Generation of copper Kα and Kβ pulses by the use of middle infrared laser system

A German and Austrian group has recently developed a table-top X-ray source based on ultra-short laser pulses. Generation of X-ray pulses by lasers may not be a big surprise for readers (See, for example, "Ultrafast X-ray Pulses from Laser-Produced Plasmas" by M. M. Murnane, Science, 251, 531 (1991), "Microfocus Cu Kα source for femtosecond x-ray science" by N. Zhavoronkov, Opt. Letter, 30, 1737 (2005)). However, so far, the X-ray intensity has not been sufficient for use in practical measurements such as pump-and-probe time resolved X-ray analysis. This time, scientists employed a mid infrared wavelength (3.9 micron) to accelerate electrons from the copper tape target to very high kinetic energy by making use of its comparably long optical period. The pulse width of the laser employed is 80 femto second. It was found that the system gives 10⁹ copper Kα photons per pulse generated with pulses of a peak intensity of 6×10¹⁶ W/cm². This is about 25 times higher than that generated by 800 nm wavelength laser pulses. For more information, see the paper, "High-brightness table-top hard X-ray source driven by sub-100-femtosecond mid-infrared pulses", J. Weisshaupt et al., Nature Photonics, 8, 927 (2014).