We compare micromachining results with Gaussian and Bessel beams using an UV picosecond laser system and demonstrate feasibility to produce tungsten gratings for x-ray interferometry medical imaging, and sub-micrometer size hole patterns. The advantages of Bessel beams compared to Gaussian beams, are demonstrated for micromachining of rectangular shallow profile gratings with sharp edges.
The high-aspect ratio grating 10 microns wide and microns deep from tungsten foil could only be obtained with the Gaussian beam and focusing with an F-Theta type lens. Bessel beams contain significant amount of energy in the side lobes in comparison with the central peak.
The limited amount of the pulse energy in the central, 2-micron peak of the beam and destruction of the Bessel beam structure due to the narrow slit clipping the side lobes, prevented the Bessel beam deeper penetration.
On the other hand, the axicon lens and the Bessel beam shape enable creation of shallow sub-micron size structures. Traditionally, for more than years, the x-ray imaging was limited to absorption contrast. It has been proven to work very well for imaging of bones and teeth. However, absorption x-ray imaging of soft tissues requires rather high doses deposited to the patient to obtain a reasonable contrast.
Grating interferometry GI [ 1 β 3 ] is a novel imaging technique that has the potential to revolutionize medical imaging. Using advanced x-ray optics, GI records three complementary signals in a single acquisition: the absorption image, the differential phase contrast image, and the scattering image. The resulting rich contrast mechanisms provide additional information to improve diagnostic contents, yet decreasing the dose deposited to the patients, which opens new opportunities for medical imaging.
