Dark Pulse Laser emits trillionths-of-a-second bursts of nothing

19:31 June 12, 2010

Colorized trace of pulses from the NIST/JILA dark pulse laser, indicating the light output nearly shuts down about every 2.5 nanoseconds (Image: NIST)

OK, you’re right, it 's impossible to actually beam “nothing” across a room. It is, however, possible to beam light across a room, sending information in the form of extremely short dips in that light. That’s what America’s National Institute of Standards and Technology (NIST) has been doing with its dark pulse laser. Whereas regular lasers transmit information by using darkness as a zero point and light pulses as data, this one uses light as a zero point, with darkness as the data.

The first question, of course, is “Why?”. For starters, the dark pulses are stunningly short - just 90 picoseconds (trillionths of a second), which could be useful for measuring very short timescales. Also, unlike light pulses, they are not subject to distortion. This could make them well-suited to signal processing.

So, why can’t the researchers just use a regular laser, and simply get it to pulse off instead of on? It’s all about the qdots. The dark pulse laser contains millions of 10-nanometer-wide quantum dots, which are made from semiconductor materials produced at NIST. When an electrical current is sent into the laser, the qdots all emit infrared light, which is then amplified by the current. Due the unusual energy-recovery dynamics of the qdots, they are able to stabilize dark pulses in a way not possible with other light sources.

NIST collaborated on the project with the Joint Institute for Laboratory Astrophysics (JILA) from the University of Colorado, Boulder. The team is now considering the use of semiconductor lasers, of which the dark pulse is one, in advanced applications such as atomic clocks.