Characterization of High-Harmonic Extreme Ultraviolet Radiation Generated by Two-Color Laser Field for Warm Dense Matter Research

Abstract

Extreme ultraviolet (EUV) light is suitable for studying the electron dynamics of warm dense aluminum. High-order harmonic generation (HHG) produces a coherent EUV, which is used as a probing light. HHG using the femtosecond Ti:Sapphire laser at a 800-nm wavelength generates only odd harmonics for 1.55 eV and cannot probe just below the aluminum L-edge. The absorption spectrum near the aluminum L-edge can be observed when the two-color laser field HHG increases probing points to narrow the spectral interval. A beta barium borate crystal can produce a second harmonic laser field (400 nm wavelength) and a 90° polarization for the fundamental laser field before the interaction between the laser and gas target. A two-color laser field comprising 800 and 400 nm passes through the HHG system to generate all integer order harmonics for 1.55 eV. The EUV signal by the two-color field exhibited a higher intensity than by the single-color field and was adopted to obtain the cold aluminum absorption spectrum. The absorption spectrum was compared with the CXRO data and is suitable for use as a probe beam in subsequent pump-probe experiments.