P.Martin Mateos Development of an active Terahertz spectro imaging system

Development of an active terahertz spectro-imaging system

Farid Ullah Khan, and Pedro Martín Mateos Universidad Carlos III de Madrid, 28911 Leganés, Madrid, Spain

Abstract— The presentation will describe the basics and the initial steps towards the development of a novel hyperspectral imaging set-up in the terahertz. Applications of the system in the biomedical and the agri-food industry, in which terahertz spectroscopy has already demonstrated very interesting features, will be discussed.

I. INTRODUCTION AND DESCRIPTION OF THE SYSTEM

CURRENT hyperspectral terahertz imagers need to perform either a frequency or a spatial scanning, strongly restricting acquisition times and therefore the possibilities for most practical applications. We propose a novel approach based on a sophisticated dual-comb terahertz radiation source that illuminates the target area enabling the direct characterization of the spectral response of a sample simultaneously at every pixel of the image and at a rate that is orders of magnitude faster than any other comparable system.

The system is based on an electro-optic terahertz dual-comb generator providing absolute frequency accuracy, and freely adjustable resolution that results on an absolute flexibility in the configuration of the frequency range of interest and the number of frequencies to analyze. The method presented here takes advantage of the inherently high mutual coherence between individual combs on an electro-optic dual-comb source. This allows intermode beat note linewidths in the mHz providing a virtually unlimited compression on the downshifted comb lines in the RF spectrum. Hence, all the teeth of the combs can be mapped to very low frequencies, making it possible to directly detect the interference between combs by a camera (with a suitable optical/frequency range) capable of operating at a few tens of frames per second.

The set-up of the illumination system, similar to that described in [1], is shown in Fig. 1.

This illumination signal enables a fully multiplex approach in which the low-frequency interferograms are detected by all the pixels of the camera synchronously to provide simultaneous spectral and spatial characterization.

II. APPLICATIONS

In the terahertz range there are already cameras of up to 0.1 megapixels available [2] enabling fast imaging of terahertz waves. These devices operating in conjunction with the terahertz source presented above provide the strong possibility of revolutionizing nondestructive testing, quality classification and inspection in food, agricultural and pharmaceutical industries. In the same way, and equally important, the accuracy that the system proposed provides could be vital for ensuring the consistency in the study of complex biological samples, molecules and cells. To this respect, many important steps have already been taken [2, 3].

Fig. 1 Block diagram of the illumination system. REFERENCES

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[3]P. H. Siegel, IEEE Trans. Microw. Theory Tech. 52, 2438–2447 (2004).

[4] R. I. Stantchev, J. C. Mansfield, R. S. Edginton, P. Hobson, F. Palombo, and E. Hendry, Sci. Rep. 8, 6924 (2018).