Improvement of terahertz imaging with a dynamic subtraction technique

Jiang, Zhiping; Xu, Xiaobin; Zhang, X.-C.

doi:10.1364/ao.39.002982

Cited by 137 publications

(59 citation statements)

References 12 publications

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“…Terahertz imaging systems based on electro-optical sampling and a conventional CCD camera are reported to be able to achieve real time imaging [5][6]. However these systems require high power laser sources in order to obtain a sufficient signal to noise ratio (SNR).…”

Section: Terahertz Single Pixel Imaging Based On a Nipkow Diskmentioning

confidence: 99%

Terahertz single pixel imaging based on a Nipkow disk

Grant

Saha

et al. 2012

Opt. Lett.

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Section: Terahertz Single Pixel Imaging Based On a Nipkow Diskmentioning

confidence: 99%

Terahertz single pixel imaging based on a Nipkow disk

Grant

Saha

et al. 2012

Opt. Lett.

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“…The two-dimensional electro-optic sampling with a high-frame rate CCD or CMOS camera (2), (12) is promising as the detection scheme if a bright THz emitter is available. All of these improvements contribute to a faster THz image acquisition.…”

Section: Resultsmentioning

confidence: 99%

Applications of Terahertz Time-Domain Reflectometry

et al. 2007

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A reflection-type terahertz (THz) time-domain spectroscopy (TDS) is applied for non-contact and non-destructive diagnosis of the surface and inner-structure of test samples. Generally, a reflection-type spectrometer, or imager, is preferable compared to that of a transmission-type one for observing the inner-structure of samples. Reflection of the THz pulse from samples was observed by using the reflection-type THz-TDS system at room temperature and in dry atmosphere. The THz radiation beam with normal incidence was focused on to the sample at a normal incidence by using an off-axis parabolic mirror. The emitter and detector were photoconductive dipole antennas. Femtosecond laser was used for generating pump and probe pulses for excitation and gating the photoconductive antennas. The center wave length of the laser was 800 nm and the repetition rate was 80 MHz. The emitter bias voltage had a 10-kHz sinusoidal wave form with a 100-V amplitude. The reflected THz electromagnetic wave was focused on the detector antenna by using an off-axis parabolic mirror and a hemispherical substrate lens made of high resistivity silicon with a diameter of 13-mm. The timing of the probe pulse was varied against the pump pulse to obtain time-domain wave forms of the THz radiation. The spectrum was obtained by Fourier transformation of the observed wave form. The raster scan imaging was performed by moving the sample stage in the directions perpendicular to the propagation direction of the THz electromagnetic wave. At each position of the raster scanning, the reflection THz wave form was measured. The reflection images of three samples, that is, a bank bill, a high-voltage cable, and an indented impression on a paper, are observed. The watermark of the bank bill, the indented impression, and a flaw in the cable are detected successSfully. The cable structure, THz wave incidence direction and scanned direction are shown in Fig.1. The observed THz optical coherence tomography (THz-OCT) depth profile of an old high voltage cable is shown in Fig.2. The sheath surface, cloth layer and shield surface were clearly identified in this depth profile. In addition, a defect is identified in the cloth layer simultaneously. From this result, THz-OCT is expected to be useful for checking the aged high-voltage cables without stopping the operation of the high voltage cables. These results indicate that THz-imaging based on THz-TDS is potentially useful for the analysis of surfaces and inner-structures of products made with various materials. MemberA reflection-type terahertz (THz) time-domain spectroscopy (TDS) is applied to non-contact and non-destructive diagnosis of the surface and inner-structure of test samples. Raster scan imaging and THz optical coherence tomography (THz-OCT) are demonstrated for a bank bill, a high voltage cable and an indented impression on a memo-pad paper. The watermark of the bank bill, the indented impression, and a flaw in the cable are detected successfully. These results indicate that THz imaging is potentially u...

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“…The terahertz information was extracted using both the balanced electro-optic detection [32] and dynamic subtraction techniques. [33] The terahertz time-domain signal was recorded by varying the optical path difference between the terahertz beam and the probe beam. One hundred temporal images were captured at each time delay and the time window was 17 ps.…”

Section: Methodsmentioning

confidence: 99%

Generation of Radial Polarized Lorentz Beam with Single Layer Metasurface

Guo

Wang

et al. 2017

Advanced Optical Materials

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as well as ultrafast phenomena sensing. [11] Practical applications for nondiffracted waves include light collimating, focusing, and shaping. [12][13][14] The Lorentz beam is a nondiffracted wave that is characterized by small size, long focal length, and extended transmission distance. [12] Typical techniques to produce Lorentz beams usually involve combinations of multiple optical elements. However, such systems are bulky, complicated, and inconvenient. To generate such novel beams simply, we employ a single layer metasurface device to modulate simultaneously the amplitude and polarization of the illuminating light. Metasurfaces are viewed as a kind of artificial material composed of periodic subwavelength metal or dielectric structures. When coupled resonantly to the electric and/or magnetic components of an incident electromagnetic field, they provide a spatially varying optical response (e.g., scattering amplitude, phase, and polarization). With the advantage of easy-etching, ultrathin as well as miniaturization, a broad range of applications of metasurfaces has been reported, including superlenses, [15,16] wave plates, [17][18][19] nonlinear optics, [20] and holograms. [21] However, these previous studies were focused on modulating one attribute of light beams, for example amplitude, phase or polarization. Several studies were reported to have modulated the phase [22] and polarization direction. [23] Only numerical simulations are carried out to demonstrate the ability of metasurface for multiple parameters modulation because double-layer structures [24] are difficult to fabricate. Traditionally, the concentric metal-ring wire grid is used to achieve radial polarization. [25][26][27] The structure is relatively simple but fails to generate amplitude modulation. Furthermore, circularly polarized light is required to generate radially polarized light; nevertheless, it comes accompanied by an unexpected vortex phase distribution. In this work, a designed metasurface is fabricated consisting of crosses of various sizes and orientations. The variation in size is employed to modulate the amplitude whereas variation in orientation is used to modulate the polarization distribution. With right/left circularly polarized (RCP/LCP) incidence, the output polarization may be radial or angular, whereas the amplitude obeys the Lorentz distribution. Nine cross structures were fabricated to achieve certain desired amplitude and polarization modulations. The polarization and amplitude distributions of the beam generated by the device are detected using a terahertz focal plane imaging system. A strong agreement between theoretical and experimental results was

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Improvement of terahertz imaging with a dynamic subtraction technique

Cited by 137 publications

References 12 publications

Terahertz single pixel imaging based on a Nipkow disk

Terahertz single pixel imaging based on a Nipkow disk

Applications of Terahertz Time-Domain Reflectometry

Generation of Radial Polarized Lorentz Beam with Single Layer Metasurface

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