Spatial sampling of terahertz fields with sub-wavelength accuracy via probe-beam encoding

Abstract

Recently, computational sampling methods have been implemented to spatially characterize terahertz (THz) fields. Previous methods usually rely on either specialized THz devices such as THz spatial light modulators or complicated systems requiring assistance from photon-excited free carriers with high-speed synchronization among multiple optical beams. Here, by spatially encoding an 800-nm near-infrared (NIR) probe beam through the use of an optical SLM, we demonstrate a simple sampling approach that can probe THz fields with a single-pixel camera. This design does not require any dedicated THz devices, semiconductors or nanofilms to modulate THz fields. Using computational algorithms, we successfully measure 128 × 128 field distributions with a 62-μm transverse spatial resolution, which is 15 times smaller than the central wavelength of the THz signal (940 μm). Benefitting from the non-invasive nature of THz radiation and sub-wavelength resolution of our system, this simple approach can be used in applications such as biomedical sensing, inspection of flaws in industrial products, and so on.

Hyperspectral terahertz microscopy via nonlinear ghost imaging

“…2b). Interestingly, in our experiments, we were able to resolve features within the 50-100µm scale even in the presence of a relatively thick generation crystal (as opposed to the typical thickness requirements in other approaches [39][40][41][42]). The field-spatial spectra of each generating layer in the ZnTe do not mix incoherently (see Supplementary Section S2).…”

“…In terms of accessing new emerging wave domains, such as THz, the GI offer the option of closing relevant technological gaps while raising new challenges, such as the limited availability of THz Spatial Light Modulators (SLMs) and the coarse diffraction limit [26]. The combination of single-pixel imaging and TDS provides the exciting possibility to exploit novel space-time computational imaging approaches [31,32], and the TDS-GI has been recently proposed as viable for THz imaging [38][39][40][41][42]. The THz field can be densely sampled in space, giving access to sub-wavelength microscopy when an object is exposed to the near field of a THz source, detector, or mask.…”

Microwave Photonic Radars

“…Because of the line-by-line spectral manipulation capability of the SLMs, any linear signal processing function can be potentially executed. Typical examples include correlation [118], spatial Fourier transform [119], [120], matrix calculation [121] and mode shaping [122], [123].…”

Single-pixel terahertz imaging: a review

“…In Ref. 57 , a collimated probe beam was used to sample the collimated THz beam in a ZnTe crystal via electro-optic sampling (as shown in Fig. 5(a)).…”

“…(a) Experimental setup exploiting the patterning of the probe beam for THz imaging57 . The spatial shape of the pattern is encoded via an SLM on an optical beam, which is used to probe the collimated THz beam in the detection crystal.…”