laser excited potassium atoms

The influence of superradiant relaxation of excited 7P _1/2 potassium atoms on their associative ionisation yield has been investigated. The excitation was carried out by a laser pulse in a tube containing potassium vapour with concentration 10¹⁴ cm^–3. A seven-fold drop of ionisation yield was found and spontaneous luminescence pulse distortions by superradiance (SR) were measured in the wide interval of excited atoms densities N _e ⁰ 10⁸–10¹³ cm^–3. The values of associative ionisation rate constant and SR threshold atomic densities are obtained, and the shapes and quantum yields of SR pulses are evaluated from the experimental results.     

Performance of a ten-liter electron avalanche-discharge XeCl laser device

This paper describes the laser performance of an X-ray preionized ten-liter volume, electron-avalanche discharge XeCl system, operated at dc charging voltages of up to 70 kV both with and without X-ray preionization. An output energy of more than 11J uniformly distributed over a (7×10) cm² spot size was achieved using a multichannel spark-gap as the main discharge switch. The discharge was also successfully operated in the switchless mode, yielding a 4.8 J output energy and a 0.9% efficiency. The time-resolved gain measurements provided information on the laser discharge evolution.ENEA GuestENEA Guest on leave from the Shanghai Institute of Optics and Fine Mechanics, the Chinese Academy of Sciences, Shanghai, China     

High-pressure behaviour of an X-ray preionized discharge pumped XeCl laser

The output characteristics are described of an X-ray preionized discharge pumped XeCl laser, fed by a low-impedance pulse forming line (PFL), at pressures up to 12 bar. The influence of a multichannel rail gap placed between the PFL and the laser head on the output energy was studied. We found an increase of output energy with increasing pressure up to 8 bar. At higher pressures a saturation behaviour was found. The maximum output energy per unit volume was 6.5 J/l.