A New Tunable Source for the FIR-THz Spectral Region
Abstract
The Grating Coupled Oscillator (GCO) has the potential to be a practical coherent source for far-infrared/terahertz (FIR/THz) research and applications. The GCO, simply an electron beam skimming a diffraction grating, has inherently many desirable features: continuously tunable from microwave to visible, continuous wave at room temperature, excellent spatial and spectral quality, stable, compact, robust, simple, and economical. Alternative sources (e.g. solid-state, short-pulse optical switches, free-electron lasers, and blackbody) do not share these characteristics. The GCO emits radiation by the Smith-Purcell effect: diffraction of the electron wake field. Spontaneous Smith-Purcell emission is easily generated. The difficulty lies in developing enough feedback in an open resonator (i.e. the grating) to produce sufficient coherent power without resorting to an enclosed resonator cavity, thereby limiting the tuning range. The aim of this project was to understand the beam-wave gain process though parametric studies in enough detail to pinpoint optimum resonator designs by which the GCO could operate well into the terahertz regime. Theoretical and experimental studies of the GCO indicate a three-wave interaction. Beating between the waves is observed in the sub-threshold radiant power with a cube root dependence on the current. Both gain and loss are greater than predicted. Observed parametric power dependence necessitated the development of a self-consistent field theory. The Grating Horn resonator magnified GCO intensity by 100 times. Many orders of magnitude further increase in power are predicted with the novel Lossless Resonator concept. GCO and Smith-Purcell experiments with moderate and high energy electron beams corroborate the underlying GCO theory. A list of related publications is included.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 26, 2003
- Accession Number
- ADA429258
Entities
People
- James H. Brownell
Organizations
- Dartmouth College