Soft x-ray submicron imaging detector based on point defects in LiF

Abstract

The use of lithium fluoride ͑LiF͒ crystals and films as imaging detectors for EUV and soft-x-ray radiation is discussed. The EUV or soft-x-ray radiation can generate stable color centers, emitting in the visible spectral range an intense fluorescence from the exposed areas. The high dynamic response of the material to the received dose and the atomic scale of the color centers make this detector extremely interesting for imaging at a spatial resolution which can be much smaller than the light wavelength. Experimental results of contact microscopy imaging of test meshes demonstrate a resolution of the order of 400 nm. This high spatial resolution has been obtained in a wide field of view, up to several mm 2 . Images obtained on different biological samples, as well as an investigation of a soft x-ray laser beam are presented. The behavior of the generated color centers density as a function of the deposited x-ray dose and the advantages of this new diagnostic technique for both coherent and noncoherent EUV sources, compared with CCDs detectors, photographic films, and photoresists are discussed.

Using LiF crystals for high-performance neutron imaging with micron-scale resolution

“…However, it is expected that this sensitivity will be improved by ∼13 times if we use enriched 6 LiF in place of natural LiF. The sensitivity could be further improved by using polycrystalline LiF, since poly-crystalline LiF coating has proved to have ∼10 times higher sensitivity than LiF single crystal without degrading the resolution in soft x-ray imaging [16] .…”

“…In such a case, the intensity of the thermonuclear neutron source should be very high for practical applications of LiF imaging detectors. Meanwhile, in recent National Ignition Facility (NIF) experiments [39] the fast neutron yield has reached the enormous value of ∼10 16 neutrons per shot, and should be even higher in future experiments. This means that in future experiments when neutron generation reaches ∼10 17 neutrons per shot, we could expect 8 A.…”

“…Using such propagation ranges it is possible to estimate that the α and 3 H particles will deposit energy of approximately 140 and 33 eV in each lattice cell of the LiF crystal, respectively. In LiF, the F centers are created by excitation of valence electrons to the conduction band with an excitation energy [15,16] of 14 eV. It follows that the energy deposited by the α particles is sufficient to create many (∼10) F centers simultaneously in each lattice, leading to efficient formation of the F 3+ and F 2 CCs (Figure 2).…”

“…Such CCs could be hosted in LiF at room temperature for a very long time and then under excitation by UV radiation the CCs would emit photoluminescence (PL) in the visible spectral range and allow submicron spatial resolution to be reached for soft x-ray imaging when the penetration depth of the photons is on the scale of tens or hundreds of nanometers. Recently, LiF crystal and film detectors have been successfully used for high-performance soft x-ray conventional and phase-contrast imaging [16][17][18][19][20][21][22] of different nanofoils or biological objects. They have also started to be widely used for characterization intensity profiles or focusing properties of x-ray laser or high-order harmonic beams [23][24][25][26][27][28][29][30] .…”

Classical Monte-Carlo simulations of x-ray induced electron cascades in various materials

“…There are a few techniques aiming at it, e.g., utilizing FEL-induced defects (color centers) in alkali halides for spatial characterization of the pulse. 12,13 Formation of such temporally stable point defects may allow to extract pulse shape information in post-mortem measurements.…”