Thomas F. Deutsch

MOLECULAR LASER ACTION IN HYDROGEN AND DEUTERIUM HALIDES

Laser action has been observed on vibrational‐rotational transitions between low lying vibrational levels of HX and DX (X = F, Cl, Br) formed by chemical reactions in an electrically pulsed discharge. HF wavelengths, lying between 2.7 and 3.3 μ, and DF wavelengths, lying between 3.6 and 4.2 μ, are listed and identified.

Laser window materials — An overview

The laser window problem is reviewed with emphasis on failure mechanisms, absorption processes, and material evaluation. Failure by thermal fracture and by optical distortion is discussed and the material parameters needed to calculate figures of merit for these failure modes are tabulated for a variety of materials. The exponential dependence of absorption coefficient on wavenumber for intrinsic multi-phonon processes is discussed and its use in discriminating extrinsic from intrinsic absorption emphasized. Laser calorimeter absorption measurements at 10. 6 Μm and 5. 25 Μm are described and the measured values tabulated. The use of internal reflection spectroscopy to examine the effect of various surface treatments on

cw OPERATION OF HIGH‐PRESSURE FLOWING CO2 LASERS

The performance of N2–CO2–He lasers operating at pressures in the 10–120‐Torr range and with nitrogen flow rates of 20–90 standard liters per minute is discussed. A 10‐cm‐long, 13.5‐mm‐i.d. discharge tube produced 140‐W output power. These lasers operate as in‐line mixing lasers, producing about one photon per excited nitrogen molecule. Cooling is provided by rapid removal of hot gas from the discharge region.

LASER EMISSION FROM HF ROTATIONAL TRANSITIONS

Laser action has been observed on pure rotational transitions of HF formed by a chemical reaction in an electrically pulsed discharge. The wavelengths, lying between 10.2 and 21.8 μ, are listed and identified.

Gain and fluorescence characteristics of flowing CO 2 laser systems

Single-pass gain has been measured for flowing CO 2 , CO 2 -N 2 , CO 2 -He, CO 2 -N 2 -He, and CO 2 -N 2 -H 2 mixes. The gain for CO 2 -N 2 mixes varies as d-0.9, where d is the tube diameter. The diameter dependence of the gain is less pronounced for CO 2 - N 2 -He mixes; a peak gain of 4.7 dB/m was obtained in a 1/2 in diam tube. Fluorescence data indicate that the upper laser level population is saturated at 100 mA in all cases. The addition of He, H 2 , or O 2 depopulates the lower laser level; helium further increases the population of the upper laser level. The addition of CO increases the population of the upper laser level, probably by resonant transfer from the excited vibrational states of CO.

BROAD‐BAND LIGHT AMPLIFICATION IN ORGANIC DYES

Two organic dyes previously used as liquid lasers, DTTC and cryptocyanine, have been used as broad‐band (>300 A) pulsed light amplifiers in the 7000–8500 A range. If the input frequency is close to the frequencies of the usual laser oscillations, the latter are quenched and the energy transferred to the frequency being amplified.

FREQUENCY‐ AND TIME‐DEPENDENT GAIN CHARACTERISTICS OF LASER‐ AND FLASHLAMP‐PUMPED DYE SOLUTION LASERS

Dye solution lasers are observed to lase at shorter wavelengths when laser pumped than when flashlamp excited. A comparison of the computed frequency‐ and time‐dependent gains for the two pumping methods explains this behavior and the observed Q dependence of the lasing frequency. This treatment also suggests a new technique for frequency tuning dye lasers.

Infrared third-harmonic generation in molecular gases

We report the first observation of third-harmonic generation (THG) in molecular gases. Using a CO 2 TEA laser and choosing molecules with vibrational transitions that contribute to a resonance enhancement of the third-order susceptibility tensor we have studied absolute conversion efficiencies, spectral response, and pressure dependences for THG in SF 6 , BCl 3 , and CO and compared the results to theoretical predictions.

4B2 - Pulsed and steady-state infrared emission studies of CO 2 laser systems

Transient and steady-state infrared emission at 2.5 to 15 μ from low-lying vibrational-rotational levels of CO 2 has been studied using a dc discharge. The time-dependent behaviors of several levels important for laser excitation and relaxation were examined following a pulsed discharge. The decays were, in general, different and were not simple exponentials. Relaxation of vibrational energy of CO 2 appears to occur by collisions involving vibration-vibration exchange between different vibrational modes and vibration-translation relaxation of the bending mode. The rate of transfer of vibrational excitation from N 2 to various vibrational modes of CO 2 was investigated as a function of CO 2 pressure. The addition of He reduced the emission from the lower laser levels with respect to that from the upper laser level and increased the nonradiative decay rate of the lower vibrational levels by CO 2 -He collisions. Under pulsed excitation, in addition to CO 2 laser action nearly coincident with the pulse, a weaker, delayed output was observed.

Effect of Hydrogen on CO2 TEA Lasers

The addition of several Torr hydrogen to a transversely excited pulsed high‐pressure CO2 laser using continuous shaped electrodes has been found to suppress the formation of bright arcs and lead to better pulse‐to‐pulse reproducibility. The hydrogen increases the threshold energy for arc formation and leads to as much as a factor of 2 increase in the power output of the laser. The gain of the laser is also increased by the addition of hydrogen.