N. J. J. van Hoof, S. E. T. ter Huurne, J. Gómez Rivas, and A. Halpin
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| Fig. 1 Schematic representation of the TR-THz-NF microscope. The addition of a Dove prism allows to perform spatially dependent time-resolved differential transmittance measurements. The red line denotes the pump beam that excites the sample, a beam splitter (BS) splits of a small portion of the power to probe THz transients using the near-field detector (orange line). The THz emitter is excited by the light blue line resembling a fiber carrying 1560nm light to generate a THz beam (dashed blue line) which is collected and focused onto the sample using lenses. |
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-24-32118
We demonstrate a novel method for measuring terahertz (THz) photoconductivity of semiconductors on length scales smaller than the diffraction limit at THz frequencies. This method is based on a near-field microscope that measures the transmission of a THz pulse through the semiconductor following photoexcitation by an ultrafast laser pulse. Combining back-excitation of the sample using a Dove prism, and a dual lock-in detection scheme, our microscope design offers a flexible platform for near-field time-resolved THz time-domain spectroscopy, using fluences available to typical laser oscillators. Experimental results on a thin film of gallium arsenide grown by metal organic chemical vapor deposition are presented as a proof-of-concept, demonstrating the ability to map the complex conductivity as well as sub-ps dynamics of photoexcited carriers with a resolution of λ/10 at 0.5 THz.
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