David G. Sutton

Infrared Double Resonance in Sulfur Hexafluoride

The relaxation of sulfur hexafluoride has been monitored by observation of infrared absorption intensities following passage of an infrared laser pulse through the gas. The laser pulse saturates a small number of rotational lines in the ν3 ← 0 transition of SF6 at 944 cm−1, producing a transient “hole” in the absorption spectrum at that frequency. This hole is filled in very rapidly by rotational relaxation processes. The specific vibrational excitation is, at essentially the same time, transformed into a vibrational temperature in excess of the gass translational temperature, by means of very efficient vibration ↔ vibration energy transfer collisions. The energy released in this step also heats the gas translationally by the order of 25°K. The vibrational temperature then relaxes to the translational temperature by a binary collision process, with pτ = (122 ± 8) μsec·torr in pure SF6. The rate‐controlling step is concluded to be the vibration→translation relaxation of the ν6 level at 363 cm−1. The mean ...

Infrared saturation in sulfur hexafluoride

The saturation of absorption of a CW infrared laser beam by SF6 has been measured as a function of pressure of SF6 and added buffer gases (He, Kr, and C2H6). The results are interpreted by means of a four-state linear kinetic model for saturation of vibrational energy levels by intense infrared radiation, which predicts equalization of upper and lower level populations at power densities of approximately 10 W/cm2. Vibrational and rotational deactivation cross sections are derived from these data with the aid of this model, which suggests that previously observed pulse transparency effects may be interpreted in terms of this same model.

The UV‐visible spectroscopy of laser‐produced aluminum plasmas

The optical emission spectra (180–760 nm) of plasmas produced by a flashlamp‐pumped dye laser focused on an aluminum target have been recorded and analyzed. In the incident intensity range from near plasma threshold to 5×107 W/cm2 the electron temperature was calculated from the relative emission intensity of Al(II) states (Te=8.0×103 K). The electron density was determined from Stark broadened linewidths of four Al(II) lines. Both the spatial and temporal dependence of the emission spectra were obtained providing a map of the electron density and temperature.

Mechanism of passive Q switching in CO 2 lasers

Passive Q switching of a CO 2 laser by saturable absorbers is analyzed in terms of a four-state kinetic model previously used to interpret infrared saturations double resonance, and pulse transmission. Good agreement is found between the predictions of this model and the experimental dependence of such variables as pulsewidth, repetition frequency, and peak power on the presence of buffer gases mixed in with the absorber.

Observation of Laser‐Induced Acoustic Waves in SF6

The acoustic waves reported by Bates et al. are directly observed by means of a solid‐dielectric capacitance microphone. The initial time development of the pressure wave indicates that the vibration–vibration energy transfer rate in SF6 is not less than 2 × 106 sec−1·Torr−1.

Infrared pulse transmission in SF 6 -He mixtures

The transmission of Q -switched CO 2 laser pulses through SF 6 -He mixtures is studied experimentally and compared with predictions generated by computer calculations based on a four-state model for SF 6 . The results show that for saturating fields the factor determining the rate of absorption is the rotational energy transfer process that feeds the levels interacting with the laser. This conclusion has implications for models of passive Q switching in molecular lasers and infrared-infrared double resonance.

Behavior of a Pulsed‐Discharge Laser with an Intracavity Absorber

The asymmetrical pulse usually obtained from a transversely discharged medium‐pressure laser may be transformed into a narrower pulse with a higher peak by the incorporation of an absorber into the laser cavity. The experimental results are well predicted by a previously described model for passive Q switching.

Laser actinometry of flash-photolyzed H 2 /F 2 /He mixtures

Actinometric and time-to-threshold experiments with flash-initiated H 2 /F 2 /He mixtures have been modeled with the RESALE chemical laser code. Comparison of the salient features of both experiments with those predicted by the code determines the efficiency of our xenon flashlamp in dissociating F 2 . The results indicate that our 1000-J 20-μs full width at half maximum (FWHM) lamp is capable of dissociating 1.2 percent of the F 2 initially present in dilute F 2 /He mixtures.