Laser-Compton scattering is a promising method for generating high-brightness, ultrashort, energy-tunable X-rays. We have developed a compact X-ray source using laser-Compton scattering. Hard X-rays, ranging from 15 keV to 34 keV, were generated with a low-emittance, 38 MeV, 0.8 nC electron accelerator and a femtosecond 4TW Ti:sapphire laser. The created X-rays were composed of 2×106 (5×105) photons/pulse for interaction angles between an electron bunch and a laser pulse of 165° (90°). A highly accurate timing synchronization scheme was employed, and the fluctuation of the generated X-rays was suppressed to 11% (rms) for the 90° scattering. The spatial (angular) distributions for the intensity and the energy of the generated X-ray were measured, and agreed well with theoretical calculations. Thus, X-ray imaging has been demonstrated using a phase-contrast technique with the interference of an X-ray beam.
We report on a diode-pumped Yb:S-FAP CPA laser system for laser-Compton X-ray generation. We obtained amplified pulse energies up to 114 mJ at a repetition rate of 50 Hz after the preamplifier in chirped-pulse amplification. We also obtained amplified pulse energies up to 0.6 J after the main amplifier in preliminary long-pulse experiments.
Timing synchronization between two independent Ti:sapphire mode-locked lasers has been developed for Laser-Compton X-ray generation. The lasers operated at different repletion frequencies of 119 MHz and 2856 MHz. The two lasers were actively synchronized with a phase-locked loop at a frequency of 2856 MHz. Fluctuation of the optical sum-frequency intensity was measured, and timing jitter was obtained. The rms timing jitter between the lasers was below 5 fs for several tens of seconds. The fluctuation was measured with a maximum observation bandwidth of 300 kHz. To improve long-time stability, a sum-frequency signal was fed back with a slow loop bandwidth, achieving long time operation for 1 hour with 5 fs synchronization.
FESTA has been developing short pulse X-ray generation technologies using Laser-Compton scattering. Two years ago, X-ray generation with a 90-degree collision configuration was achieved using a photocathode as the electron source and a 100fs Ti:sapphire laser as the photon source. Electron and laser light pulses were synchronized so that the fluctuation of X-ray intensity was 25% (rms). In the next stage, the x-ray generation system is being modified for use in practical applications. The electron energy has been raised to 40 MeV to increase to X-ray photon energy. Laser power will be increased to 0.5 J/pulse with a 100Hz repetition rate. The laser gain medium has been changed to Yb:S-FAP which is pumped by laser diodes. The synchronization system will be further modified to increase its stability. These technologies will be used to generate 15 -to 30 keV X-ray pulses with a stable peak-to-peak intensity for use in several applications.
We have developed a stable 7 terawatt (TW) (168 mJ per pulse, 24 fs pulse duration) Ti: sapphire laser system operating at 50 Hz for a generation of femtosecond X-ray pulses by inverse Compton scattering. We corrected the wavefront distortion of these high intensity laser pulses with adaptive optics using a Shack-Hartmann type wavefront sensor and a deformable mirror. We have also started developing a compact all-solid-state Yb: Sr5(PO4)3F (Yb: S-FAP) laser system to realize a practical X-ray pulse generation system. We measured thermal lensing induced in Yb: S-FAP crystal for design of a high-energy regenerative amplifier. In addition, we measured wavefront of the amplified pulses in the Yb:
S-FAP regenerative amplifier with the wavefront sensor.
We demonstrated generation of square-shaped ultraviolet pulses and that they reduces the emittance of electron beams from laser-photocathode RF-gun. Some frequency components of femtosecond pulses from a Ti:sapphire oscillator are modulated with a pulse shaper that consists of a lens pair, gratings, and a liquid crystal spatial light modulator (LC-SLM) to generate square-shaped pulses. The shaped pulses were amplified up to 3 mJ through a regenerative amplifier, and were converted to ultraviolet region with two different nonlinear crystals. Energy of the shaped pulses was about 100 (mu) J which is sufficient to generate electron charge of 1 nC. In our experiment, emittance of electron beam was reduced to as low as almost the half of that with non-shaped pulses.
We report on the recent progress of a compact laser Compton monochromatic X-ray source based on the inverse Compton scattering of 100mJ, 100 femtosecond laser pulses by 13MeV, 3 picosecond, InC electron bunches. Experimental results are reviewed on the 4.6keV, 3 picosecond and 2.3keV, 300 femtosecond X-ray pulses.
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