Enhancing source efficiencies, tunable metasurfaces and subwavelength detectors at Terahertz frequencies

Terahertz (THz) frequencies form a very interesting part of the electromagnetic spectrum: the gap between infrared and the microwave bands, typically with free space wavelengths in the range of several 10s of microns to few millimeters. Corresponding photon energies range from less than 1 to several 10s of meV. As a result of this, not only are these frequencies completely non-ionizing, most molecules have spectral fingerprint in this range emanating from vibrational and rotational modes in them. This makes the THz band extremely relevant for non-invasive, non-contact spectroscopic purposes. Furthermore, due to relatively slow oscillations of the electric fields, using relatively simple opto-mechanics, the field transient can be measured, which opens a plethora of information for the systems under studies. However, the research in this field has not yet reached a mature stage mainly due to the unavailability of efficient emitters in this frequency range. In this talk, I’ll present our work on THz photo-conductive antenna-based sources and how to enhance their efficiencies through nano- and micro-patterning [1,2]. Furthermore, I’ll discuss a novel technique to design mechanically tunable metasurface band-pass filter at THz frequencies [3]. In the end, I’ll discuss a technique to measure the subwavelength local transient electric fields in the vicinity of micro-structures with our in-house THz micro-spectroscopy setup which we have developed in TIFR during my tenure and an in-house near-field subwavelength detector which we are working on presently.

[1] APL Photonics 3, 051706 (2018)
[2] IEEE Transactions on Terahertz Science and Technology, 9, 2, 193-199 (2019)
[3] Opt. Mater. Express 8, 3382-3391 (2018)