Abstract-Time-resolved terahertz time-domain near-field microscopy

                                                             

                                                                  

N. J. J. van Hoof, S. E. T. ter Huurne, J. Gómez Rivas, and A. Halpin

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.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Resonant terahertz probes for near-field scattering microscopy

Thomas Siday, Michele Natrella, Jiang Wu, Huiyun Liu, and Oleg Mitrofanov

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-22-27874


We propose and characterize a scattering probe for terahertz (THz) near-field microscopy, fabricated from indium, where the scattering efficiency is enhanced by the dipolar resonance supported by the indium probe. The scattering properties of the probe were evaluated experimentally using THz time-domain spectroscopy (TDS), and numerically using the finite-difference time-domain (FDTD) method in order to identify resonant enhancement. Numerical measurements show that the indium probes exhibit enhanced scattering across the THz frequency range due to dipolar resonance, with a fractional bandwidth of 0.65 at 1.24 THz. We experimentally observe the resonant enhancement of the scattered field with a peak at 0.3 THz. To enable practical THz microscopy applications of these resonant probes, we also demonstrate a simple excitation scheme utilizing a THz source with radial polarization, which excites a radial mode along the length of the tip. Strong field confinement at the apex of the tip, as required for THz near-field microscopy, was observed experimentally.

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