K. Yamada et al., SATURATION OF CAVITY-MIRROR DEGRADATION IN THE UV FEL, Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment, 393(1-3), 1997, pp. 44-49
Behavior of surface and volume degradation in dielectric multilayer mi
rrors, manufactured with ion beam sputtering (IBS) and electron beam e
vaporation (EBE), was investigated in the ultraviolet (UV) wavelength
range. It was found in the IBS mirrors that the saturation in volume d
egradation enabled us to use the mirrors for a long period, because th
e surface degradation, causing only the narrowing of the mirror bandwi
dth, proved not to contribute seriously to the mirror loss as far as t
he mirrors are used at their optimized wavelength. This will reduce th
e cavity-mirror degradation problem in relatively high-gain free-elect
ron laser (FEL) system by carefully selecting the laser wavelength, al
though the wavelength tunability in FEL is limited to a certain extent
. In the EBE mirrors, only the surface-type degradation was found and
the evolution of the mirror degradation was different from that in IBS
mirrors. The detail on the mirror degradation in IBS and EBE mirrors
is shown in the text.