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Nonlinear Optics in Gas Phase by Terahertz and Optical Pulses


  Amit Beer  ,  Dror Hershkovitz  ,  Sharly Fleischer  
 Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University 6997801, Israel
Tel-Aviv University center for Light-Matter-Interaction, Tel Aviv 6997801, Israel

Terahertz field induced second harmonic generation (TFISH) is an all-optical technique for detection of broad-band THz fields [1], [2].
The technique relies on the nonlinear mixing of three input fields – a THz field (ETHz) and two optical fields (Eω, Eω) via the 3rd order susceptibility, Χ(3), to yield a signal field with frequency ωTFISH≈2ω.
In this work we explore the severe effects of phase-mismatch in TFISH at dilute gas and demonstrate a dramatic increase of few-tens-fold in the signal obtained in atmospheric air by placing an iris at the interaction volume of the interacting fields.
The iris-assisted TFISH provides a uniquely elegant platform for studying nonlinear phase-matching  [3], [4] and is further utilized for characterizing the elusive length of interaction, L.
The effects of self-phase modulation and dilute plasma formation are shown to significantly contribute to the overall phase-matching conditions and also manifest by enhanced TFISH efficiency [5].

In addition to providing a test-bed and a simulator for semi-infinite gas cells with full control over the relevant experimental parameters such as Δk (by changing the gas type and/or density), beam geometries, interaction length (by varying the iris position), TFISH provides new means to exploring the rotational dynamics of gas phase molecules under the action of, and long after their interaction with the THz field. I will also present our preliminary results on this front.

 

[1]          D. J. Cook, J. X. Chen, E. A. Morlino, and R. M. Hochstrasser, “Terahertz-field-induced second-harmonic generation measurements of liquid dynamics”, Chem. Phys. Lett., vol. 309, pp. 221–228, 1999.

[2]          J. Chen, P. Han, and X. C. Zhang, “Terahertz-field-induced second-harmonic generation in a beta barium borate crystal and its application in terahertz detection”, Appl. Phys. Lett., vol. 95, no. 1, pp. 2007–2010, 2009.

[3]          X. Lu, N. Karpowicz, and X.-C. Zhang, “Broadband terahertz detection with selected gases”, J. Opt. Soc. Am. B, vol. 26, no. 9, p. A66, Sep. 2009.

[4]          N. Karpowicz, X. Lu, and X. C. Zhang, “Terahertz gas photonics", J. Mod. Opt., vol. 56, no. 10, pp. 1137–1150, Jun. 2009.

[5]          A. Beer, D. Hershkovitz, and S. Fleicher, “Iris-assisted terahertz field-induced second-harmonic generation in air”, vol. 44, no. 21, pp. 5190–5193, 2019.