We report on an experimental investigation characterizing the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO2 laser at a wavelength of 10.6 microm was used to generate amplified FEL output at 5.3 microm. Measurement of the frequency spectrum, pulse duration, and correlation length of the 5.3 microm output verified that the light is longitudinally coherent. Investigation of the electron energy distribution and output harmonic energies provides evidence for saturated HGHG FEL operation.

We report on the experimental investigation of high-gain harmonic generation carried out at the Accelerator Test Facility at Brookhaven National Laboratory. A seed CO2 laser at a wavelength of 10.6μm was used to generate FEL output at a 5.3-μm wavelength. The duration of the output pulse was measured using a second-harmonic intensity autocorrelator, and the coherence length was measured using an interferometer. We also measured the energy distribution of the electron beam after it exited the second undulator, observing behavior consistent with that is expected at saturation. The intensity of the harmonic components of the output at 2.65 and 1.77μm was determined relative to that of the 5.3-μm fundamental. Finally, using a corrector magnet upstream of the radiator, steering effects on the trajectories of the electron and light beams were studied.

We report on the first lasing of a high-gain harmonic generation (HGHG) free-electron laser (FEL). The experiment was conducted at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). This is a BNL experiment in collaboration with the Advanced Photon Source (APS) at Argonne National Laboratory. A preliminary measurement gives a high-gain harmonic generation (HGHG) pulse energy that is 2×107 times larger than the spontaneous radiation. In a purely self-amplified spontaneous emission (SASE) mode of operation, the signal was measured as 10 times larger than the spontaneous radiation in the same distance (∼2 m) through the same wiggler. This means the HGHG signal is 2×106 times larger than the SASE signal. To obtain the same saturated output power by the SASE process, the radiator would have to be 3 times longer (6 m).

A high-gain harmonic-generation free-electron laser is demonstrated. Our approach uses a laser-seeded free-electron laser to produce amplified, longitudinally coherent, Fourier transform-limited output at a harmonic of the seed laser. A seed carbon dioxide laser at a wavelength of 10.6 micrometers produced saturated, amplified free-electron laser output at the second-harmonic wavelength, 5.3 micrometers. The experiment verifies the theoretical foundation for the technique and prepares the way for the application of this technique in the vacuum ultraviolet region of the spectrum, with the ultimate goal of extending the approach to provide an intense, highly coherent source of hard x-rays.

The low-energy undulator test line (LEUTL) is being built and will be tested with a short beam pulse from an rf gun in the Advanced Photon Source (APS) at the Argonne National Laboratory. In the LEUTL a beam chopper is used after the rf gun to deflect the unwanted beam to a beam dump. The beam chopper consists of a permanent magnet and an electric deflector that can compensate for the magnetic deflection. A 30-kV pulsed power supply is used for the electric deflector. The chopper subsystem was assembled and tested for beamline installation. The electrical and beam properties of the chopper assembly are presented.

All major magnets of the Advanced Photon Source (APS) have now been measured and installed in the facility. This paper describes the mechanical design, construction, procurement philosophy and methodology, and lessons learned from the construction and procurement of more than 1500 magnets for the APS storage ring, injector synchrotron ring, and positron accumulator ring