International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 4.2, pp. 198-199

Section 4.2.1.6. Plasma X-ray sources

U. W. Arndta

4.2.1.6. Plasma X-ray sources

| top | pdf |

Plasma sources of hard X-rays are being investigated in many laboratories. Most of the material in this section is derived from publications from the Laboratory for Laser Energetics, University of Rochester, USA. Plasma sources of very soft X-rays have been reviewed by Byer, Kuhn, Reed & Trail (1983[link]).

The peak wavelength of emission from a black-body radiator falls into the ultraviolet at about 105 K and into the X-ray region between 106 and 107 K. At these temperatures, matter is in the form of a plasma that consists of highly ionized atoms and of electrons with energies of several keV. The only successful methods of heating plasmas to temperatures in excess of 106 K is by means of high-energy laser beams with intensities of 1012 W mm−2 or more. The duration of the laser pulse must be less than 1 ns so that the plasma cannot flow away from the pulse. When the plasmas are created from elements with 15 [\lt] Z [\lt] 25, they consist mainly of ions stripped to the K shell, that is of hydrogen- and helium-like ions. The X-ray spectrum (Fig. 4.2.1.12[link] ) then contains a main group of lines with a bandwidth for the group of about 1%; the band is situated slightly below the K-absorption edge of the target material. The intensity of the band drops with increasing atomic number. For diffraction studies, Forsyth & Frankel (1980[link], 1984[link]) and Frankel & Forsyth (1979[link], 1985[link]) used a multi-stage Nd3+:glass laser (Seka, Soures, Lewis, Bunkenburg, Brown, Jacobs, Mourou & Zimmermann, 1980[link]), which was able to deliver up to 220 J per pulse of width 700 ps. They obtained [6\times10^{14}] photons pulse−1 for a Cl15+ plasma with a mean wavelength of about 4.45 Å and about [3\times10^{13}] photons pulse−1 for a Fe24+ plasma at about 1.87 Å (Yaakobi, Bourke, Conturie, Delettrez, Forsyth, Frankel, Goldman, McCrory, Seka, Soures, Burek & Deslattes, 1981[link]). More recently, the laser was fitted with a frequency conversion system that shifts the peak power of the laser light from the infrared (1.054 µm) to the ultraviolet (0.351 µm) (Seka, Soures, Lund & Craxton 1981[link]). This led to a more efficient X-ray production, which permitted a more than twofold increase in X-ray flux, even though the maximum pulse energies had to be reduced to ∼50 J to prevent damage to the optical components (Yaakobi, Boehli, Bourke, Conturie, Craxton, Delettrez, Forsyth, Frankel, Goldman, McCrory, Richardson, Seka, Shvarts & Soures, 1981[link]). Forsyth & Frankel (1984[link]) used the plasma X-ray source for diffraction studies with 4.45 Å X-rays with a focusing collimation system that delivered up to 1010 photons pulse−1 to the specimen over an area approximately 150 µm in diameter. More recently, by special target design (Forsyth, 1986, unpublished), fluxes have been increased by factors of 2 to 3 without altering the laser output. Other plasma sources have been described by Collins, Davanloo & Bowen (1986[link]) and by Rudakov, Baigarin, Kalinin, Korolev & Kumachov (1991[link]).

[Figure 4.2.1.12]

Figure 4.2.1.12 | top | pdf |

X-ray emission from various laser-produced plasmas. From Forsyth & Frankel (1980[link]); courtesy of J. M. Forsyth.

The cost of plasma sources is about an order of magnitude greater than that of rotating-anode generators (Nagel, 1980[link]). Their use is at present confined to flash-diffraction experiments, since the duty cycle is a maximum of one flash every 30 min. Attempts are being made to increase the laser repetition rate; a substantial improvement could lead to a source that would rival storage-ring sources.

References

Byer, R. L., Kuhn, K., Reed, M. & Trail, J. (1983). Progress in high peak and average power lasers for soft X-ray production. Proc. SPIE, 448, 2–7.
Collins, C. B., Davanloo, F. & Bowen, T. S. (1986). Flash X-ray source of intense nanosecond pulses produced at high repetition rates. Rev. Sci. Instrum. 57, 863–865.
Forsyth, J. M. & Frankel, R. D. (1980). Flash X-ray diffraction from biological specimens using a laser-produced plasma source. Report No. 106. Laboratory for Laser Energetics, University of Rochester, USA.
Forsyth, J. M. & Frankel, R. D. (1984). Experimental facility for nanosecond time-resolved low-angle X-ray diffraction experiments using a laser-produced plasma source. Rev. Sci. Instrum. 55, 1235–1242.
Frankel, R. D. & Forsyth, J. M. (1979). Nanosecond exposure X-ray diffraction patterns from biological specimens using a laser plasma source. Science, 204, 622–624.
Frankel, R. D. & Forsyth, J. M. (1985). Time-resolved X-ray diffraction study of photo stimulated purple membrane. Biophys. J. 47, 387–393.
Nagel, D. J. (1980). Comparison of X-ray sources for exposure of photo resists. Ann. NY Acad. Sci. 342, 235–247.
Rudakov, L. I., Baigarin, K. A., Kalinin, Y. G., Korolev, V. D. & Kumachov, M. A. (1991). Pulsed-plasma-based X-ray source and new X-ray optics. Phys. Fluids B (Plasma Phys.), 3, 2414–2419.
Seka, W., Soures, J. M., Lewis, O., Bunkenburg, J., Brown, D., Jacobs, S., Mourou, X. & Zimmermann, J. (1980). High-power phosphate-glass laser system: design and performance characteristics. Appl. Opt. 19, 409–419.
Seka, W., Soures, J. M., Lund, L. & Craxton, R. S. (1981). GDL: a high-power 0.35 µm laser irradiation facility. IEEE J. Quantum Electron. QE-17, 1689–1693.
Yaakobi, B., Boehli, T., Bourke, P., Conturie, Y., Craxton, R. S., Delettrez, J., Forsyth, J. M., Frankel, R. D., Goldman, L. M., McCrory, L. R., Richardson, M. C., Seka, W., Shvarts, D. & Soures, J. M. (1981). Characteristics of target interaction with high-power UV laser radiation. Opt. Commun. 39, 175–179.
Yaakobi, B., Bourke, P., Conturie, Y., Delettrez, J., Forsyth, J. M., Frankel, R. D., Goldman, L. M., McCrory, L. R., Seka, W., Soures, J. M., Burek, A. J. & Deslattes, R. D. (1981). High X-ray conversion efficiency with target irradiation by a frequency-tripled Nd:glass laser. Opt. Commun. 38, 196–200.








































to end of page
to top of page