a b c d
In the Bern Advanced Glass Laser for Experiments at the University of Bern in Switzerland (a), a drive laser pulse (b) applied at the optimum angle
(c) produces EUV photons most efficiently and at wavelengths down to 8. 8 nm. The wavelength is set by the material from which the target is made (d),
limiting tunability – a limitation in all EUV laser schemes. Courtesy of Davide Bleiner, University of Bern.
that we would lose probing selectivity and
contrast,” Bleiner said.
Elliot R. Bernstein, a professor of chemistry at Colorado State, uses EUV lasers
because the photons pack a punch and ionize virtually any material. This allows researchers to unravel chemical reactions by
analyzing the initial compound, the intermediate products and the final result.
Bernstein and his group are interested
in the decomposition of energetic materi-
als, a substance class that includes rocket
fuel and explosives. Although rockets fly
and bombs burst, intelligently designing a
new version of what causes either can be
challenging because the precise details of
how energy is produced may be obscure.
“If you want the energy to be released
more slowly or more rapidly or in a different format, it’s very important to know
what’s actually happening, how the decomposition takes place,” Bernstein said.
He added that, although the current crop
of 46.9-nm EUV lasers work well for his
application, he would like to have systems
that fire faster to speed up experiments.
As for the future, EUV lasers are not
the only sources below 50 nm. Systems
based on high-order harmonics are being
developed at the University of Colorado
at Boulder, another core partner of the
National Science Foundation’s EUV
center, at Switzerland’s National Center
of Competence in Research Molecular
Ultrafast Science and Technology, and
elsewhere. For its part, the semiconductor
industry is investing heavily in incoherent
plasma sources. Compared with EUV
lasers, the first offers a shorter pulse
width, wavelength tunability and higher
repetition rates. The second can provide
magnitudes more power.
However, both alternatives also suffer
from disadvantages when compared with
EUV lasers. High-harmonic sources pro-
duce lower energy and spectrally broader
pulses. Plasma sources are limited in their