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(a) Optical setup to achieve angle self-tuning vertical illumination of the TW-photomixers, with added probe-beam path. The mode filter is not necessary using an interdigitated CPS (Ref. 5) or fiber illumination. (b) Pump and probe beams on the photomixer stripline. (c) Layer geometry of the thin and thick samples. The BR in the thin samples was erroneously fabricated using GaAs/AlAs instead of InGaAs/AlAs layers, so that NIR-absorption was also taking place there and a high reflectivity at 780 nm was not given. This was unfortunate with respect to obtaining good mixers, but gave rise to investigate the here proposed effect.
(a) Measured THz-power with and without probe beam when stepping the photomixer block through the probe and pump beams, which are fixed in space, along the stripline (thin sample). (b) Photocurrents and THz reabsorption coefficient A. The two colors of the probe beam appear split by the grating G2.
Measured THz-losses due to NIR-illumination with a probe beam as a function of THz-frequency for the samples with thick and thin LT-GaAs-layer, normalized by the estimated NIR probe power in the CPS gap. Good and bad THz efficiency refer to growth temperatures of 250 °C and 325 °C, respectively.
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