A Kerr cell was utilized as an optical shutter to generate a shortened pulse and as an isolator between amplifiers in an iodine laser system. By rotating the polarization of incident laser pulse only during the timing window of high voltage applied to the Kerr cell, shortened pulses of 5 ns and 1 ns, corresponding to the difference in propagation time of two coaxial cables, were obtained. It was also noticed that more than one timing window of Kerr cell was produced with a long incident laser pulse from the oscillator. The measured transmittance of Kerr cell with respect to applied voltage was compared with the theoretical estimation using the electro-optic Kerr effect theory. Through the amplification of the shortened pulse in iodine amplifiers, a pulse of 0.5 GW(2 J in 4 ns) was obtained.
This amplified pulse was focused into a cylindrical carbon target through the lens of f = 30 cm to generate laserproduced plasma from which soft X-rays are emitted. A flat-field XUV spectrograph placed at 45˚ from the incident laser beam gave spectrally-resolved and time-integrated spectra recording the wavelength region of 30Å - 300 Å.
In a short pulse of 4 ns, the target was irradiated with the intensity of $I\approx1-6\times10^{12}W/cm^2$. And in a long pulse of about 70 ns, it was irradiated with the intensity of $2\times10^{11}W/cm^2$.
In the former case, when a prepulse was incident on the target ahead of the main driving pulse(4 ns) by 68 ns, the intensity of $L_\alpha$ has the superposed facet from the laserproduced plasmas of each pulse. From this result, it was found that the laser-produced plasma from the prepulse did not interact with the main pulse. In the latter case only the spectra of the ionization state of C Ⅳ and C Ⅲ were shown. It was revealed that the line spectra were dominant in the emission from He- (C V) and H-like(C VI) resonance line. And He- and Li-like satellite lines due to dielectric recombination were also recorded. From this intensity ratio of He-like to Li-like satellite line, the electron temperature was approximately 60 eV. When the intensity of the incident pulse was high enough, $L_\beta$ and $L_\gamma$ spectra were observed specially from the second order of these spectra which are more sensitive spectral region of grating and continuum X-ray radiations were also increased.
