A HIGH-GAIN , TRANSFORM-LIMITED FAR-INFRARED FREE-ELECTRON LASER AMPLIFIER SEEDED BY A THZ SINGLE-FREQUENCY DIFFERENCE FREQUENCY GENERATOR

Narrow-line coherent radiations are important for applications requiring high spectral resolution. A freeelectron-laser oscillator is usually complicated in alignment and hard to produce transform-limited linewidth without an intracavity dispersive optical element. An SASE free-electron laser, however, produces broad-band laser-like output in a single electron transit. In this paper, we discuss a high-gain, narrow-line farinfrared free-electron laser amplifier seeded by a THz single-frequency difference frequency generator. The wavelength-tunable THz seed laser is realized by using nonlinear frequency mixing in Nd:YAG-laser-pumped periodically-poled lithium niobate. The high-gain freeelectron laser amplifier employs a 2-5 MeV microwave gun and a single-pass solenoid-derived stagger wiggler for producing transform-limited wavelength-tunable THz radiations between 100-300 micron wavelengths.