Laser X-ray

For many problems in atomic, molecular and solid-state physics intense sources of tunable X-rays are required. Examples are inner-shell excitation of atoms and molecules or the spectroscopy on multiply-charged ions. Up to now these demands could only be met partly by X-ray tubes or by syn- 

Such soft X-ray lasers have meanwhile been realized [5.246-251]. The shortest wavelength reported so far is 6 nm [5.250]. More detailed information on this interesting subject can be found in [5.249-254]. 

For many problems in atomic, molecular, and solid-state physics intense sources of mnable X-rays are required. Examples are inner-shell excitation of atoms and molecules or spectroscopy of multiply charged ions. Until now, these demands could only partly be met by X-ray tobes or by synchrotron radiation. The development of lasers in the spectral range below 100 nm is therefore of great interest. Besides the free electton laser, which represents the most powerful but expensive X-ray laser, there are other possibilities which can realize much less expensive table top lasers in the X-ray region. They are based on different excitation mechanisms  

An example of X-ray amplification in nickel-like palladium Pd is shown in Fig. 5.110, where a terawatt laser pulse created a hot plasma from a palladium surface. By recombining electrons with highly charged palladium ions, inversion between two Rydberg states of Pd + could be achieved, resulting in an intense laser line at A = 14.7 nm [508, 509]. 

An efficient way to generate inversion is to use double pulses [510], where the first pulse heats and explodes a thin metal foil, producing a hot plasma. The second pulse further ionizes the plasma, generating highly charged ions, which can recombine with electrons creating inversion between two Rydberg levels (Fig. 5.111). 

Such soft X-ray lasers have already been realized [511-514], The shortest wavelength reported to date is 6 nm [513], Resonators for X-ray lasers can be composed of Bragg reflectors, which consist of suitable crystals that can be tilted to fulfill the Bragg condition sin i) = w A for constructive interference between the partial waves reflected by the crystal planes with distance d (Fig. 5.109b). 

According to (2.22), the spontaneous transition probability A/ scales with the third power of the emitted frequency. The losses of upper-state population N( by fluorescence are therefore proportional to Aihv a y This means 

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Yoo C S, Akella J and Nicol M 1996 Chemistry at high pressures and temperatures in-situ synthesis and characterization of p-SijN by DAC x-ray/laser-heating studies Advanced Materials 96 ed M Akaishi et al (Tsukuba National Institute for Research in Inorganic Materials) p 175... 

The development of mote intense sources (eg, plasma sources, soft x-ray lasers, and synchrotron sources) has made possible highly effective instmments both for x-ray microscopy and x-ray diffraction on a few cubic nanometer sample. The optical problem of focusing x-rays is accompHshed by the use of zone plates or by improved grazing incidence or multilayer reflectors. 

Lasers act as sources and sometimes as amplifiers of coherent k—uv radiation. Excitation in lasers is provided by external particle or photon pump sources. The high energy densities requked to create inverted populations often involve plasma formation. Certain plasmas, eg, cadmium, are produced by small electric discharges, which act as laser sources and amplifiers (77). Efforts that were dkected to the improvement of the energy conversion efficiencies at longer wavelengths and the demonstration of an x-ray laser in plasma media were successful (78). 

AU information inclnded in this snmmary was snpplied by the vendor and has not been independently verified. The technology is predicated npon the existence of a tnnable X-ray laser. The cnrrent state-of-the-art in this area snggests that, at best, the availability of the technology is many years in the fntnre. 

Unfortunately, the experimental data cannot be correlated directly with the crystal structure, because some of the information needed is lost in recording the X-ray intensity pattern. Indeed, the diffracted X-ray beam is a vector, and it has both an intensity and a phase angle. The information concerning phase angle is lost during measurement of the X-ray intensity. The phase angle could, perhaps, be recorded by a holographic method, but X-ray lasers do not as yet exist. 

Extensive development and experimental designs of stilt x-ray lasers have been underway al the Lawrence Livermore National Laboratory and the Princeton Plasma Physics Laboratory, among other research institutions. 

These advances have opened new fields of relativity-related research in two complementary directions. One is related to the advent of laser-based sources of coherent radiation in the X-UV domain, either from high harmonic generation [6], [7] or from X-ray-laser devices, [8], The imple-... 

