Abstract
Medical and many other applications require small-volume setups enabling terahertz imaging. Therefore, we aim to develop a device for the in-reflection examination of the samples. Thus, in this article, we focus on the diffractive elements for efficient redirection and focusing of the THz radiation. A terahertz diffractive optical structure has been designed, optimized, manufactured (using extrusion-based 3D printing) and tested. Two manufacturing methods have been used—direct printing of the structures from PA12, and casting of the paraffin structures out of 3D-printed molds. Also, the limitations of the off-axis focusing have been discussed. To increase the efficiency, an iterative algorithm has been proposed that optimizes off-axis structures to focus the radiation into small focal spots located far from the optical axis, at an angle of more than 30 degrees. Moreover, the application of higher-order kinoform structure design allowed the maintaining of the smallest details of the manufactured optical element, using 3D printing techniques.
Highlights
The terahertz radiation spectrum has been at the center of researchers’ attention for the last few decades [1] due to its specific features
The two designed diffractive optical elements are working in transmission and are redirecting the incident radiation off-axis and focus the beam at a particular distance
The structure needs to be thin and light with short focal length, which allows focusing of THz radiation into a small focal spot located outside the contours of the device
Summary
The terahertz radiation spectrum has been at the center of researchers’ attention for the last few decades [1] due to its specific features. These features comprise non-invasiveness [2,3,4] and non-ionization as well as high absorption and dispersion in water [5] which is a major component of biological tissues. Our ambition is to design, manufacture and verify thin diffractive optical elements (DOEs) which would allow the development of compact and more applicable THz skin scanners. Further work aims at optimization of inspection setup by applying point-to-point lenses on both sides and reducing focal lengths further. In this article the theoretical and experimental comparison of off-axis diffractive structures for the THz spectrum
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