In this paper we present the results of an experimental study of electronic energy transfer in xenon‐argon, krypton‐argon, and xenon‐krypton gaseous mixtures excited by a pulsed electric discharge. Spectroscopic evidence for electronic energy transfer is based on the decrease in the intensity of the vacuum ultraviolet emission of the excited diatomic homonuclear rare gas molecules in the presence of small amounts (10–1000 ppm) of a foreign rare gas atom, while the visible emission spectrum of the host gas is parctically unmodified under these conditions. The relative contributions of two energy transfer mechanisms involving atom‐atom and molecule‐atom energy transfer were established by a kinetic analysis of the dependence of the energy transfer efficiency on the host pressure. We have determined the cross sections for energy transfer from the lowest metastable Ar and Kr excited states, and from the lowest excited state of Ar2* and Kr2* to ground state Xe, and from metastable excited Ar and from Ar2* to ground state Kr. The molecule‐atom energy transfer process is characterized by large ∼ 10−14 cm2 cross sections. A simplified theoretical treatment of excited molecule‐ground state atom collisions provides a proper rationalization of these large cross sections in terms of long range dipole‐dipole coupling.

Electronic Energy Transfer Phenomena in Rare Gases

The cross sections are reported for the collisional excitation of the ground state of hydrogen, H2X1∑+g (v″=0), leading to vibrational excitation of all fourteen v″ levels. These cross sections pertain to energetic electron collisions populating the B1∑+u and C1∏±u electronic states which in turn radiate to the X1∑+g(v″) levels. The cross sections are in the range 10−18–10−17 cm2. An estimate is made of contributions from higher states.

Cross sections for the vibrational excitation of the H2(X1∑+g) state via electron collisional excitation of the higher singlet states

Broad‐band vacuum ultraviolet (VUV) fluorescence has been observed in Nd3+‐, Er3+‐, and Tm3+‐doped LaF3, YF3, LiYF4, and LuF3 by electron‐beam and VUV excitation. The VUV excitation spectra indicate a large Stokes shift (≳5000 cm−1) and a high fluorescence quantum yield of 0.8. The threshold power for laser action in these crystals by optical pumping has been estimated. Using a molecular H2 laser as a pumping source, a laser system which is tunable from 1650 to 2600 A could be constructed.

VUV fluorescence of Nd3+‐, Er3+, and Tm3+‐doped trifluorides and tunable coherent sources from 1650 to 2600 Å

A review of recent developments in high-pressure pulsed molecular lasers is presented. Included are some experimental results on TEA lasers, E-beam lasers, and lasers using Blumlein excitation. Discussions of the kinetic modeling, the parametric behavior, and the characteristics of uniform discharges in the high-pressure pulsed CO 2 laser are given. Recent results on pulse-initiated chemical lasers, extremely high-pressure lasers, and high-repetition-rate TEA lasers are also discussed. Efforts to control and use the output from these devices are described, and an extensive list of references is given.

High-pressure pulsed molecular lasers

A review of the status of research towards achieving lasing action in the vacuum ultraviolet and soft X-ray spectral regions is presented. An analysis of the general problems likely to be encountered is accompanied by numerical results for those approaches currently considered promising. Progress on each approach is detailed and various possible methods of verifying the presence of gain with their relative merits are discussed. Research areas requiring Application of short-wavelength lasers also are given.

Review of short wavelength laser research

Using a short‐risetime traveling‐wave discharge system, lasing has been produced in molecular hydrogen in the 1600‐A region and confirmed by direct observation of extensive amplification in the direction of travel. Pulsewidths and powers on the order of 1 nsec and hundreds of kilowatts, respectively, are observed. The ten H2 lines resolved extend from 1567 to 1613 A in the Lyman band. The laser lines originate from transitions between the vibrational levels of the state B(2pσ1Σu+) and the higher vibrational levels of the ground state X(1s1Σg+).

Vacuum ultraviolet laser emission from molecular hydrogen

A unique gas laser system suitable for achieving more than a 100-kW peak power in the vacuum ultraviolet spectral region near 1600 A is described. First, the theory of the molecular hydrogen laser is presented. The novel operation of the device to generate a fast-rising current pulse which travels down the discharge channel at the velocity of light is described. Finally, the experimental verification of lasing and further characteristics of the device are given.

A. W. Ali

Papers

Vacuum ultraviolet laser emission from molecular hydrogen

Laser emission in the vacuum ultraviolet from molecular hydrogen