Near-Field Microscopy of Semiconductor and Metal Terahertz Resonators

Sub-wavelength local field enhancements are the most relevant characteristic of localized surface plasmons. These enhancements have triggered the interest for resonant metallic structures in sensing and spectroscopic applications. Local field enhancements have been thoroughly investigated at optical and infrared frequencies using near field probing techniques [1,2]. These techniques provide an excellent spatial resolution, but they are not sensitive to the individual field components. In this contribution, we demonstrate the near-field enhancement at THz frequencies in the proximity of silicon and gold resonant structures. These near fields are measured in a broadband THz time domain near-field microscope with micro-structured photo-conductive antennas that enable the individual measurement of the two in-plane field components. Our measurements clearly show the resonant response of the structures and the concomitant sub-wavelength field enhancement. THz microscopy also enables the determination of the phase of the near fields. Semiconductor resonant structures offer the possibility of ultrafast optical switching of localized plasmons (on a pico-second time scale) by optical pumping of charge carriers [3], which will enable the active control of sub-wavelength fields [4,5]. Since this excitation can be implemented in picosecond time scale, these structures can be used as a tool for ultrafast sub-wavelength THz microscopy [6].

References

[1] M. Schnell et al., Nature Photonics 3, 287 - 291 (2009)

[2] K. Wang et al., Appl. Phys. Lett. 85, 2715 (2004).

[3] G. Georgiou et al., Scientific Reports 4, 3584 (2014)

[4] V. Giannini et al., Opt. Express 18, 2797-2807 (2010).

[5] A. Berrier et al., Opt. Express 20, 5052-5060 (2012).

[6] M.Eisele et al., Nature Photonics 8, 841–845 (2014).

bhattacharya@amolf.nl