D. J. Walker

Low-energy pumping of a 108.9-nm xenon Auger laser.

We report extensive measurements of gain in the Xe III system initially observed by Kapteyn et al. [Phys. Rev. Lett. 57, 2939 (1986)]. The dependence of this gain on pressure, pumping-pulse length, and pump energy is presented. By optimizing these parameters we have achieved a gain of exp(3.2) by using only 0.56 J of 1064-nm energy on target, representing an efficiency improvement of nearly 100. Total gains as high as exp(6.6) have been measured when using higher energies. Our data indicate that effective laser-produced plasmas can be created with applied power densities as low as 5 x 10(10) W cm(-2).

Quasi-metastable quartet levels in alkalilike atoms and ions.

We describe the properties of a subclass of quartet levels of alkalilike atoms and ions that often retain metastability against autoionization and may have large radiative yields. Gain cross sections for XUV lasers with wavelengths between 20 and 100 nm are given.

Observation of super Coster-Kronig-pumped gain in Zn III

We report the observation of laser gain in the vacuum ultraviolet pumped by super Coster-Kronig decay. Using a 5-J, 300-psec pump pulse of 1064-nm radiation, we have observed gain on transitions in Zn III at 127.0, 130.6, and 131.9 nm with total gains of exp(2.4), exp(5.1), and exp(3.2), respectively. The large branching ratios of the rapid super Coster-Kronig decay into a small number of final levels makes high-efficiency operation possible.

Proposal for an extreme-ultraviolet Auger laser at 63.8 nm in Cs iii

A system is proposed in which Cs atoms photoionized by soft x rays from a laser-produced plasma undergo selective Auger decay, causing inversion and lasing at 63.8 nm in Cs iii. Rate-equation calculations show that lasing should occur when a small (1-J) 532-nm pump laser is used. A similar system in Rb iii is briefly discussed.

Measurement of lithium and sodium metastable quartet atoms in a hollow-cathode discharge.

We report the measurement, in a pulsed hollow-cathode discharge, of metastable quartet atoms of Li and Na. By using a tunable probe laser, population densities of 3x10(10) atoms cm(-3) and 10(11) atoms cm(-3) were measured in the Li(1s2s2p)4P degrees and Na(2p(5)3s3p)(4)D(7/2) levels, respectively. These levels are candidates for energy storage for extreme-ultraviolet lasers.

Emission at 1091 A in neutral core-excited Cs

Certain quartet levels in alkali-like systems retain metastability against autoionization while acquiring large radiative yields. This quasi-metastability occurs through selective coupling to non-autoionizing doublet levels by the spin-orbit interaction. An example of such a level is the 5p/sup 5/5d6s /sup 4/P/sub 5/2/ level of neutral Cs, which has a calculated branching ratio for radiation at 1091 A of 43%. Experimentally, we find that this line has an emission intensity equal to 1/6 of that of the strongest ion line of Cs/sup +/, and is a promising candidate for an extreme ultraviolet laser.

Soft x‐ray pumping of inner‐shell excited levels for extreme ultraviolet lasers

We report the construction of a facility for investigating x‐ray pumping of extreme ultraviolet lasers. Measurements of large excited populations in Li+ and an investigation of a Li+ ‘‘shake‐up’’ laser are described.

Grotrian diagram of the quartet system of Na I

Laser enhanced fluorescence experiments have been used in conjunction with Hartree‐Fock calculations and emission studies to identify and locate Na I core‐excited quartet levels. Twenty‐eight Na emission lines are identified as transitions between these levels.