Temperature M easurements of Laser Heated Cavities

The heating of small cavities with pulsed laser or particle beams makes it possible to study phenomena of high-temperature radiation hydrodynamics and the state of matter at very high pressure, i.e. the physics of stars, for the first time in the laboratory [1], In this note we report preliminary results of temperature measurements made with gold cavities irradiated by 60-100 J/300 ps pulses from the iodine laser Asterix III at wavelengths of Ä =1.3(im (1 to) and X = 0.44 (im (3 co). Cavities with 250-300 |am diam. and 1000 nm diam. were used. A 280 (am diam. cavity (with entrance hole for the laser beam and two diagnostic holes) as well as the geometry of irradiation and observation are shown in the insets of Figure 1. The fraction of laser radiation rejected by the cavity target was monitored with an integrating box fitted into the experimental chamber. Absolute measure­ ments of the x-ray radiation emanating through the diagnostic holes were made with a transmission grating spectrometer (TGS) and with two x-ray sensitive photo­ diodes (XRD). The TGS employed a 1000 lines/mm free­ standing gold transmission grating [2] integrated into a 25 (im diam. pinhole, thus providing spectral and spatial resolution. The spectra were registered on Kodak 101-01 film, digitized on a 2 D densitometer and computer un­ folded using the film calibration data obtained recently in our laboratory [3]. The two XRDs (copper cathode, rise­ time ~ 340 ps) received either unfiltered (XRD 1, open) or filtered radiation (XRD 2, 2 |am Makrofol filter). A bright­ ness temperature was derived from both measurements. The radiation time was measured independently with an x-ray streak camera to be 550 ps. The measured tempera­ tures are shown in Fig. 1 versus the absorbed flux S L = £ absA4rL, i.e. the absorbed laser power Eahs/ z L averaged over the inner surface A of the cavity (rL the laser