Abstract-Measurement of Quadratic Terahertz Optical Nonlinearities Using Second-Harmonic Lock-in Detection

Shuai Lin, Shukai Yu, and Diyar Talbayev

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.10.044007

We present a method to measure quadratic terahertz optical nonlinearities in terahertz time-domain spectroscopy. We use a rotating linear polarizer (a polarizing chopper) to modulate the amplitude of the incident terahertz pulse train. We use phase-sensitive lock-in detection at the fundamental and the second harmonic of the modulation frequency to separate the materials’ responses that are linear and quadratic in a terahertz electric field. We demonstrate this method by measuring the quadratic terahertz Kerr effect in the presence of the much stronger linear electro-optic effect in the (110) $\mathrm{GaP}$ crystal. We propose that the method can be used to detect terahertz second-harmonic generation in noncentrosymmetric media in time-domain spectroscopy, with broad potential applications in nonlinear terahertz photonics and related technology.

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Abstract-Measurement of quadratic terahertz optical nonlinearities using second-harmonic lock-in detection

Shuai Lin, Shukai Yu, and Diyar Talbayev

https://journals.aps.org/prapplied/accepted/f107aAb0G65Ef81c305117d73c6c7f72816e559ca


We present a method to measure quadratic Terahertz optical nonlinearities in Terahertz time-domain spectroscopy. We use a rotating linear polarizer (a polarizing chopper) to modulate the amplitude of the incident THz pulse train. We use a phase-sensitive lock-in detection at the fundamental and the second harmonic of the modulation frequency to separate the materials' responses that are linear and quadratic in Terahertz electric field. We demonstrate this method by measuring the quadratic Terahertz Kerr effect in the presence of the much stronger linear electro-optic effect in the (110) GaP crystal. We propose that the method can be used to detect Terahertz second harmonic generation in noncentrosymmetric media in time-domain spectroscopy, with broad potential applications in nonlinear Terahertz photonics and related technology.

Abstract-A One‐Way Mirror: High‐Performance Terahertz Optical Isolator Based on Magnetoplasmonics

Shuai Lin,  Sinhara Silva,  Jiangfeng Zhou,  Diyar Talbayev



https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201800572

The magneto‐optical properties of conduction electrons in InSb in Voigt geometry at oblique incidence angles are explored. In parallel magnetic field, the oblique incidence reflectance exhibits high nonreciprocity, while the transmittance remains reciprocal. This phenomenology, combined with the unique magnetoplasmonic properties of InSb (high electron mobility, low effective mass, and temperature‐tunable bulk plasma frequency), allows the design of a simple and high‐performance THz optical isolator that works directly with linearly polarized light. It is demonstrated that the isolation power of the device exceeds 35 dB with the insertion loss of only −6.2 dB. The simplicity of the isolator design is unmatched among the proposed THz isolator concepts to date.

Abstract-Grating-coupled surface plasmons on InSb: a versatile platform for terahertz plasmonic sensing (Conference Presentation)

Diyar Talbayev, Shuai Lin

Tulane Univ. (United States)

Jiangfeng Zhou, Khagendra Bhattarai

Univ. of South Florida (United States)

Proc. SPIE 10210, Next-Generation Spectroscopic Technologies X, 102100X (June 9, 2017); doi:10.1117/12.2263717

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2632318

Detection and identification of molecular materials based on their THz frequency vibrational resonances remains an open technological challenge. The need for such technology is illustrated by its potential uses in explosives detection (e.g., RDX) or identification of large biomolecules based on their THz-frequency vibrational fingerprints. The prevailing approaches to THz sensing often rely on a form of waveguide spectroscopy, either utilizing geometric waveguides, such as metallic parallel plate, or plasmonic waveguides made of structured metallic surfaces with sub-wavelength corrugation. The sensitivity of waveguide-based sensing devices is derived from the long (1 cm or longer) propagation and interaction distance of the THz wave with the analyte. We have demonstrated that thin InSb layers with metallic gratings can support high quality factor “true” surface plasmon (SP) resonances that can be used for THz plasmonic sensing. We find two strong SP absorption resonances in normal-incidence transmission and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The sensitivity of this approach relies on the frequency shift of the SP resonance when the dielectric function changes in the immediate vicinity of the sensor, in the region of deeply sub-wavelength thickness. Our computational modeling indicates that the sensor sensitivity can exceed 0.25 THz per refractive index unit. One of the SP resonances also exhibits a splitting when tuned in resonance with a vibrational mode of an analyte, which could lead to new sensing modalities for the detection of THz vibrational features of the analyte.

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Abstract-Thin InSb layers with metallic gratings: a novel platform for spectrally-selective THz plasmonic sensing

Shuai Lin, Khagendra Bhattarai, Jiangfeng Zhou, and Diyar Talbayev
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-17-19448

We present a computational study of terahertz optical properties of a grating-coupled plasmonic structure based on micrometer-thin InSb layers. We find two strong absorption resonances that we interpret as standing surface plasmon modes and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The observed surface plasmon modes are well described by a simple theory of the air/InSb/air tri-layer. The plasmonic response of the grating/InSb structure is highly sensitive to the dielectric environment and the presence of an analyte (e.g., lactose) at the InSb interface, which is promising for terahertz plasmonic sensor applications. We determine the sensor sensitivity to be 7200 nm per refractive index unit (or 0.06 THz per refractive index unit). The lower surface plasmon mode also exhibits a splitting when tuned in resonance with the vibrational mode of lactose at 1.37 THz. We propose that such interaction between surface plasmon and vibrational modes can be used as the basis for a new sensing modality that allows the detection of terahertz vibrational fingerprints of an analyte.

© 2016 Optical Society of America

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