Abstract-Stokes–Mueller method for comprehensive characterization of coherent terahertz waves

                                                                   
Xin Chai, Xavier Ropagnol, Luis. Sanchez Mora, S. Mohsen Raeiszadeh, Saffiedin Safavi-Naeini, François Blanchard, Tsuneyuki Ozaki

• • https://www.nature.com/articles/s41598-020-72049-9

Ideally, the full characterization of coherent terahertz (THz) pulses would provide information on the amplitude and direction of its THz electric field, in space and in time, with unlimited dynamic range. Here, we propose and demonstrate a new approach based on the Stokes–Mueller formalism. Our approach can measure the full temporal and spatial variation of coherent THz fields, as well as its polarization state with a high dynamic range. This method employs a simple configuration, using a polarization state analyzer after the electro-optic sampling crystal. This technique could allow high sensitivity due to its ability to use thick detection crystals, which also would lead to improved spectral resolution by allowing longer scans in the time domain.

Abstract-Terahertz microscopy assisted by semiconductor nonlinearities

François Blanchard, Xin Chai, Tomoko Tanaka, Takashi Arikawa, Tsuneyuki Ozaki, Roberto Morandotti, and Koichiro Tanaka

Fig. 1. Experimental setup. (a) THz transmission scheme using wire-grid polarizer and a LN sensor. (b) Illustration of the sample used for near-field investigations. (c) Visible image of a gold ring array structure patterned on a In0.53Ga0.47As${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ epilayer thin film.

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-20-4997#articleFigures

Terahertz (THz) imaging is currently based on linear effects, but there is great interest on how nonlinear effects induced by terahertz radiation could be exploited to provide extra information that is unobtainable by conventional imaging schemes. In particular, at field strengths on the order of 100  kV cm−1$100\mathrm{kV}{\mathrm{cm}}^{-1}$ to 1  MV cm−1$1\mathrm{MV}{\mathrm{cm}}^{-1}$, transmission properties inside semiconductor materials are largely affected at the picosecond time-scale, which raise the prospect of interesting nonlinear imaging applications at THz frequencies. Here, we experimentally investigate a method to map the two-dimensional nonlinear near-field distribution of an intense THz pulse passing through a thin film-doped semiconductor. By inserting a metamaterial structure between the electro-optic sensor and the doped film, the nonlinear near-field dynamics shows a different and enhanced contrast of the sample when compared to its linear counterpart.

© 2018 Optical Society of America

Abstract-Subcycle Terahertz Nonlinear Optics

Xin Chai, Xavier Ropagnol, S. Mohsen Raeis-Zadeh, Matthew Reid, Safieddin Safavi-Naeini, and Tsuneyuki Ozaki

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.143901

The nonlinear interaction of subcycle electromagnetic radiation with matter is the current frontier in ultrafast nonlinear optics and high-field physics. Here, we investigate nonlinear optical effects induced by intense, subcycle terahertz radiation in a doped semiconductor. We observe a truncation of the half-cycle terahertz pulse and an emission of high-frequency terahertz photons. We attribute our observations to the abrupt current drop caused by strong intervalley scattering effects. By adding an extra half-cycle terahertz pulse with opposite polarity, we monitor the evolution of the nonlinear carrier dynamics during a quasi-single-cycle pulse. Our results demonstrate the differences between nonlinear effects for subcycle and multicycle terahertz pulses. It also suggests a new approach to subcycle control of terahertz waveforms, and the generation of high-order terahertz harmonics could be realized by using multicycle pulses.

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Abstract-Intense terahertz field effects on photoexcited carrier dynamics in gated graphene

Hassan A. Hafez¹, Pierre L. Lévesque², Ibraheem Al-Naib^3,4, Marc M. Dignam³, Xin Chai¹, Saman Choubak⁵, Patrick Desjardins⁵, Richard Martel² and Tsuneyuki Ozaki^1,a)


a) Author to whom correspondence should be addressed. Electronic mail: ozaki@emt.inrs.ca
Appl. Phys. Lett. 107, 251903 (2015); http://dx.doi.org/10.1063/1.4938081

We study nonlinear effects of intense terahertz (THz) field on photoexcited carrier dynamics in gated monolayer graphene. By employing optical-pump/intense-THz-probe spectroscopy on lightly doped graphene, we observe a crossover from negative to positive photo-induced THz differential transmission as the THz probe field is increased. We attribute this qualitative change in the response to a crossover from a regime where the photo-induced increase in the carrier density dominates the differential response to one where a THz-field-induced increase in the scattering rate dominates.