Search

Experiments were carried out to investigate the propagation of a cw CO2 laser beam through an absorbing slightly supersonic flow. A 500‐W CO2 beam was propagated through a small blow‐down wind tunnel operating with an air/SF6 mixture in order to simulate a high‐power beam propagating through the atmosphere. A collinear schlieren system was used to observe the density gradients caused by the absorbed power. Large density gradients were observed at a Mach number of 1.17; however, they were not shock initiated and their magnitude was not inconsistent with a heat‐balance analysis. Under the conditions of the experiment no shock waves were observed, even though their occurrence was predicted by a simple one‐dimensional analysis. From this study it is concluded that shock waves will not occur under most conditions encountered by high‐power cw CO2 laser radiation in the atmosphere. The presence of subshock density gradients and their effect on the propagating beam require further study.

Measurements of instability onset in a spatially uniform electron‐beam‐sustained KrF* laser discharge have shown that the time at which instability occurs decreases from about 1 to 0.1 μsec as E/n is increased in the range required for efficient laser operation. This finding is in good agreement with computed ionization instability onset times determined on the basis of a comprehensive model of the discharge.

The breakdown threshold with 10.6−μ wavelength CO2 laser radiation induced by particles is reported. Single solid particles of different materials and sizes were suspended electrodynamically at the focus of a pulsed TEA laser and the thresholds for vaporization and also for particle−induced breakdown were measured. Th threshold intensity for breakdown is of the order 108 W/cm2, independent of particle size and material and represents the limiting intensity that can be propagated through an aerosol−laden atmosphere.

Experiments have been carried out to study the nonlinear distortion of a laser beam due to absorption by aerosol particles in the air. A 15−W 10.6−μ beam was passed through a 1.5−m cell containing a carbon aerosol in air at STP, and various measurements of the distorted beam profile were made. The data show that aerosol absorption can lead to severe nonlinear distortion and that, for the regime in which the beam transit time is long compared to the interparticle thermal diffusion time, this distortion is qualitatively similar to that produced by molecular absorption, but has a magnitude somewhat below that predicted by conventional thermal blooming theory.

Experimental and theoretical studies of an optically pumped electric discharge laser in helium‐nitrogen mixtures are described. While the inherent efficiency of this system is rather low, these studies illustrate the basic parameters controlling the dynamics and efficiency of such a laser. In the experiments, intense diffuse discharges were obtained at pressures up to 12 atm and amplified spontaneous emission along the axis of the discharge was observed. The numerical modeling studies showed qualitative agreement with the experimental data and gave an optimized value of the kinetic coupling efficiency (absorbed 10.6‐μ power to uv laser power) of 1.6% and of the total efficiency (energy stored in the TEA laser supply to uv output energy) of 0.1–0.2%.

Results are reported of an investigation of fundamental kinetic processes influencing discharge and laser properties typical of the 502‐nm HgBr(B→X)/HgBr2 dissociation laser. Specific attention is focused on conditions representative of electron‐beam‐controlled discharges. Experimental results and corresponding analysis and interpretation are presented for several laser mixtures, focusing particularly on the factors affecting discharge characteristics and HgBr(B) formation. A set of phenomenological electron‐HgBr2 cross sections inferred on the basis of analysis of experimental observations is presented, along with a discussion of the effect of electron‐electron collisions on medium properties at the level of fractional ionization typical of the HgBr(B)/HgBr2 laser.

The connection between the virial theorem and the variational principle with respect to nonlinear parameters has been investigated for a system of n particles interacting through Coulomb forces. It is found that if the nonlinear parameters are chosen to be n scale parameters and considered as the components of a position vector in an n‐dimensional Euclidean space, the locus of points for which the virial theorem is satisfied is a path of steepest descent on the energy surface. It is thus possible to minimize the energy along a path of steepest descent without the necessity of calculating derivatives. As an example, variational wavefunctions and energies are obtained for the 31D and 33D states of the helium isoelectronic series through Z = 30, with the trial function a 39‐term configuration‐interaction expansion in members of a denumerably complete basis set. The calculated energies for He and Li+ agree with observed values to within 0.000007 a.u. The agreement with energies obtained from Hylleraas‐type ex...

