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.
A short pulse X-ray generation experiment was performed by laser-Compton scattering through interaction between a 3 ps, 14 MeV electron beam and 100 fs, 85 mJ laser photons in a 90° scattering configuration. The observed X-ray intensity was typically 30,000 photons/pulse and roughly matched the theoretically expected intensity. The X-ray energy and pulse duration were estimated theoretically to be 2.3 keV and 280 fs from the observed electron and laser beam parameters. The pulse to pulse fluctuation of the X-ray output was measured as 25% (rms) during 30-minute operation. The fluctuation was expressed as a function of the fluctuation of the timing between the electron and laser beams. The measured fluctuation of the X-rays was approximately consistent with that caused by the fluctuation of each beam. We are improving the system to achieve the photon energy to 15 keV and the intensity to 10 million photons/pulse by increasing the electron beam energy to 40 MeV and the laser pulse energy to 1 J/pulse, and to stabilize the X-ray intensity to be better than 3% by improving the timing fluctuation between beams to be less than 300 fs. The amplitude fluctuation of each electron and laser beams are improved to be less than 1% to contribute to the achievement of the targeted 3% X-ray fluctuation.
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.
A multipass amplifier for a picosecond Nd:YLF laser was designed and developed for the light source of a laser-Compton X-ray generator. The developed amplifier was constructed of a water-cooled Nd:YLF rod (20mm long, 4mm in diameter) and a pair of quasi-CW laser diodes (peak power 1kW) with optical systems for rod pumping. The amplifier was operated as a laser with a generated output energy of 218mJ and slope efficiency of 31% at 10Hz. We then operated the laser as an amplifier with 0.4mJ, at 10ps, 1047nm seed light. The amplified energy was 4mJ in the single-pass configuration and 3OmJ in the double-pass configuration. The experiment result was compared with the theoretical result derived from the Frantz-Nodvik equation. The results agreed well in the lower energy region but diverged in the higher energy region.
A description is given in this paper on the present progress of a compact laser synchrotron femtosecond x-ray source based on the inverse Compton scattering of high energy femtosecond laser pulses by high energy electrons. The present research program is reviewed by the target energy and number of the femtosecond x-ray photons for phase 1 (1996 - 2000) and phase II (2001 - 2004). Possible examples are considered for ultrafast imaging and pump- probe experiments by using this x-ray source.
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