K. Hohla

Diatomic interhalogen laser molecules: Fluorescence spectroscopy and reaction kinetics

Mixtures of halogen‐containing molecules and rare gases have been excited by a short pulse of high energy electrons. The D′→A′ transitions occurring between an ionically bound upper level and a weakly bound covalent lower level in the diatomic halogens F2, Cl2, and interhalogen compounds ClF, ICl, IF, IBr, BrCl, and BrF formed under these conditions have been studied systematically. Emission wavelengths calculated from a simple model are in good agreement with the experimental data. The processes responsible for the population of the upper level have also been studied. The exchange reaction of an electronically excited atom with a halogen donor molecule appears to be the key step in the kinetic excitation sequence. A rate equation model satisfactorily describes the time development of the observed halogen fluorescence. Based on these results, successful laser experiments have been conducted on several of the interhalogen systems.

UV laser induced molecular multiphoton ionization and fragmentation

Abstract It has been demonstrated that the output from a discharge pumped KrF laser (249 nm) is capable of ionizing a variety of molecules. The nature and yield of ions generated in this process, which have been identified by time of flight mass spectrometry, exhibit a striking intensity dependence.

Discharge Pumped F_sub.2 Laser at 1580 Alpha

Abstract By pumping mixtures of F 2 and He in a fast UV-preionized discharge we have obtained laser emission at 1578 A, probably stemming from the 3 Π 2g → 3 Π 2u transition in molecular fluorine. Observed energy is 8.5 mJ in pulses of 15 ns half-width. First experimental results on laser performance and scalability are given.

Gigawatt photochemical iodine laser

An oscillator‐amplifier iodine laser system has been set up to demonstrate the feasibility of high‐power operation of this laser. Pulse powers of 1.2 GW have been obtained with two amplifier stages. Technical details and relevant laser parameters are discussed.

Formation of Xe∗2 by collision pair absorption at 158 nm

Abstract Pair absorption from colliding Xe atoms of the molecular fluorine laser radiation is reported. The absorption coefficient for this process at 300 K was found to be α = (4.32 ± 0.1) × 10 -9 Torr -2 cm -1 . Fluorescence at 172 nm originating predominantly from the 1 Σ + u state of Xe ∗ 2 indicates that by this mechanism the Xe dimer laser can be pumped optically.

Interhalogen UV Laser on the 285 mm Band of CIF

Abstract A new UV-laser operating on the 285 nm band of ClF is reported. Fluorescence and laser oscillation on numerous vibrational and rotational lines has been observed following e-beam excitation of a Ne/F 2 /Cl 2 mixture. The upper laser level is probably formed in an ion recombination reaction of fluorine and chlorine ions.

Time‐resolved spectroscopy of the Ar* 2‐excimer emission

High‐pressure argon was excited by a 2‐ns 600‐keV e‐beam pulse, and time integrated as well as time resolved fluorescence spectra were measured. No significant dependence of line center (126.2±0.1 nm) or spectral width (80±10 nm) of the Ar2 continuum on gas pressure was found in the range 0.5–20 bar. From the buildup time constant of fluorescence we calculated the three‐body rate constant for Ar2 formation to be 5×10−33 cm6/sec. The fluorescence decay was found to consist of two exponentials with time constants 8.6 and 39.2 ns at 20 bar and 12.6 and 73.9 ns at 10 bar, respectively. We attribute this behavior to the fluorescence originating from the singlet and triplet upper state. From the spectral shift between the two components we determined the singlet‐triplet splitting in the excited Ar2 molecule to be 12 A corresponding to 760 cm−1.

100‐ps pulse generation and amplification in the iodine laser

We have generated 100–200‐ps iodine 1.315‐μ laser pulses by means of the free induction decay (FID) technique. A 2.5‐ns switched‐out pulse from a mode‐locked oscillator is truncated by generating its own gas breakdown in the focal spot between two lenses and then passed through a hot I2 absorber operated in the small‐signal regime to generate a short FID pulse. Streak camera studies of such pulses showed that the breakdown time was about 40 ps and the FID pulses had a full width at half‐maximum of about 100–200 ps. Subsequent amplification of a pulse showed that the 4‐GHz bandwidth of the atmospheric pressure iodine amplifier was insufficient to cover the pulse spectrum. A calculation of the pulse width based on the reduction of the small‐signal gain due to such spectral considerations also gave pulse widths in the 100–200‐ps range.

Terawatt Iodine Laser

In this paper the high power iodine laser ASTERIX III is described. It is a single beam system designed to yield an output power in the 1 Terawatt range (energy about 1 kJ, pulse duration about or less than 1 ns). It will be used for plasma production with power densities on the target surface expected in the range between 1017 to 1018 W/cm2.

New results with the 1 TW iodine high power laser Asterix III

The on-axis portion of the pulse was recorded both before and after the grating pair by a 5 psec resolution streak camera. Densitometer traces of a typical shot are shown in Fig. 1. The incident pulse [Fig. 1 (a)] has essentially the same shape and width as it had before the Cs cell ; however, at the output of the gratings [Fig. I (b)] it has broadened to approximately 45 psec, with a noticeable flattening around the top. No attempt was made to optimize the squaring effect in this experiment. Comparison of the densitometer trace with calculated output shapes suggests that the peak nonlinear phase shift B in the incident pulse was approximately 1.1 n, a value consistent with those measured in a related e~pe r imen t .~ For the dispersion and incident pulsewidth available here, the optimum squaring would occur for B Y 1.9 x , giving the result shown in Fig. 2 (a). The squaring effect of the gratings can be further enhanced by the use of a fast saturable absorber after the gratings, as indicated in Fig. 2 (b).