Abstract
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 200 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.
Highlights
For more than 100 years, the x-ray imaging was limited to absorption contrast
For verifications of the Bessel beam creation and measurement method, we present on the left a wider Bessel beam with main peak Full Width Half Maximum (FWHM) about 40 microns, obtained with an axicon lens with basis angle 0.5°, which is sampled well and demonstrates the typical Bessel beam profile with side lobes
Due to imperfections of the axicon lens, our Bessel beam main peak FWHM is wider than 1 micron, and from sharpness of edges of our micromachined 10 microns wide slit, we estimate that our Bessel beam main peak FWHM is approximately 2 microns
Summary
For more than 100 years, the x-ray imaging was limited to absorption contrast. Absorption x-ray imaging of soft tissues requires rather high doses deposited to the patient to obtain a reasonable contrast. Grating interferometry (GI) [1–3] is a novel imaging technique that has the potential to revolutionize medical imaging. 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. While GI method was extensively developed in the last decade, the bottleneck for implementation of the method into real world clinics remains reliable production of gratings and their high cost of production. We aim to develop reliable gratings fabrication method with large area scalability and cost reduction perspectives
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