The dual laser plasma photoabsorption technique has been used to measure the time-resolved vacuum-UV photoabsorption spectrum of a chromium plasma. Resonant photoabsorption cross sections, constructed with the aid of Hartree-Fock calculations, and weighted in accordance with the plasma temperature, have been used to produce the synthetic Cr2+ spectra. The relevant plasma temperature and ionization balance are obtained from simple analytical models for various times during the expansion phase of the plasma plume. The experimental spectra taken at delays of 32, 62 and 90 ns compare well with Cr2+ spectra computed for corresponding predicted temperatures. It is found that in order to produce synthetic spectra that match experiment well, it is necessary to take into account absorption from many states belonging to the Cr2+ ground state configuration 3p63d4, while states from the nearest metastable configuration 3p63p34s make a negligible contribution.

A finite element model including plasma simulation is used to calculate the amplitude of acoustic resonances in HID lamps in a 2D axisymmetric geometry. Simulation results are presented for different operation parameters and are compared with experimental data.

High intensity discharge lamps can experience flickering and even destruction when operated at high frequency alternating current. The cause of these problems has been identified as acoustic resonances inside the lamp's arc tube. Here, a finite element approach for the calculation of the acoustic response function is described. The developed model does not include the plasma dynamics.

We describe a recently designed and constructed system based on a 1 m normal incidence vacuum monochromator with corrected ͑toroidal͒ optics that produces a wavelength tuneable and collimated vacuum-ultraviolet ͑VUV͒ ͑ϭ30-100 nm͒ beam. The VUV continuum source is a laser-generated gold plasma. The primary function of the system is the measurement of time resolved ''images'' or spatial distributions of photoabsorption/photoionization in expanding laser plasma plumes. This is achieved by passing the beam through the sample of interest ͑in our case a second synchronised plasma͒ and recording the ''footprint'' of the attenuated beam on a charge coupled device. Using this VUV photoabsorption imaging or ''shadowgraphy'' technique we track and extract column density distributions in expanding plasma plumes. We can also measure the plume front velocity. We have characterized the system, particularly in relation to spectral and spatial resolution and the experimental results meet very well the expectations from ray tracing done at the design phase. We present first photoabsorption images and column density distributions of laser produced Ca plumes from the system.

We present results from a vacuum-ultraviolet ͑VUV͒ ''photoabsorption imaging'' technique based on the measurement of the time and space resolved absorption of a quasimonochromatic VUV beam from a laser plasma light source. The use of VUV radiation as a probe beam permits direct access to resonance lines of ͑singly and more highly charged͒ ions and also to the resonant and nonresonant continua of atoms and ions. In this experiment we have confined ourselves to measurements using the 3p -3d resonances of Ca, Ca ϩ , and Ca 2ϩ as markers of the temporal and spatial distribution of ground state atoms and ions in an expanding laser plasma plume. We show how time resolved column density maps may be extracted from such images. In addition we have extracted plasma plume velocities from the data, which compare well with an analytical laser ablation model.