Near-field measurements of subnanosecond-created laser plasmas

Publisher Website
Google Scholar
Abstract
The near field of expansion for plasmas created by a 40‐psec 1.0–1.5‐J laser has been probed to measure the electron density and local electric and magnetic fields. Holographic interferometry was used to measure the electron density in the range 1017 to 6×1018 cm−3 at delays of 2.5–22 nsec. Space‐charge electric fields of up to 1900 V/cm were detected by deflection of a fast He+ ion beam probe as late as 26 nsec after irradiation. Spontaneous magnetic fields of up to 50 G, rising in 10 nsec, were seen 4 mm from the target, decaying rapidly and often reversing at 8 mm. The temperature in the blowoff estimated from the combination of local electric field and electron‐density scale length is high compared to predictions based on a peak Te=160 eV inferred from a multichannel soft x‐ray spectral analysis. An anisotropic fast ion group appears in the interferometric density profiles and ejection of ∼109 fast electrons is observed in the electric field measurements. These effects are compared to the early time ion collector signal and nonthermal x‐ray spectrum, respectively.