German scientists set new record by developing the sharpest laser ever

Scientists in Germany have developed the sharpest laser in the world. The laser has been built with record braking precision that can help make optical atomic clocks more precise as well as test Einstein’s theory of relativity. The researchers from Physikalisch-Technische Bundesanstalt (PTB) have developed a laser with linewidth of only 10 mHz. In theory, laser light has only one colour, frequency or wavelength. In practice, the spectrum of most types of lasers can, however, reach from a few kHz to a few MHz in width, which is not good enough for numerous experiments requiring high precision. The scientists had to set up two such laser systems so that a comparison could confirm the outstanding properties of the emitted light. The core piece of each of the lasers is a 21-cm long Fabry-Pérot silicon resonator.  The laser’s frequency stability – and thus its linewidth – then depends only on the length stability of the Fabry-Pérot resonator. The scientists at PTB had to isolate the resonator nearly perfectly from all environmental influences which might change its length. They have attained such perfection in doing so that the only influence left was the thermal motion of the atoms in the resonator. This “thermal noise” corresponds to the Brownian motion in all materials at a finite temperature, and it represents a fundamental limit to the length stability of a solid. For this reason, the scientists of this collaboration manufactured the resonator from single-crystal silicon which was cooled down to a temperature of -150 °C. This new type of laser closer to the ideal laser than ever before and can help in understanding  **optical atomic clocks** , precision spectroscopy, **radioastronomy** and for testing the theory of relativity. “The smaller the linewidth of the laser, the more accurate the measurement of the atom’s frequency in an optical clock. This new laser will enable us to decisively improve the quality of our clocks,” said Thomas Legero, a PTB physicist. At PTB, the ultrastable light from these lasers is already being distributed via optical waveguides and is then used by the optical clocks in Braunschweig.