Three-dimensional XUV and X imaging.

XUV to X radiation has characteristics that make it particularly attractive for imaging and in particular 3-dimensional imaging. On the one hand, the short wavelength (0.01 nm to 50 nm typically) improves the spatial resolution compared to visible imaging by greatly reducing the diffraction limit. On the other hand, for wavelengths less than 1nm typically, matter begins to become transparent, whatever its nature. It should be noted that there is a reduced spectral range, between 2.2 and 4.4 nm, for which the water is transparent while the carbon is still absorbent. This so-called “water” spectral window makes it possible to produce images of biological cells with high contrast. The transparency of matter paves the way for non-destructive 3-dimensional (3D) imaging. Finally, in a manner equivalent to the reduction of the diffraction limit, XUV and X radiation makes it possible to achieve pulse durations shorter than in the visible, typically attosecond (1 as = 10-18 s) and potentially zeptosecond (1 zs = 10-21 s). In this perspective, for several years, we have been studying new schematics of XUV and X in 3D and ultra-fast.

XUV Holography and XUV Diffraction: High order harmonics as well as injected XUV lasers are sources with very high degrees of spatial coherence. High order harmonics have also demonstrated the possibility of producing attosecond pulses.

In 2006, we performed one of the first demonstration of holography performed with a beam of high order harmonics [A. S. Morlens et al., Optics Letters, 31, 21, pp. 3095-3097 (2006)]

In 2013, we investigated the impact of wavefront faults from the source of high order harmonics on the quality of an XUV diffraction image. [X. Ge et al, Optics Express, 21, 9, pp.11441-11447 (2013)]

In 2015, we performed the first holography experiment with a beam containing an attosecond pulse train. [G. Williams et al., Optics Letters 40, 13, 3205-3208 (2015)]

X-ray tomography: The reference technique in 3-dimensional X-ray imaging is still X-ray tomography, more commonly known as a scanner. Conventional algorithms for processing raw tomography data do not allow separating the real part from the imaginary part of the refractive index. However, each of these parts contains specific information about the material being probed. It is therefore interesting to be able to measure them separately.

In 2018, we performed X-ray tomography experiments to estimate the distribution of radiosensitizing nanoparticles in healthy and tumor tissues of mice. [E. Longo et al., Journal of Instrumentation, 13 (2018)] [X. Le Guevel, Nanoscale, 39, 18657-18664 (2018)]

Left: Coronal view of a mouse brain with tumors (gioblastoma), framed in yellow. Right, 3D image of a mouse tumor injected with nanoparticles containing gadolinium. The whiter the image, the higher the density of Gd.

In 2020, we began to digitally and experimentally investigate the possibility of using an x-ray wavefront sensor to simultaneously but independently measure the real and imaginary parts of the optical index of samples.

XUV and X plenoptics: X-ray tomography is a very powerful optical technique for making 3D images without having to section the sample. However, a good quality tomography requires several thousand exposures, that is, the collection of 2D images acquired from a wide variety of angles. The price to pay is a very high dose of X-rays deposited in the living or inert sample as well as a long exposure time. In 2016, we received European FET-Open funding to collaborate with five other laboratories and a company on the transposition of the so-called plenoptic technique from visible to X-rays. The plenoptic consists of coupling a wavefront sensor ( here a matrix of lenses) with imaging optics in order to achieve a very large number of images of the same object in one acquisition. By digital processing, one can create a set of images focused at different distances, just as one does physically using a zoom. From this set, we can reconstruct the object in 3D.

In 2019, we investigated the variation in contrast in digitally refocused images as a classic parameter to assess whether an object is in focus or out of focus. [VS. Herzog et al, Optics Letters, 2019]. We also carried out the first demonstration of an X plenoptic camera (at 11 keV). The article is in the process of being submitted.

In 2020, we investigated the correspondence between plenoptic and limited viewing angles tomography. [NOT. Vigano et al, J. Imaging, 6, 12 (2020)]. We also studied numerically the quality of the images formed by Fresnel X lenses having very few features. These are very special lenses that are used in the plenoptic camera’s X lens array.