Real-Time Imaging Using a High-Power Monochromatic Terahertz Source: Comparative Description of Imaging Techniques with Examples of Application

Abstract

Gradually appearing high-power terahertz sources require the development of adequate imaging techniques. This paper describes four imaging techniques (with a thermal recorder, temperature-sensitive phosphor plates, a visible-light thermal sensitive Fizeau interferometer, and an uncooled microbolometer array) applied with the Novosibirsk terahertz free electron laser as a radiation source. The space and time resolutions of the devices were examined thoroughly. Examples of the application of these techniques, including in-line holography and real-time moving-objects detection, are given.

Review of Terahertz Tomography Techniques

“…For example, the source could be a quantum cascade laser [72], Gunn diode [73], plasma wave transistor [74,75], Backward Wave Oscillator [76], and this list in non exhaustive. We also notice the use of high power sources [77], CW gas laser [78], coherent or incoherent detectors and any combination of all these devices [79]. Moreover, a lot of new techniques have emerged such as polarization imaging [80] dark-field imaging [81], single-pixel imaging [82][83][84] and compressive imaging technique [85], real time imaging [86], time reversal imaging [87], terahertz microscope [88,89] and interferometric imaging [90,91].…”

Novosibirsk Free Electron Laser—Facility Description and Recent Experiments

“…A limited number of substances are suitable for use as "optical quality" transparent materials in the terahertz range. High-numerical-aperture kinoform lenses [10] made of high-density polypropylene 0.8 mm thick, which turned out to be resistant to intense THz radiation, enabled obtaining images with a diffraction-limited resolution [11]. Another radiation-resistant material, high-resistivity silicon, has better mechanical characteristics and many technological processes can be applied to its treatment.…”

Classical Holography in the Terahertz Range: Recording and Reconstruction Techniques

“…In case of our recorders . Then the applicability limit for the RSC reconstruction method is as follows [51]: (18) That for the angular spectrum method is (19) For calculation of the limits (Fig. 5) we used the MBA and TSPP parameters given in Section II.…”

“…In case of MBA we take the actual size as the "pixel" size, while in indirect measurements with TSPP the effective pixel size must be the spatial resolution determined by the thermal conductivity, which exceeds the wavelength. Therefore, in the latter case we may use (18) and (19), and the AS method can be applied for the object reconstruction (Fig. 5, areas 1 and 2).…”

“…When we record holograms with an MBA, the pixel size of which is less than the wavelength, (18) and (19) are not valid, because the minimum resolved size now differs from . How can (20) be adapted to a case when ?…”