Current Issue : January - March Volume : 2017 Issue Number : 1 Articles : 6 Articles
Focusing of X-rays to nanometre scale focal spots requires high precision X-ray optics. For nanofocusing\nmirrors, height errors in the mirror surface retard or advance the X-ray wavefront and after\npropagation to the focal plane, this distortion of the wavefront causes blurring of the focus resulting\nin a limit on the spatial resolution. We describe here the implementation of a method for correcting\nthe wavefront that is applied before a focusing mirror using custom-designed refracting structures\nwhich locally cancel out the wavefront distortion from the mirror. We demonstrate in measurements\non a synchrotron radiation beamline a reduction in the size of the focal spot of a characterized test\nmirror by a factor of greater than 10 times. This technique could be used to correct existing synchrotron\nbeamline focusing and nanofocusing optics providing a highly stable wavefront with low distortion\nfor obtaining smaller focus sizes. This method could also correct multilayer or focusing crystal\noptics allowing larger numerical apertures to be used in order to reduce the diffraction limited focal\nspot size...
Petawatt, picosecond laser pulses offer rich opportunities in generating synchrotron x-rays. This paper\nconcentrates on the regimes accessible with the PETAL laser, which is a part of the Laser Megajoule (LMJ)\nfacility. We explore two physically distinct scenarios through Particle-in-Cell simulations. The first one\nrealizes in a dense plasma, such that the period of electron Langmuir oscillations is much shorter than the pulse\nduration. Hallmarks of this regime are longitudinal breakup (ââ?¬Å?self-modulationââ?¬Â) of the picosecond-scale laser\npulse and excitation of a rapidly evolving broken plasma wake. It is found that electron beams with a charge of\nseveral tens of nCcan be obtained, with a quasi-Maxwellian energy distribution extending to a few-GeVlevel.\nIn the second scenario, at lower plasma densities, the pulse is shorter than the electron plasmaperiod. The pulse\nblows out plasma electrons, creating a single accelerating cavity, while injection on the density downramp\ncreates a nC quasi-monoenergetic electron bunch within the cavity. This bunch accelerates without\ndegradation beyond 1 GeV. The x-ray sources in the self-modulated regime offer a high number of photons\n(âË?¼1012) with the slowly decaying energy spectra extending beyond 60 keV. In turn, quasimonoenergetic\ncharacter of the electron beam in the blowout regime results in the synchrotron-like spectra with the critical\nenergy around 10 MeVand a number of photons> 109.Yet, much smaller source duration and transverse size\nincrease the x-ray brilliance by more than an order of magnitude against the self-modulated case, also favoring\nhigh spatial and temporal resolution in x-ray imaging. In all explored cases, accelerated electrons emit synchrotron x-rays of high brilliance, B > 1020 phot Synchrotron sources\ndriven by picosecond kilojoule lasers may thus find an application in x-ray diagnostics on such facilities such\nas the LMJ or National Ignition Facility (NIF)...
Small x-ray beam sizes necessary for probing nanoscale phenomena require exquisite stability to prevent\ndata corruption by noise. One source of instability at synchrotron radiation x-ray beamlines is the slow\ndetuning of x-ray optics to marginal alignment where the onset of clipping increases the beamâ��s\nsusceptibility to higher frequency position oscillations. In this article, we show that a 1 �¼m amplitude\nhorizontal x-ray beam oscillation driven by power line harmonic leakage into the electron storage ring can\nbe used as perturbation for horizontal position extremum seeking feedback. Feedback performance is\ncharacterized by convergence to 1.5% away from maximum intensity at optimal alignment....
We present a new planar Ni compound refractive lens for high energy X-rays (116 keV). The\nlens is composed of identical plano-concave elements with longitudinal parabolic grooves manufactured\nby a punch technique. In order to increase the lens transmission, the thickness of\nthe single lens at the parabolic groove vertex was reduced to less than 5 �¼m and the radius\nof curvature was reduced to about 20 �¼m. The small radius of curvature allowed us to reduce\nthe number of single elements needed to get the focal length of 3 m to 54 single lenses. The\ngain parameter has been significantly improved compared to the previous lenses due to higher\ntransmission, but the focused beam size and its gain are not as good as expected, mostly due\nto the aberrations caused by the lens shape imperfections....
This paper describes an application of infrared light-induced de-polarization applied on a\npolarized CdZnTe detector working under high radiation fluxes. We newly demonstrate the influence\nof a high flux of X-rays and simultaneous 1200-nm LED illumination on the spectroscopic properties\nof a CdZnTe detector. CdZnTe detectors operating under high radiation fluxes usually suffer from\nthe polarization effect, which occurs due to a screening of the internal electric field by a positive\nspace charge caused by photogenerated holes trapped at a deep level. Polarization results in the\ndegradation of detector charge collection efficiency. We studied the spectroscopic behavior of CdZnTe\nunder various X-ray fluxes ranging between 5 Ã?â?? 105 and 8 Ã?â?? 106 photons per mm2 per second. It was\nobserved that polarization occurs at an X-ray flux higher than 3Ã?â??106 mmâË?â??2Ã?·sâË?â??1. Using simultaneous\nillumination of the detector by a de-polarizing LED at 1200 nm, it was possible to recover X-ray\nspectra originally deformed by the polarization effect....
The grazing-incidence hard X-ray retro-reflector (GIRR) is a novel optical element,\nwhich completely suppresses the conventional mirror beam in the retro-reflection\nmode, and, at the same time, totally reflects the primary grazing incident X-radiation\nbackwards to its source in strictly anti-parallel direction with minimal scattering. The\nGIRR is a good alternative to hard X-ray normal-incidence Bragg mirror, and has a\nhigh potential for applications in various X-ray optical devices and techniques, such\nas, hard X-ray optical noise (or background) filters, high-quality hard X-ray waveguides,\nlow-gain hard X-ray free electron laser resonators (XFELRs), X-ray holography,\ncoherent X-ray diffraction imaging, phase-contrast imaging, as well as in hard\nX-ray optical data storage devices and deep space hard X-ray communications. The\nproposed optical element consists of single-crystal wafer covered by a thin, non-diffracting\nlayer of low-absorbing material....
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