Experimental research on terahertz Gabor inline digital holography of concealed objects

Abstract

Terahertz (THz) radiation has the characteristics of penetrating nonmetallic and nonpolar materials that are opaque to visible light, which makes THz digital holography have an application potential of imaging concealed objects with certain barriers. A CO(2) pumped continuous THz Gabor inline digital holographic imaging system was utilized to conduct experimental researches on imaging concealed objects. Paper, Teflon, a plastic express envelope, and silicon wafers were used as barriers. High-quality reconstructed images were obtained. Compared with the reconstruction results without any barriers, the results verify the feasibility of THz Gabor inline digital holography in imaging concealed objects.

Terahertz in-line digital holography of dragonfly hindwing: amplitude and phase reconstruction at enhanced resolution by extrapolation

“…The reconstructions demonstrated a resolution of about 0.2 mm. They also verified the feasibility of THz Gabor in-line digital holography in imaging concealed objects [12]. However, no simultaneous reconstruction of absorption and phase-shifting distributions from a single terahertz in-line hologram has yet been reported.…”

“…The same researchers reported in 2012 an improved reconstruction technique: this is achieved by upsampling of the off-axis holograms and suppressing the zero-order artifact, which allowed the resolution to be improved by up to 0.245 mm [11]. In 2012, the same group demonstrated for the first time THz Gabor in-line holography using the same source and detector [12][13].…”

Surface Characterization by the Use of Digital Holography

“…Since the usual DH uses a visible light, it is difficult to visualize 3D internal structure of visibly opaque objects due to their limited penetration depth. The compelling advantage of THz radiation is that it has a good penetration capability; thus, 3D visualization of both surface shape and internal structure in visibly opaque object can be achieved [12]. We constructed off-axis THz digital holography (THz-DH) system equipped with CW-THz radiation generated by QCL, and the THz digital hologram is captured by a THz camera.…”

Application of autofocusing methods in continuous-wave terahertz in-line digital holography

“…Compared with the detectors which obtain phase and amplitude simultaneously, terahertz digital holography is a full-field phase-contrast method without scanning. In the past decade, many researchers have explored and demonstrated the imaging technology of terahertz digital holography with different schematics like millimeter-wave Fresnel offaxis digital holography [4], pulsed terahertz digital holography [5], tunable terahertz source holographic imaging [6], continuouswave terahertz digital holography based on thermal sensors [7][8][9][10][11][12][13][14][15] including Gabor in-line digital holography [7][8][9][10][11][12], phase retrieval for terahertz digital holography [9], biological specimen detection [10][11][12], and reconstruction research on terahertz off-axis digital holography [12][13][14][15].…”