X-ray generation in a cavity heated by 1.3- or 0.44-μm laser light. I. Time-integrated measurements

The x-ray radiation generated in gold cavities (diameter 250–1000 μm) that were heated by 300-ps laser light pulses with a wavelength of 1.3 or 0.44 μm has been experimentally investigated. The absorbed laser intensity, averaged over the inner surface of the cavity, was varied in the range 2×${10}^{12}$–5×${10}^{13}$ W ${\mathrm{cm}}^{\mathrm{-}2}$. Laser light absorption was measured with an Ulbricht box. The cavity heating process was investigated by x-ray pinhole photography and time-resolved optical shadow- graphy. The radiant energy flux in the cavity and its spectral distribution were measured at three different locations in the cavity by spatially resolving transmission grating spectrometers. The experiments performed at the wavelength of 1.3 μm show low (∼30%) laser light absorption, delocalized heating due to refraction of laser light, and hard x-ray emission due to fast electron generation in the cavity. The 0.44-μm experiments show >80% absorption, localized heating at the laser-irradiated back wall of the cavity, and comparatively low hard x-ray emission. A maximum brightness temperature of 1.5×${10}^6$ K was measured in the smallest cavities.