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Soft x-ray submicron imaging detector based on point defects in LiF
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Image of FIG. 1.
FIG. 1.

(a) F-type CCs in alkali halide crystals. If one electron replaces an anion vacancy generated by ionizing radiation, a primary F-center is created. If two primary F centers aggregate, an color center is obtained; (b) If in a three aggregated primary centers (that is an color center) one electron is missed, the center is called .

Image of FIG. 2.
FIG. 2.

Normalized absorption (top) and emission (bottom) bands of and color centers in LiF at RT.

Image of FIG. 3.
FIG. 3.

Principle of LiF detector operation: (a) first step-irradiation of LiF by soft x-ray beam (above in case of the LPP radiation and below in case of direct x-ray beam); (b) second step-readout process of the irradiated LiF samples by optical microscope operating in the fluorescence mode.

Image of FIG. 4.
FIG. 4.

Photoluminescence spectra at RT of a LiF crystal and a thick polycrystalline LiF film, both exposed to EUV and soft x-rays at the same irradiation conditions.

Image of FIG. 5.
FIG. 5.

LiF film sample exposed to approximately 9000 shots at from the XeCl laser-plasma soft-x-ray source through a Al filter (transmitting in the EUV spectral range), followed by a polypropylene step-shaped filter; a fluence of is reached on the open area of the film, while a fluence zero is corresponding to the completely closed area of the film. The sample is observed in fluorescence mode by exciting at with an ion Ar laser, and observing by a low magnification microscope through a yellow filter.

Image of FIG. 6.
FIG. 6.

F center density in LiF crystal as a function of the soft-x-ray irradiation doses at a dose rate : the experimental data (dots) are well fitted by Eq. (1) for and .

Image of FIG. 7.
FIG. 7.

(a) Image of grids (the diameter of the circles is , the period is , the thickness of the wires is ) on a LiF crystal, observed with an optical microscope in fluorescence mode with a objective. The grids were placed in contact with the LiF crystal and irradiated by soft-x-ray radiation, created by interaction of the XeCl laser with a Fe target, in 1000 shots; (b) enlarged part of the image, observed with a Nikon microscope with a objective; the densitogram of the image shows a spatial resolution value close to the spatial resolution limit of the microscope.

Image of FIG. 8.
FIG. 8.

(a) Image of a grid placed in contact with a LiF crystal during the exposure to soft x-rays; the LiF is observed with an optical microscope in fluorescence mode with a objective; (b), (c) enlarged parts of the grid image, observed with a Leica confocal microscope with a and objective, respectively; (d) densitogram of the image showing a submicron spatial resolution.

Image of FIG. 9.
FIG. 9.

(a) Image of a grid placed in contact to a LiF crystal during the exposure to a single shot x-ray radiation emitted by the Nd:glass laser-plasma source with a Cu target, observed with a confocal microscope in fluorescence mode with a objective; (b) Enlarged part of the image (a), observed with the same microscope under magnification , and densitogram of the image, which shows a submicron spatial resolution.

Image of FIG. 10.
FIG. 10.

Result of the exposure of a LiF film (above) and a PMMA photoresist (below) at same irradiance conditions through a step-shaped polypropylene phantom which reduced the x-ray fluence by a factor 1 (area “a”), 150 (area “b”), 300 (area “c”), and 600 (area “d”).

Image of FIG. 11.
FIG. 11.

(a) Image of a dragonfly wing obtained on a LiF film and observed under a conventional fluorescence microscope with a objective; (b) and (c) enlarged areas of the image (a), observed under a conventional optical microscope with a objective and under a Leica confocal microscope with a objective, respectively. The densitograms under the images show that the observed spatial resolution is strongly depending from the resolution limit of the used microscope, and that the really reached spatial resolution is not worse than . (d) Image of the twin wing (of the same dragonfly sample) on a PMMA photoresist, obtained at the same experimental conditions. Note the much poorer dynamical range of PMMA compared with LiF.

Image of FIG. 12.
FIG. 12.

Image of a mosquito wing, obtained by contact radiography on a LiF crystal, and observed under a Zeiss LSM 510 fluorescence confocal optical microscope with a objective with different zooming ratios. The densitogram shows the size of a rib, but the small hairs, which have a thickness , are also very well resolved on the whole surface.

Image of FIG. 13.
FIG. 13.

Observation of the quasi-near-field x-ray laser beam intensity distribution emitted by a Ne-like Ar capillary discharge at . (a) Conjugate image of the beam at the output of the capillary channel, obtained on a LiF film detector with a demagnification by a focusing multilayer mirror, , obtained with a single laser shot for an initial Ar-gas pressure of and a long capillary. (b) Image of the same laser beam, obtained with the same experimental conditions as in (a), but after shifting the LiF detector by out of the mirror conjugate position. The images show changes in the beam intensity distribution at tiny details. (c) A 1:1 conjugate image of the beam profile at the output of the capillary channel, obtained using two focal length mirrors and a conventional coupled system composed by and a phosphor screen.

Image of FIG. 14.
FIG. 14.

(a) Observation of the quasi-far-field spatial intensity distribution of the Ne-like Ar capillary discharged x-ray laser beam (circular structure in the image), passing through a Al filter (supported by a Ni mesh) and stored on a LiF film detector placed at a distance of from the capillary exit; in the image, the interference patterns generated by the Ni mesh (period , wire thickness ) through the gap between the mesh and the detector are clearly visible (the bar corresponds to an angle of ); (b) Densitogram of the image (a); (c) Detail of the patterned image and it densitograms in the two perpendicular directions, showing the scale oscillation of the intensity due to the diffraction effect.

Image of FIG. 15.
FIG. 15.

(a) Image of interference patterns (detail) on LiF and its densitogram. The image was observed with an optical microscope (ZEISS Axioplan 2), operating in fluorescence mode with magnification. Plot profile demonstrates a spatial resolution of (limit of the optical microscope). (b) Scheme of the related experimental setup.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Soft x-ray submicron imaging detector based on point defects in LiF