Ultrafast X-ray measurements of inertial atomic-scale motion

Demonstration of the ultrafast nature of laser produced betatron radiation

“…The betatron source, combining ultrafast duration, collimation, and keV energies, becomes one of the very few short pulse x-ray sources emerging from both the accelerator and plasma communities. [8][9][10][11] The detailed theory of betatron radiation has been extensively described in several publications. The principle is as follows: an intense laser focused in a plasma of helium generates, by the way of its ponderomotive force, a relativistic plasma wave with a first period consisting in an ion cavity, the so-called bubble.…”

“…Indirectly, information can be inferred by measuring the duration of the electron bunch ͑electro-optic sampling, transition radiation͒ or by crosscorrelating the visible part of the synchrotron radiation together with a femtosecond laser pulse. 11,12 To directly probe the x-ray pulse, a cross correlation between the x-ray pulse and an ultrafast Bragg switch, triggered by a visible femtosecond pulse, can be used. 13 The Bragg switch being capable to absorb or diffract x rays, the information on the x-ray pulse duration is obtained by recording its intensity I͑⌬t͒ ͑after diffraction by the switch͒ as a function of its delay ⌬t with respect to the visible pulse that triggers the switch.…”

“…11,[14][15][16] It has been characterized in a number of time resolved x-ray diffraction experiments using the laser-plasma K␣ and the femtosecond synchrotron sources. The shortest transition observed, corresponding to the time for the disorder to appear and the reflectivity to fall, is ϳ200 fs ͑fall from 90% to 10% of the incident x-ray intensity͒.…”

“…The shortest transition observed, corresponding to the time for the disorder to appear and the reflectivity to fall, is ϳ200 fs ͑fall from 90% to 10% of the incident x-ray intensity͒. 11 This implies that this Bragg switch does not allow the exact determination of I X ͑t͒, but can nevertheless provide an upper limit of the pulse duration in the femtosecond time scale. Here we have chosen the solid-liquid phase transition in indium antimonide ͑InSb͒ to characterize the betatron pulse duration.…”

Clocking Femtosecond X Rays

“…In order to determine the magnitude of this additional jitter we compared timing information obtained using EOS with that from a laser-pump-x-ray-probe study of ultrafast nonthermal melting of an InSb crystal [17]. A strong subpicosecond reduction in Bragg diffraction following intense laser excitation allowed for single-shot measurement of the relative arrival time of the x-ray pulse and pump laser pulse [18,19]. This independent and direct measurement of the relative x-ray timing was made in the x-ray experiment hutch and could be determined to within 50 fs.…”