Ultrafast laser generation of hard x-rays
This dissertation describes the efficient production of hard x-rays from a laser-produced plasma, and the construction of the driving laser. More than 0.3% of the incident laser energy is converted to x-radiation between 20 and 300 keV, although the spectrum extends beyond 1 MeV. These results are obtained by focusing a 60 mJ, 120 fsec, 807 nm laser, operated at a 5 Hz repetition rate, to greater than 10{sup 18} W/cm{sup 2} onto a solid tantalum target. The x-ray spectrum is determined by measuring the transmission of various metal filters, using a calibrated 25 mm NaI detector as a calorimeter. This data is well fit by assuming that the x-ray spectral distribution is described by a 1/energy function. By limiting the solid angle collected by the NaI detector to 1.2 {mu}ster and filtering the x-rays with 19 mm of lead, single photon pulse height analysis is achieved. This data indicates that the x-ray spectrum falls faster than 1/energy at high (>350 keV) photon energies, yet a characteristic temperature or spectral cut-off has not been observed. More than 100 {mu}J of hard x-rays are emitted from an expected 500 {mu}m region in less than 1 psec. Greater than 10{sup 6} photons above 1 MeV are generated with each shot. The laser technology is sufficiently economical that the x-ray source described here will become a significant laboratory tool, allowing many laboratories to use x-ray pulses that are shorter and brighter than ever before available.
- Research Organization:
- Stanford Univ., CA (United States)
- OSTI ID:
- 121152
- Country of Publication:
- United States
- Language:
- English
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