High-gain harmonic generation free-electron laser at saturation

We report on observations of the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO/sub 2/ laser at a wavelength of 10.6 /spl mu/m was used to generate amplified FEL output at 5.3 /spl mu/m. Measurement of the frequency spectrum, pulse duration and correlation length of the 5.3-/spl mu/m output verified the longitudinal coherence of the light. At the exit of the device, measurements of the energy distribution of the electron beam indicated that the HGHG process had reached saturation. By comparing the intensities of the higher harmonics (2.65 /spl mu/m and 1.77 /spl mu/m) relative to the 5.3-/spl mu/m fundamental, additional evidence confirming saturated operation was obtained. These results agree with theoretical predictions at saturation. We also briefly describe the status of a new HGHG experiment at the Source Development Laboratory (BNL), aimed at achieving generation of 100-nm radiation.