Numerical modeling of a table-top tunable Smith-Purcell Terahertz free-electron laser operating in the super-radiant regime

Terahertz (THz) radiation occupies a very large portion of the electromagnetic spectrum and has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiation such as x-rays. One path for generating copious amount of tunable narrow-band THz radiation is based on the Smith-Purcell free-electron laser (SPFEL) effect. In this Letter we propose a simple concept for a compact two-stage tunable SPFEL operating in the superradiant regime capable of radiating at the grating's fundamental bunching frequency. We demonstrate its capabilities and performances via computer simulation using the conformal finite-difference time-domain electromagnetic solver {\sc vorpal}.