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

Abstract

We report here on terahertz (THz) digital holography on a biological specimen. A continuouswave (CW) THz in-line holographic setup was built based on a 2.52 THz CO2 pumped THz laser and a pyroelectric array detector. We introduced novel statistical method of obtaining true intensity values for the pyroelectric array detector's pixels. Absorption and phase-shifting images of a dragonfly's hindwing were reconstructed simultaneously from single in-line hologram. Furthermore, we applied phase retrieval routines to eliminate twin image and enhanced the resolution of the reconstructions by hologram extrapolation beyond the detector area.

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

“…The terahertz images were captured by the pyroelectric detector (Pyrocam III, OphirSpiricon). The details of the experimental setup are available in reference [11].…”

“…The initial complex amplitude in the recording plane is U x y ( , ) d . (ii) The initial complex amplitude in the recording plane propagates back to the object plane by using the angular spectrum propagation integral, which is more suitable than the Fresnel approximation propagation for terahertz in-line digital holography [11]. So the complex amplitude in the object plane U ( , ) 0 ξ η ′ can be reconstructed by using the angular spectrum propagation integral…”

“…(iv) After applying the constraint conditions to the complex amplitude in the object plane, it is propagated back to the recorded plane, where the updated amplitude and phase distribution are obtained, and the new complex amplitude is considered as the initial value for the next iteration. The repeated propagating iterations result in suppression of the twin image in the final reconstructed image [9][10][11].…”

“…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].…”

Imaging outside the box: Resolution enhancement in X-ray coherent diffraction imaging by extrapolation of diffraction patterns

“…1,2 Such extrapolation has already been successfully demonstrated on light optical holograms and diffraction patterns, 1,2 terahertz in-line holograms, 3,4 and simulated diffraction patterns of crystalline samples. 5 The reported enhancement in resolution is at least twice the resolution obtained from non-extrapolated images.…”