Ultra-fast laser looks to the stars

Scientists at the University of Konstanz in Germany and the National Institute of Standards and Technology (Nist) in the US have developed an ultra-fast laser that could be used to search for Earth-like planets orbiting distant stars.

The device offers a record combination of high speed, short pulses and high average power.

When combined with a frequency comb, an ultra-precise technique for measuring different colours of light, it is estimated that it can boost the sensitivity of astronomical tools searching for other Earth-like planets as much as 100 fold.

The laser emits 10 billion pulses per second, each lasting about 40 femtoseconds (quadrillionths of a second) with an average power of 650 milliwatts.

The device produces pulses 10 times more often than a standard Nist frequency comb while producing much shorter pulses than other lasers operating at comparable speeds.

It is also 100 to 1,000 times more powerful than typical high-speed lasers, producing clearer signals in experiments. The laser was built by Albrecht Bartels at the Center for Applied Photonics of the University of Konstanz.

"Astronomers look for slight variations in the colours of starlight over time as clues to the presence of a planet orbiting the star," the researchers explained.

"The variations are due to the small wobbles induced in the star's motion as the orbiting planet tugs it back and forth, producing minute shifts in the apparent colour of the starlight."

Currently, astronomers' instruments are calibrated with frequency standards that are limited in spectral coverage and stability.

Frequency combs could be more accurate calibration tools, helping to pinpoint even smaller variations in starlight caused by tiny Earth-like planets.

Such small planets would cause colour shifts equivalent to a star wobble of just a few centimetres per second. Current instruments can detect, at best, a wobble of about one metre per second.