Fig. 1: Concept and experimental setup of THz generation from quantum well emitters. | Light: Science & Applications

Fig. 1: Concept and experimental setup of THz generation from quantum well emitters.

From: Scalable high-repetition-rate sub-half-cycle terahertz pulses from spatially indirect interband transitions

Fig. 1

a When an intense NIR femtosecond light pulse (red arrow) generates electron–hole pairs in the highest hole subband and the lowest electron subband (black) of a type-II aligned QW, an ultrafast dipole moment arises owing to direct excitation of spatially separated electron–hole pairs. Inset: a mostly symmetric, sine-shaped THz waveform is expected. b The QWE consisting of 100 GaAs0.87Sb0.13/In0.141Ga0.859As QWs separated by In0.124Al0.876As barriers is pumped in reflection geometry under an angle of incidence of 65°. c Spectral intensity of the fundamental (dark red dotted line) and compressed (red solid line) laser pulses. d Femtosecond pulses of an ytterbium fibre laser are spectrally broadened and compressed to 30–90 fs using self-phase modulation in a fused silica medium (χ(3)) in a multi-pass cell (MPC). The pulses act both as a pump for the quantum well emitters and as a gate in the electro-optic detection using a GaSe crystal with a thickness of 6 µm as electro-optic crystal (EOX). BS beam splitter, τEOS delay time, OAP off-axis parabolic mirror, ITO fused silica window with one-sided indium tin oxide coating, Ge 500-µm-thick germanium window, λ/4 quarter-wave plate, WP Wollaston prism, PDs balanced photodiodes

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