Ultrafast X-Ray Sources and Spectroscopy

The physics of ultrashort-pulse x-ray sources and their applications to ultrafast science are investigated.  

Laser-Produced X-Ray Sources

We have experimentally demonstrated a controllable ultrafast broadband radiation source in the extreme ultraviolet for time-resolved dynamical studies in ultrafast science. Ultrashort laser pulses are focused onto solid targets.
---This plot shows time-resolved spectra of laser-produced continuum XUV radiation (near 50 angstroms) emitted from a gold target for three different values of the laser intensity, ranging from 10^17 W/cm^2 (left), 10^16 W/cm^2 (middle), to 10^15 W/cm^2 (right), taken with a streak camera coupled to a grazing-incidence spectrometer. The emission at low intensity is less than 5 picoseconds in duration, which is the limit of the streak camera time-resolution. It can be seen that the x-ray pulsewidth can be arbitrarily adjusted by simply adjusting this single parameter (I), and thus the peak temperature of the plasma. A simple analytical model and a computer model of the laser-plasma interaction were both found to predict this same behavior.

Short pulse continuum x rays can also be used as a flashlamp for pumping transient recombination x-ray lasers.

Another short pulse (femtosecond) short-wavelength radiation source under investigation is an ultraviolet free-electron laser based on chirped-pulse amplification.

Ultrafast Applications

The above-mentioned source is now being used to study the transient behavior of atomic processes in plasmas. Time resolution is obtained with either a synchronized jitter-free streak camera or a pump-probe geometry.

This figure shows the pump-probe set-up. 

This figure shows the ionization dynamics on a picosecond time-scale of a laser-heated Aluminum sample, specifically, shifts in the L-edge in the absorption spectrum. 


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