We have considered in particular the case of multiphoton transitions, to be observed with the help of intense high frequency fields as produced by X-ray Lasers or Free-Electron Lasers (FEL). As a result of our analysis, we have shown that two-photon bound-bound transition amplitudes in high-Z hydrogenic systems are significantly affected by relativistic corrections, even for low values of the charge of the nucleus. For instance at Z = 20, the corrections amount to about 10%, a value much higher than what is observed for standard one-photon transitions in X-ray spectroscopy measurements for which the non-relativistic dipole (NRD) approximation agrees with the exact result to within 99% at comparable frequencies. 

Recent references can be found in X-Ray Lasers 1996, Institute of Physics Conferences Series 151, (1996). 

H.N. Chapman et al., Femtosecond X-ray protein nanocrystallography, Nature 470 (2011) 73 M.M. Seibert et al., Single mimivirus particles intercepted and imaged with an X-ray laser, Nature 470 (2011) 78. 

U. Saahnann, J.M. Rost, Ionization of clusters in strong X-ray laser pulses, Phys. Rev. Lett. 89 (2002) 143401. 

L. Young et al., Femtosecond electronic response of atoms to ultra-intense X-rays, Nature 466 (2010) 56 J. Wark, Atomic physics X-ray laser peels and cores atoms, Nature 466 (2010) 35. 

Lawrence, J. R., Swerhone, G. D. W., Leppard, G. G., Araki,T., Zhang, X., West, M. M., and Hitchcock, A. P. (2003). Scanning transmission X-ray, laser scanning, and transmission electron microscopy mapping of the exopolymeric matrix of microbial biofilms. Appl. Environ. Microbiol. 69,5543-5554. 

Hydrogen and other one-electron atoms can be made into lasers because the state lifetimes vary so greatly. For example, an X-ray laser can be built by blasting carbon rods with an intense field, stripping off all the electrons. When the first electrons recombine with the nuclei, one-electron C5+ atoms are created in a wide variety of stationary states. Any population in the 2p states rapidly decays to the ground state population in 3s or 3 d decays more slowly. Thus the 3s —> 2p and 3d —> 2p transitions develop an inverted population distribution, and lase at the energy difference between the two states (A, = 13.6 nm). 

One kind of X-ray lasers is a subcase of the so-called free electron laser. Electrons, accelerated are forced, to almost the speed of light ("relativistic electrons") by klystrons and then bent or wiggled in special magnets called undulators are forced to emit some of their energy as synchrotron radiation inside the undulator, the synchrotron pulses can induce in-phase synchrotron emission by other electrons, thus producing a pulse at X-ray wavelengths. This was recently demonstrated as almost possible (2009). 

A second, older type of X-ray laser uses a powerful Nd-YAG pumping laser (e.g., Nova) to excite plasmas (e.g., Ne-like Ti+12 ions), which in turn can emit soft X rays by now even tabletop soft X-ray lasers exist (using the chirped-amplification of a Nd YAG laser fired once every 3 to 4 minutes, and Ni-like Pd1 4 ions). 

An X-ray laser (powered by a thermonuclear explosion) was proposed in the 1980s as a military "death ray" its single underground test in 1983 was inconclusive, and its research was stopped. 

Nnhn H, Rossbach J (2000) LINAC-based short wavelength FELs The challenges to be overcome to produce the nltimate X-ray source-the X-ray laser. Synchrot Radial News 13 18-32 OTfare D, Evans ISO, Francis R, Price S, O Brien S (1998a) The use of in situ powder diffraction in the study of intercalation and hydrothermal reaction kinetics. Mater Sci Forum 278 367-378 OHare D, Evans ISO, Francis RJ, Halasyamani PS, Norby P, Hanson J (1998b) Time-resolved, in situ X-ray diffraction studies of the hydrothermal syntheses of microporous materials. Microporous Mesoporous Mat 21 253-262... 

In general there are two lithographic processes used in computer-circuit fabrication -photolithography and radiation (X-ray, laser, electron-beam and deep-UV (248- and 193-nm wavelength)) lithography. The principal difference is the radiation source and wavelength, which in turn define the feature size which can be achieved. 

X-ray laser pumping, especially optical-field-ionisation pumping... 

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