Abstract-Multicycle terahertz pulse generation by optical rectification in LiNbO3, LiTaO3, and BBO crystals

Dogeun Jang and Ki-Yong Kim

 (a) Experimental setup for multicycle THz generation and detection. (b) Input laser spectrum measured (black line) before entering the experimental setup with a Gaussian fit (red line). (c) Measured (black dotted line) and estimated (red solid line) laser pulse duration as a function of input GDD (top 𝑥$x$-axis), practically controlled by varying the distance (bottom 𝑥$x$-axis) between the grating pair in the laser compressor. (d) Focused THz beam profile captured by a microbolometer focal plane array.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-14-21220

We report multicycle, narrowband, terahertz radiation at 14.8 THz produced by phase-matched optical rectification of femtosecond laser pulses in bulk lithium niobate (LiNbO3) crystals. Our experiment and simulation show that the output terahertz energy greatly enhances when the input laser pulse is highly chirped, contrary to a common optical rectification process. We find this abnormal behavior is attributed to a linear electro-optic (EO) effect, in which the laser pulse propagating in LiNbO3 is modulated by the terahertz field it produces, and this in turn drives optical rectification more effectively to produce the terahertz field. This resonant cascading effect can greatly increase terahertz conversion efficiencies when the input laser pulse is properly pre-chirped with additional third order dispersion. We also observe similar multicycle terahertz emission from lithium tantalate (LiTaO3) at 14 THz and barium borate (BBO) at 7 THz, 10.6 THz, and 14.6 THz, all produced by narrowband phase-matched optical rectification.

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