Wiggler and undulator magnets

To scientists using vacuum ultraviolet and x rays the most important characteristics of an ideal radiation source would be a high intensity within a small solid angle and a high intensity within a small wavelength interval, both extending over a broad range of wavelengths. High spatial brightness (large flux within a small solid angle) permits the delivery of a large number of photons per second to a small sample. High spectral brightness (large flux within a narrow wavelength interval) is essential for high‐resolution spectroscopy. A high‐power tunable vuv and x‐ray laser would be ideal, but unfortunately such a laser does not yet exist. Conventional vuv sources (such as gas‐discharge lamps) and x‐ray sources (such as electron‐impact x‐ray tubes) can produce a large flux of radiation, most of which is indeed within a narrow bandwidth at particular fluorescent lines. However, the flux is diffused over a large solid angle and the wavelength is fixed. The continuum radiation from these sources is less intense than the narrow fluorescence peaks by about four orders of magnitude. Other sources exist, such as laser plasma sources and sliding‐spark devices, that provide more intense continuum radiation but have other limitations, such as low repetition rate, limited spectral range and attendant debris.