| Free electron lasers (FELs) produce an intense beam of coherent radiation by passing energetic electrons through a periodic magnetic field. Since the properties of the resulting laser beam are directly determined by the electron beam and magnetic field, FELs can provide remarkable flexibility in wavelength, pulse width, and power. With megawatt peak powers, picosecond pulse durations, and continuously tunable wavelength throughout the infrared, FELs can be useful instruments for basic scientific research. This work discusses the design, operation, and first experiments with FIREFLY, an FEL built at Stanford University to operate in the far-infrared between 10 and 100 microns. We discuss general FEL design principles and evaluate the performance of the FIREFLY undulator and optical resonator. We present measurements of enhanced spontaneous emission from FIREFLY together with direct observation of electron bunch structure. We examine FIREFLY laser operation under a range of conditions, including third harmonic and optical klystron operation. We analyze wavelength switching between adjacent peaks in an optical klystron gain spectrum, first seen with FIREFLY. Finally, we discuss several experiments made possible by the existence of this extremely bright, short duration far-infrared source, and examine some results concerning two-photon absorption in indium arsenide obtained with the mid-infrared FEL at Stanford. |
