A water droplet
applied to a laser-processed silicon
upward, drawn by
an unusually strong
A laser surface treatment dramati- cally changes the wetting qualities
of silicon, with potential applications in
microfluidic lab-on-a-chip technologies
and electronic cooling.
The technique, developed by A.Y.
Vorobyev and Chunlei Guo at the University of Rochester, uses high-intensity femtosecond laser pulses to create tiny grooves
in the surface of silicon (Opt. Express
18, 6455). When liquid is introduced,
a supercapillary effect speeds its spread
along the grooves—even against gravity.
Fluid control is a challenge for microfluidic systems, since the capillary effect
applies to open surface grooves, and
usually it is stronger in tubes. However,
says Guo, “in our study, we turned our
surface grooves superhydrophilic,” so
they exhibit much stronger capillary
action than a closed tube with a typical
The researchers used a Ti:sapphire
laser system generating 65-fs pulses and a
100-µm-diameter laser spot to create tiny
grooves on the surface of a single-crystal
phosphorus-doped piece of silicon. They
scanned the sample across a beam to
produce a 22-mm-long microgroove.
Then they translated the sample 100 µm
to one side and started scanning another
groove, until they had a 22- 3 11-mm-
square sample. The microgrooves have
an average depth of about 40 µm. The
researchers saw fine microstructure and
nanostructure in the grooves.
Designing photovoltaic concentrators is a balancing act. The optic must concentrate a
lot of light, the intensity must be uniform, and the
design should have few elements. Pablo Benítez
and others from the Universidad Politécnica de
Madrid (Spain) and LPI (Altadena, Calif., U.S.A.)
recently reported a concentrator design comprised
of a Fresnel lens and a refractive secondary element that fulfills many of these requirements. Their
primary element is a multisectioned Fresnel lens
(left), and the secondary element (right) is molded
glass that includes a ring designed as a holder.
The article (Opt. Express 18(S1), A25) was
published in the inaugural issue of Energy Express, a special bi-monthly supplement
to Optics Express. The new journal will focus on the impact of light on sustainable
energy development and green technologies.
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8 | OPN Optics & Photonics News