Scientists have developed the world’s sharpest laser with record-breaking precision that can help make optical atomic clocks more precise as well as test Einstein’s theory of relativity. Theoretically, laser light has only one colour, frequency or wavelength. In reality, however, there is always a certain linewidth. Researchers, including those from the Physikalisch- Technische Bundesanstalt (PTB) in Germany have now developed a laser with a linewidth of only 10 miliHertz (mHz) – closer to the ideal laser than ever before. This precision is useful for various applications such as optical atomic clocks, precision spectroscopy, radio astronomy and for testing the theory of relativity.
More than 50 years have passed since the first technical realisation of the laser, and we cannot imagine how we could live without them today. Laser light is used in numerous applications in industry, medicine and information technologies. Lasers have brought about a real revolution in many fields of research and in metrology – or have even made some new fields possible in the first place.
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One of a laser’s outstanding properties is the excellent coherence of the emitted light. For researchers, this is a measure for the light wave’s regular frequency and linewidth. Ideally, laser light has only one fixed wavelength or frequency. 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.
Research has therefore focused on developing ever better lasers with greater frequency stability and a narrower linewidth. Within the scope of a nearly 10-year-long joint project with researchers from from JILA, a joint institute of the National Institute of Standards and Technology and the University of Colorado Boulder in the US a laser has now been developed at PTB whose linewidth is only 10 mHz (0.01 Hz), hereby establishing a new world record.
“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. In addition to the new laser’s extremely small linewidth, researchers found out by means of measurements that the emitted laser light’s frequency was more precise than what had ever been achieved before.
The new lasers are now being used both at PTB and at JILA in Boulder to further improve the quality of optical atomic clocks and to carry out new precision measurements on ultracold atoms. 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.