Lasers enable ultra-sensitive detection of radio waves

March 06, 2014 // By Jean-Pierre Joosting
When detecting radio waves, 'noise' in the detector of the measuring instrument limits how sensitive and precise the measurements can be. Researchers at the Niels Bohr Institute have developed a method where they can avoid noise by means of laser light and can consequently achieve extreme precision of measurements.

'Noise' in the detector of a measuring instrument is first and foremost due to heat, that causes atoms and electrons to move chaotically, so the measurements become imprecise. The usual method to reduce noise in the detector of the measuring equipment is therefore to cool it down to 5-10 degrees Kelvin, which corresponds to around -265 °C. This is expensive and still does not enable the weakest signals to be measured.

"We have developed a detector that does not need to be cooled down, but which can operate at room temperature and yet hardly has any thermal noise. The only noise that fundamentally remains is so-called quantum noise, which is the minimal fluctuations of the laser light itself," explains Eugene Polzik, Professor and Head of the research center Quantop at the Niels Bohr Institute at the University of Copenhagen.

The method, called optomechanics, is a complex interaction between a mechanical movement and optical radiation.

The nanomembrane itself is made of silicon nitrate and is coated with a thin layer of aluminum, since there has to be a metallic substance to better interact with the electric field. The membrane is separated from the surroundings by being enclosed in a vacuum chamber so that it responds as if it had been cooled down to two degrees Kelvin (-271 °C). Source: Ola Jakup Joensen, NBI.