Abstract
In this Letter, optical-to-terahertz (THz) conversion of 800 nm femtosecond laser pulses in large-area bias-free InGaAs emitters based on photo-Dember (PD) and lateral photo-Dember (LPD) effects is experimentally investigated. We use metamorphic buffers to grow sub-micrometer thick ${{\rm In}_x}{{\rm Ga}_{1 - x}}{\rm As}$ layers with indium mole fractions $x = 0.37$, 0.53, and 0.70 on a GaAs substrate. A strong enhancement of THz output energy with an increase of indium content is observed. On the surface of the sample providing the strongest emission ($x = 0.7$), we have fabricated a $1.5\;{\rm cm}^2$ area of asymmetrically shaped metallic grating for LPD emission. This LPD emitter allows achieving high conversion efficiency of ${0.24} \cdot {{10}^{- 3}}$ and a broad generation bandwidth of up to 6 THz. We also demonstrate that there is no significant difference in the conversion efficiency when operating at 1 and 200 kHz repetition rates. Our results show that large-area LPD emitters give a convenient, competitive way to generate intense high-repetition-rate THz pulses.
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