R. M. Hill

Visible absorption by electron-beam pumped rare gases

The temporal and spectral behavior of absorption in the visible by e -beam excited argon, krypton, and xenon have been investigated with and without additives. The probe light used was from an argon-ion pumped, tunable dye laser, or from the visible lines of the argon-ion laser itself. Strong absorption was observed at all wavelengths investigated (450-620 nm). Structured absorptions out of atomic and molecular excited states have been identified by their temporal, spectral, and pressure behavior. The ubiquity of these absorptions, which is not fully understood, should have serious implications for the development of new visible lasers that operate during the electron-beam pumping pulse.

Optical emissions of triatomic rare gas halides

We report in this paper the observation of optical emissions from triatomic rare gas halide molecules formed in excited high density rare gas–halogen mixtures. The broad‐band continuum emissions are identified as transitions between ionically bonded excited states (Rg+2X−) and repulsive covalent lower states that dissociate to ground state atoms. These emissions become predominant at high rare gas densities.

A new blue‐green excimer laser in XeF

A new blue‐green excimer laser has been demonstrated on the C‐A transition in XeF, with an output energy of greater than 1 mJ. Xe*2 excimer fluorescence at 172 nm was used to photodissociate XeF2, producing XeF[B (1/2)] and XeF[C (3/2)]. The B (1/2) state was collisionally relaxed to the C (3/2) state with an Ar buffer. Lasing then occurs sequentially on the B (1/2) ‐X (1/2) and C (3/2) ‐A (3/2) transitions. Measurements of the C‐A laser spectrum showed a peak wavelength of 483 nm with a bandwidth of 12 nm. This new laser is potentially highly efficient and scalable and should be tunable over a bandwidth greater than 40 nm.

Quenching of Ne, F, and F2 in Ne/Xe/NF3 and Ne/Xe/F2 mixtures

As part of a kinetic study of XeF laser media, we have followed the time evolution of the Ne*, F*, and F*2 densities in e‐beam excited Ne/Xe/NF3(F2) mixtures. The Ne* and F* densities were monitored by laser absorption while the F2* was observed in emission at 158 nm. Rate coefficients for the quenching of these excited states by Ne, Xe, NF3, and F2 have been determined. The radiative lifetime of the F2* was measured to be 41±4×10−9 sec.

Energy ordering of the excited states of XeF

Ar/Xe/NF3 mixtures were excited by the focused beam from an ArF (193 nm) laser. Xe+ ions are produced by two‐photon ionization, the electrons attach to make F−, and the ions recombine to make XeF*. Radiation is observed in the XeF(B 1/2) →XeF(X 1/2) bands near 351 nm and in the broader XeF(C 3/2) →XeF(A 3/2) band near 460 nm. At low background gas pressure, mostly B‐X uv emission is observed. As the argon pressure is increased to 1000 Torr, the visible/uv band intensity ratio increases to about 3 to 1. We conclude from these results that the C (3/2) state lies 700±70 cm−1 below the B (1/2) state. This conclusion should have a significant impact on our understanding of the fluorescence yields and laser performance of e‐beam‐excited XeF.

The possibility of an efficient tunable molecular iodine laser near 340 nm

We have observed intense band emissions between 340 and 344 nm from electron‐beam‐excited mixtures of high‐pressure argon gas and iodine vapor. This emission appears to be from molecular iodine. Using the 357.6‐nm band from an Ar/N2 mixture as a calibration, we have measured the fluorescence yield in this wavelength region to be 70±24%. From this we computed an over‐all fluorescence energy efficiency of 13±4%. Based on these observations, we suggest the feasibility of an efficient high‐energy electron‐beam‐pumped argon‐iodine laser. The gain of such an argon‐iodine laser should be comparable to that of the Ar/N2 second positive laser.

Measurement of gain on the XeF (C‐A) blue‐green band

Transient gain has been observed on the C→A transition of XeF*. Measurements made at 488.0 and 475.9 nm showed a peak gain of 8% through a short cell filled with Ar/Xe/NF3 mixtures and excited by a short electron‐beam pulse. A stimulated emission cross section of 5×10−18 cm2 is derived, consistent with the measured linewidth and radiative lifetime of the C‐A transition. Weaker amplification was observed at 514.5 nm.

Measurements of negative gain for Hg2 continuum radiation

Gain measurements have been made at wavelength intervals over the continuum bands of high‐pressure mercury excited by a short high‐intensity electron beam pulse. These measurements, which utilized both continuum and laser light sources, showed net absorption at all wavelengths tested. This indicates that Hg2* has a larger cross section for absorption than for stimulated emission to the repulsive ground state, and virtually elminates the chances of laser action on these transitions.

Collisional quenching and radiative decay of the mercury excimer

Abstract We have measured the molecular continuum radiation from Hg2* in the 4000–5000 A range; the excitation was produced by a high energy, short pulse electron beam. When the excimer concentration is large, the dominant loss process is biexcimer collisional deactivation. At lower concentrations the decay becomes exponential and a radiative lifetime of the continuum radiation of 14 ± 3 μsec is measured.

Optical frequency conversion processes in atomic Rydberg states

We present an analysis of optically pumping Rydberg states in alkalis to generate coherent lasers in the infrared and far‐infrared spectral regions. Based on the previous accurate experimental and theoretical data on these states, our conclusion is that such laser systems can be operated either pulsed or cw and possess narrow linewidths, high gains, and considerable tunability. Wavelengths near 16, 12, 8.6, and 7.7 μm which are of interest for isotope separation are achievable with milliwatt power levels. Specific examples for Na vapor are given.