Terahertz

Photonics Briefs

With Sunday comes my somewhat-weekly edition of Photonics Briefs. This week I'm going to feature a few papers from the latest Nature Photonics. Specifically: terahertz generation from silicon needles, innovations in solar panels, and a new technology for trapping atoms atomically.

First up, a group in Germany published a paper in Applied Physics Letters [Appl. Phys. Lett. 93, 091106 (2008)] demonstrating a new technique for generating the far-infrared terahertz radiation (to which this blog is named after). This new technique uses a "forest" of specially etched wires of pure-crystalline silicon. The wires are 300 nm across and 2 ?m tall. By shining a normal 780 nm laser pulse on the sample (which all terahertz labs will already have access to), THz radiation is emitted from the crystal due to some complex interactions with the electrons in the conduction band. I can't honestly say I understand how the process works, but this is definitely a novel approach.

Next up, a group has developed a double-sided solar cell. Traditionally, solar cells can only generate power with light illuminating one side of the cell, but with this technology a greater amount of light could be generated. This technology relies more on photosensitive dyes as opposed to traditional silicon, and could potentially drop the cost of solar cells significantly.

Why is two sides better? Imagine putting a mirror on the bottom of the solar panel, and instantly doubling its efficiency! [Bifacial dye-sensitized solar cells based on an ionic liquid electrolyte - p 693-698 Seigo Ito, Shaik M. Zakeeruddin, Pascal Comte, Paul Liska, Daibin Kuang & Michael Grätzel doi:10.1038/nphoton.2008.224]

Finally, a group has developed an optical trap - a laser that's used to capture atoms - using an airy function (which should appeal to the math nerds) as the shape of the beam. I can't comment on whether this is any more successful than other optical traps, but it is cool to know that atoms can be finely controlled by light. [Optical trapping: Riding along an Airy beam - pp652 - 653 Demetrios N. Christodoulides doi:10.1038/nphoton.2008.211]