Terahertz Digital Holographic Imaging of Voids Within Visibly Opaque Dielectrics

Abstract

Abstract-Terahertz digital off-axis holography (THzDH) has been demonstrated as a non-destructive tool for imaging voids within visually opaque dielectrics. Using a raster scanning heterodyne detector, the imager captures lensless transmission holograms formed by the interaction of a highly coherent, monochromatic beam with 3-D printed structures. Digital hologram reconstructions from two structures were used to measure the imager's modulation transfer function and to show that terahertz digital holography can provide sub-millimeter resolution images of voids within visually opaque printed structures. As a demonstration we imaged embedded air-and lossy dielectric filled-voids whose refractive indices differ from the host material.

Terahertz Spectroscopic Analysis in Protein Dynamics: Current Status

“…These systems have promoted the diffusion of THz radiation for spectroscopy applications. Thus, it was applied with success in various scientific fields e.g., gas sensing [75][76][77][78][79][80], chemical and pharmaceutical analysis [81,82], condensed matter [83][84][85], identification of crystalline polymorphs, microelectronics and security [86][87][88][89], agri-food industry [90] and cultural heritage [91], including the emerging support in the field of biomedicine and bio-imaging [92][93][94][95][96][97][98][99], etc. Thus, THz spectroscopy has become a valuable tool for rapid and non-invasive detection thanks to many advantages that make it particularly appealing for probing the intermolecular structure and dynamics of biomolecules [95,100,101].…”

THz coherent lensless imaging

“…The long wavelength implies that a fairly large numerical aperture (NA) should be employed to achieve an appropriate lateral resolution. For instance, in [100], when working at 0.495 THz (λ = 606 µm), for a sample located 16.3 cm away from the detector, a detection area of 20 × 20 cm is needed to achieve a lateral resolution comparable to the wavelength. To the authors' knowledge, most published works on lensless imaging at sub-THz band have been done using a raster-scanned single detector, due to the lack of large enough 2D arrays with adequate sensitivity [9].…”

Single-scan multiplane phase retrieval with a radiation of terahertz quantum cascade laser

“…In this field, THz imaging [1][2][3] represents one of the most promising approaches, since it provides spatially resolved information about the investigated objects. THz phase imaging (THz PI) [4,5], which includes pulse time-domain holography (PTDH) [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] as well as continuous wave (CW) holography [23][24][25][26][27][28][29][30], Hartmann wavefront sensing [31][32][33][34][35], shearorgaphy [36], ptychography [37][38][39][40][41], and other phase retrieval techniques [42][43][44][45][46][47][48][49], ...…”

“…And finally, success in solving practical problems of THz PI is guaranteed by the choice of a suitable combination of sources and detectors of radiation in this range of the electromagnetic spectrum. Early work on THz PI [4,[23][24][25]28] used single-pixel detectors in the raster scan mode of operation due to the lack of matrix detectors. As array detectors became available, a larger variety of THz PI works initiated such implementations [54][55][56][57][58].…”