Gas-loaded free-electron laser experiments on the Stanford superconducting accelerator

The modification of the free-electron laser (FEL) on the Stanford superconducting accelerator to operate as a gas-loaded FEL (GFEL) is described. The addition of a gas to the wiggler chamber of a FEL changes the phase velocity of the electromagnetic wave, and so provides a simple method for wavelength tuning without changing beam energy or wiggler parameters. A wavelength shift of over 950 AA has been achieved from a vacuum wavelength of 1.6 mu m by using 15 torr of hydrogen gas, in agreement with the GFEL synchronism condition incorporating the index of refraction of the gas.<
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