ABSTRACT
A pre-plasma was formed by irradiating the target at normal incidence with the long pre-pulse focused into a line of 30 |um FWHM width and 4.1-5 mm in length using the combination of a f = 67.5 cm focal length spherical lens and a f = 200 cm focal length cylindrical lens. The pre-plasma was rapidly heated with the short pulse impinging at a grazing incidence angle of 14 degrees to generate a transient population inversion. The short pulse was focused into a line of 30 |im FWHM width using a f = 76.2 cm focal length multilayer-coated parabolic mirror placed at 7 degrees from normal incidence (Fig. 4). The off-axis placement of the paraboloid forms an astigmatic focus that results in a line that is further elongated when intercepted at grazing incidence by the target to form a 4.1 mm FWHM line focus. Initial successful experiments were conducted using a f = 2 m spherical mirror to focus the short pulse beam. However, all the results discussed herein were obtained using the parabolic mirror. The overlap of the two line focus on target was monitored and adjusted by imaging the target onto a CCD utilizing digital zoom. The plasma emission was monitored using a flat field spectrograph composed of a 1200 lines per millimeter gold-coated variably space spherical grating placed at 87 degrees grazing incidence and a back-illuminated CCD detector array of placed 48 cm from the target. Taking advantage of the small dimension of the plasma no slit was used. Al filters of 0.3 um and 0.5 um thickness or their combination with a 0.14 |nm thick Zr filter were used. In some of the measurements the beam was further attenuated placing meshes of known transmissivity in front of the diffraction grating.
