Continuously tunable, high-power, single-mode radiation from a short-pulse free-electron laser

Area of Science:

• Physics
• Optics
• Laser Technology

Background:

• Free-electron lasers (FELs) offer tunable radiation but often lack narrowband coherence.
• Achieving high-power, narrowband output in the far-infrared spectrum is challenging.

Purpose of the Study:

• To demonstrate the first high-power, continuously tunable, narrowband radiation source in the far-infrared region using an FEL.
• To investigate methods for achieving spectral coherence and narrow linewidths in FEL output.

Main Methods:

• Utilized a Fox-Smith intracavity étalon to induce phase coherence among optical micropulses within the FEL cavity.
• Employed external Fabry-Pérot étalons for spectral filtering to isolate a single frequency line.
• Analyzed the influence of spontaneous emission and mode hopping on linewidth.

Main Results:

• Successfully generated phase-locked, discrete frequencies with 1 GHz spacing.
• Filtered a single line at 69 microm wavelength with 250 mW power.
• Achieved a spectral width as narrow as a single cavity mode (fraction of 25 MHz), limited by mode hopping.
• Demonstrated frequency scanning capabilities over a 1 GHz interval with unlimited potential.

Conclusions:

• The study presents a novel method for producing high-power, tunable, narrowband far-infrared radiation from an FEL.
• The developed technique significantly enhances spectral purity and control for far-infrared applications.
• This work opens new possibilities for frequency-agile sources in the far-infrared spectrum.