The temporal output of a Ti:Sapphire laser system has been optimized using an acousto-optic programmable dispersive filter and a genetic algorithm. In-situ recording the evolution of spectral phase, amplitude and temporal pulse profile for each iteration of the algorithm using SPIDER shows that we are able to lock the spectral phase of the laser pulse within a narrow margin. By using the second harmonic of the CPA laser as feedback for the genetic algorithm, it has been demonstrated that severe mismatch between the compressor and stretcher can be compensated for in a short period of time.
A terawatt tabletop laser wakefield acceleration source of relativistic electrons has been developed in our Terawatt Ultrafast High Field Facility (TUHFF). The preliminary results for ultrafast radiolysis of liquid water using this femtosecond electron source are presented. A TUHFF based femtosecond x-ray source is proposed. Thomson scattering of the accelerated electrons off a counterpropagating terawatt laser beam will be used to generate keV x-ray photons. The expected parameters of this x-ray source have been estimated. The short pulse duration, high flux, and good collimation of the resulting x-ray beam would be conducive for ultrafast time-resolved x-ray absorption studies of short-lived transient species in gases, liquids, and solids. It is argued that the solvation dynamics of Br atoms generated in photoinduced electron detachment from aqueous bromide would make a convenient choice for the first pump-probe experiment using this x-ray source.
The temporal structure and phase evolutions of a high-gain, self-amplified free-electron laser are measured, including single-shot analysis and statistics over an ensemble of many shots. Excellent agreement with the theory of free-electron laser (FEL) and photon statistics is found. This is an important step towards understanding and controlling the radiation in such FEL pulses.
We propose a scheme for bright, sub-100-femtosecond x-ray radiation generation using small-angle Thomson scattering. Coupling high-brightness electron bunches with high-power ultrafast laser pulses, radiation with photon energies of 8- to 40-keV can be generated with pulse duration comparable to that of the incoming laser pulse with peak spectral brightness of approximately 10<SUP>20</SUP> photons s<SUP>-1</SUP> mm<SUP>-2</SUP> mrad<SUP>-2 per 10(superscript -3</SUP> bandwidth, close to those of the third-generation synchrotron light sources. The scheme is scalable to shorter pulse duration and high peak brightness, depending on the performance of the laser system.
The EMW at the BESSRC beam lines at the APS provides high photon flux at high energies with the capability of producing circular polarization on axis. We observe a high degree of circularly polarized x-rays at such energies. The polarization and frequency tunability of the elliptical multipole wiggler (EMW) is an ideal source for many magnetic measurements from X-ray Magnetic Circular Dichroism (XMCD) to Compton scattering experiments. We performed Compton scattering measurements to determine the polarization and photon flux at the sample as a function of the deflection parameters K<SUB>y</SUB> and K<SUB>x</SUB>. We used for our measurements a Si (220) Laue monochromator providing simultaneous photon energies at 50 keV, 100 keV and 150 keV. Magnetic Compton Profiles were determined by either switching the magnet polarity or the photon helicity. The results obtained using Fe(110) single crystals were very similar.