Soft X-ray emissions from ultra-thin foiled targets irradiated with an intense pulsed laser

Kado, Masataka; Ishino, Masahiko; Kishimoto, Maki; Tamotsu, Satoshi*; Yasuda, Keiko*; Shinohara, Kunio*

Intense soft X-ray emissions are very useful for X-ray microscopy to observe living biological specimens. Increasing the photon flux in the range of wavelength 2.3 nm to 4.4 nm, so-called "water window", is a key issue for the soft X-ray microscopy. We have proposed to use ultra-thin foiled targets to limit the target mass to be heated by an intense pulsed laser. Thin foiled gold targets with various thicknesses from 10 nm to 50 m were irradiated with an intense laser pulse at the wavelength of 1.053 m generated from a Nd:glass laser system with 20 J output energy in 600 ps pulse duration. The soft X-ray emissions from the laser-produced plasmas were measured with a soft X-ray spectrometer and a soft X-ray plasma camera. The X-ray flux increased as the target thickness decreased and reached the maximum at the target thickness of 20 nm. We have observed living biological cells with the soft X-ray emissions generated from the thin-foiled gold targets.