The ground states of the first four members of the helium isoelectronic series and the 22S and 22P states of lithium are calculated using a configuration‐interaction expansion in a complete denumerable set of single‐particle functions, with one adjustable scale parameter. The best energies for the two‐electron systems, obtained with 120‐term expansions, are E(H−) = −0.52748, E(He) = −2.90335, E(Li+) = −7.27945, and E(Be+ +) = −13.65504, in units of e2/a0. The energies for all but He are lower than any heretofore obtained with a configuration‐interaction approach. The dependence of energy on scale factor is found to be very pronounced, in contrast to the corresponding behavior for wavefunctions which contain the interparticle coordinates explicitly. The best energies for the lithium states, obtained with 208‐term expansions, are E(22S) = −7.47369 and E(22P) = −7.40366. The 22S energy is not as good as has been obtained with either expansions in terms of interparticle coordinates or configuration interactio...

Techniques are described for prolonging the duration of stable e‐beam‐controlled excimer laser discharges, including: temporal tailoring of either the discharge voltage or the ionization source and kinetics modification by way of additives. Theoretical and experimental results are presented for KrF* laser discharges.

A new technique for pumping uv laser transitions is described. The technique consists of using an intense 10.6‐μ laser pulse to drive a diffuse discharge in a preionized uv laser medium. Because of its fast rise time, high electron density, and ability to operate at high pressure, this discharge is well suited to pumping uv laser transitions. Experimental results are shown for the application of this technique to the 3371‐A transition in nitrogen. A diffuse discharge at atmospheric pressure was obtained, and an intense pulse of 3371‐A radiation was observed.

XeCl(B) formation processes are examined for conditions typical of a discharge‐excited laser using HCl as the chlorine donor. It is shown that vibrational excitation of HCl followed by dissociative attachment is a primary step in the reaction sequence resulting in Cl− . XeCl(B) formation is the result of a three‐body Xe+ ‐CL− recombination reaction. Experimental results are presented which demonstrate efficient (∼2%) XeCl laser operation in an e‐beam assisted discharge in which over 75% of the energy was deposited by the discharge.

The atomic form factor for neutral carbon has been calculated with a Hartree–Fock wavefunction and with three configuration‐interaction wavefunctions of varying accuracy. Values obtained with the variational wavefunctions differ from Hartree–Slater values by several percent for all values of the momentum transfer. For all but quite small values of the momentum transfer the difference between variational and Hartree–Fock values lies between 0.10% and 0.15%.

Variational wavefunctions and energies have been obtained for the n1D, n3D, n1F, and n3F (through n = 8) levels of the helium isoelectronic sequence through Z = 16. The trial functions are configuration–interaction expansions in members of a denumerably complete basis set (Sturmian functions), with 39 terms used for the D states and 18 terms used for the F states. Differences between calculated and observed D state energies of He and Li+ range from 0.000001 to 0.00005 a.u.

Experiments have been carried out to study the ionization buildup and gas breakdown processes in the focal volume of an intense 10. 6‐μ laser pulse in atmospheric‐pressure helium preionized to various levels of electron density. With no preionization the laser flux required for breakdown was in agreement with results obtained by previous authors, and showed the same dependence on the focal volume size. However, with a high initial electron density, the threshold was much lower and showed no volume dependence. The results indicate that with preionization the breakdown threshold is controlled by cascade ionization processes, while with no preionization it is dominated by other effects such as small impurity particles in the gas, and that these other effects may be responsible for the diameter dependence of the breakdown threshold.

This letter reports the results of an investigation of HgBr(B2J+→X2J+) laser oscillation at 502 nm in Xe‐HgBr2 mixtures excited using an electron‐beam‐controlled discharge. Measured values of instantaneous electrical‐optical energy conversion efficiency were 2%, a level substantially higher than that typical of N2‐HgBr2 mixtures. Calculations show that efficiencies of 5–10% may be possible under optimized conditions.

He isoelectronic series ground state wave functions and energies, extending configuration interaction method through Z equals 10

Straightforward evaluation of electronic interaction integrals for many‐electron atoms using Laguerre polynomial radial wavefunctions leads to sums of differences of large numbers. An alternate formulation is presented which does not have this disadvantage.