1.5     μ m Lasers with Sub-10 mHz Linewidth

We report on two ultrastable lasers each stabilized to independent silicon Fabry-Pérot cavities operated at 124 K. The fractional frequency instability of each laser is completely determined by the fundamental thermal Brownian noise of the mirror coatings with a flicker noise floor of 4×10^{-17} for integration times between 0.8 s and a few tens of seconds. We rigorously treat the notorious divergences encountered with the associated flicker frequency noise and derive methods to relate this noise to observable and practically relevant linewidths and coherence times. The individual laser linewidth obtained from the phase noise spectrum or the direct beat note between the two lasers can be as small as 5 mHz at…

• UD
  U.S. Department of Defense
• AV
  Alexander von Humboldt-Stiftung
• EA
  European Association of National Metrology Institutes
• NI
  National Institute of Standards and Technology
• H2
  Horizon 2020 Framework Programme

  Award: 15SIB03 OC18