X-ray backlight streak method for laser fusion experiments

Observation of target implosion by time-resolved imaging of self-emitted x rays is not useful for the cannonball, since the temperature of the inner shell is similar to the brightness temperature of the drive x rays (typically 80-120 eV). Hence the authors developed an x-ray backlight streak (XBLS) method and have succeeded in making clear shadow images of the cannonball target implosion, they believe, for the first time. The laser used for this experiment was the frequency-doubled (0.53 μm in wavelength) Gekko XII glass laser. Square pulses of 1.3- and/or 2-ns duration were generated by a stabilized pulse-stacking technique. Two to four beams with a certain time delay were used to produce the x-ray backlight source, and the residual beams were injected into the cavity. Typical energy was 600-800 J/beam. The cavity radiation spectrum and its time history were measured using a transmission grating spectrometer coupled to x-ray film and an absolutely calibrated soft x-ray streak camera. To simplify the process, they used the cavity without an inner shell for this observation. To examine the uniformity of cavity radiation they compared the x-ray spectra from the two different cavity portions, one of which was directly heated with a laser (laser on), the other of which was heated with the cavity x rays (laser off)