Ultrashort X-ray pulse science
- Univ. of California, Berkeley, CA (US). Dept. of Physics; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
A variety of phenomena involves atomic motion on the femtosecond time-scale. These phenomena have been studied using ultrashort optical pulses, which indirectly probe atomic positions through changes in optical properties. Because x-rays can more directly probe atomic positions, ultrashort x-ray pulses are better suited for the study of ultrafast structural dynamics. One approach towards generating ultrashort x-ray pulses is by 90° Thomson scattering between terawatt laser pulses and relativistic electrons. Using this technique, the author generated ~ 300 fs, 30 keV (0.4 Å) x-ray pulses. These x-ray pulses are absolutely synchronized with ultrashort laser pulses, allowing femtosecond optical pump/x-ray probe experiments to be performed. Using the right-angle Thomson scattering x-ray source, the author performed time-resolved x-ray diffraction studies of laser-perturbated InSb. These experiments revealed a delayed onset of lattice expansion. This delay is due to the energy relaxation from a dense electron-hole plasma to the lattice. The dense electron-hole plasma first undergoes Auger recombination, which reduces the carrier concentration while maintaining energy content. Longitudinal-optic (LO) phonon emission then couples energy to the lattice. LO phonon decay into acoustic phonons, and acoustic phonon propagation then causes the growth of a thermally expanded layer. Source characterization is instrumental in utilizing ultrashort x-ray pulses in time-resolved x-ray spectroscopies. By measurement of the electron beam diameter at the generation point, the pulse duration of the Thomson scattered x-rays is determined. Analysis of the Thomson scattered x-ray beam properties also provides a novel means of electron bunch characterization. Although the pulse duration is inferred for the Thomson scattering x-ray source, direct measurement is required for other x-ray pulse sources. A method based on the laser-assisted photoelectric effect (LAPE) has been demonstrated as a means of measuring ultrashort x-ray pulse durations. LAPE may also serve as the basis for a gated x-ray detector.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 666159
- Report Number(s):
- LBNL-42044; ON: DE98058305; CNN: Grant NSF PHY-9512693; TRN: US0407070
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); Supercedes report DE98058305; DN: Thesis submitted to Univ. of California, Berkeley, CA (US)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
43 PARTICLE ACCELERATORS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ACOUSTICS
DECAY
OPTICAL PROPERTIES
PHONONS
PHOTOELECTRIC EFFECT
PROBES
RECOMBINATION
RELAXATION
SOLID-STATE PLASMA
THOMSON SCATTERING
X-RAY DIFFRACTION
X-RAY SOURCES
DESIGN
LASER RADIATION
ELECTRON BEAMS
INDIUM ANTIMONIDES
X-RAY SPECTROSCOPY
LINEAR ACCELERATORS
DIAGNOSTIC TECHNIQUES