What are the light sources in VUV?

The synchrotron radiation facilities provide intense continuum radiation from the microwave (harmonics of the driving RF field) to X-Ray spectral regions, emitted by high-energy electrons that are centripetally accelerated in the magnetic fields of a storage ring. Their beams are polarized and quasi-collimated.

This is the ideal, the most powerful and certainly the most expensive light sources ever built, with their enormous sizes (several hundred meters of diameter) and their complexities in an Ultra High Vacuum environment.

There are less than one hundred synchrotron facilities around the world.

A FEL is the fourth generation of synchrotron. It is a kind of laser using electrons accelerated up to the speed of light and then crossing a very long undulator (linear array made with magnets). Due to the alternation of polarities of the magnets, the electron path becomes sinusoidal. This effect produces an emission of radiation. FELs have a lot of common points with the synchrotrons: their emissions regions, their powers, their sizes, their complexities and their costs. Such lasers are tunable from microwave to X-Ray.

When the output of a high-power pulsed laser is focused onto a solid target, a short-lived (nanosecond), high-temperature (50~100 eV), high-density (~1021 cm-3) plasma is created. The radiation from certain target materials, particularly the rare earths and neighboring metals on the periodic table, produces a strong VUV quasi-continuum that is essentially free of discrete lines. The continua are most intense in the 4 to 30 nm region, but often extend to about 180 nm.

Because of their limited emission range, LPP are mainly used in astronomy and semiconductor industries (microlithography). Arcs, sparks and discharges.

Several VUV light sources emit VUV lines and/or continuum radiations. They are based on gas discharges, high-pressure arcs, low-pressure and vacuum sparks. These sources are not as intense as synchrotron radiation and laser-induced plasmas, but they are portable and inexpensive.

• H₂ and D₂ Discharges: 115~350 nm, bulb material dependent;
• Ar mini-Arc: from near UV to approximately 115 nm;
• Inert Gas Discharges: Plasma discharges generated through He, Ar, Kr, and Xe cover mainly the 20 to 700 nm region. Some available designs are Penning, pumped hollow cathode, Capillary Plasma or Damany source.