Optical-electrical-mechanical laser setup sensitively detects radio waves at room temperature
| PhD students Tolga Bagci and Anders Simonsen oversee the radio-wave-sensing hardware. (Image: Niels Bohr Institute) |
Researchers at the Niels Bohr Institute (Copenhagen, Denmark), DTU Nanotech (Lyngby, Denmark), and the Joint Quantum Institute/NIST (College Park, Maryland) have developed an ultralow-noise room-temperature approach to radio-wave detection, using a 1 mW laser beam to read the mechanical vibrations of an electrical capacitor that is set in motion by a signal fed to it from a radio antenna.1 Conventional radio-wave detection methods, even when the hardware is cooled to 5 to 10 K, are less sensitive than the new laser-based method, which has a noise temperature of just 40 mK.
Strongly coupled mechanical vibrations
The detection method works so well because the nanomechanical vibrations of the capacitor (which is placed in a vacuum chamber and biased at a voltage of less than 10 V) are strongly coupled to the optical field of the laser beam.
"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," says Eugene Polzik, professor and head of the research center Quantop at the Niels Bohr Institute at the University of Copenhagen.
The new optomechanical method has three types of noise: Electrical noise in the antenna, mechanical thermal noise in the membrane, and quantum noise of the light. The electrical noise is mostly due to disturbances from the environment. "This has been a technical challenge, and the two PhD students, Tolga Bagci and Anders Simonsen, have worked days and nights to solve the problem. The solution has been to find just the right way to shield the experiment," says research assistant Professor Albert Schliesser, who coordinated the the experiments in Quantop's optomechanical laboratory at the Niels Bohr Institute.
Eugene Polzik and Albert Schliesser see great potential in the new method both in equipment for medical treatment and for observations in space, where cosmologists measure radio radiation to study the infant universe.
Source: http://www.nbi.ku.dk/english/news/news14/ultra-sensitive-detection-of-radio-waves-with-lasers/
REFERENCE:
1. T. Bagci et al., Nature (2014); doi: 10.1038/nature13029