Multi-pixel photoconductive emitters for the controllable generation of azimuthal and radial terahertz beams

Photoconductive emitters are useful for generating pulsed broadband THz generation. The emitters are multilayer devices that are made of metal electrodes deposited on the surface of semiconductor, as illustrated below. A fs laser pulse excites charge carriers in the biased semiconductor gaps creating varying photocurrents, which generate pulses at THz frequencies.

In this work, a 16-pixel interdigitated photoconductive emitter has been demonstrated to produce THz beams with electrically controlled polarisation states, including azimuthal, radial, and linear.

Changing the polarisation state has been achieved electrically by altering the bias voltage applied to individual pixels, which allowed bypass mechanical realignment.

To determine the optimal bias configuration for azimuthal and radial polarisation states, we conducted the dipole array modelling. To confirm that the generation of cylindrical-vector (azimuthal and radial) beams has been accomplished, the spatially-resolved electro-optic sampling has been used.

Both azimuthal and radial beams possess unique features, that make them applicable in fields of trapping and accelerating particles, as well as improved spatial resolution for imaging applications.

Recommended citation: Justas Deveikis and James Lloyd-Hughes, Opt. Express 30, 43293-43300 (2022).
Download Paper