Abstract
Microlasers, relying on the strong coupling between active particles and optical microcavity, exhibit fundamental differences from conventional lasers, such as multi-threshold/thresholdless behavior and nonclassical photon emission. As light sources, microlasers possess extensive applications in precision measurement, quantum information processing, and biochemical sensing. Here we propose a whispering-gallery-mode microlaser scheme, where ultracold alkaline-earth metal atoms, i.e., gain medium, are tightly confined in a two-color evanescent lattice that is in the ring shape and formed around a microsphere. To suppress the influence of the lattice-induced ac Stark shift on the moderately-narrow-linewidth laser transition, the red-detuned trapping beams operate at a magic wavelength while the wavelength of the blue-detuned trapping beam is set close to the other magic wavelength. The tiny mode volume and high quality factor of the microsphere ensure the strong atom-microcavity coupling in the bad-cavity regime. As a result, both saturation photon and critical atom numbers, which characterize the laser performance, are substantially reduced below unity. We explore the lasing action of the coupled system by using the Monte Carlo approach. Our scheme may be potentially generalized to the microlasers based on the forbidden clock transitions, holding the prospect for microscale active optical clocks in precision measurement and frequency metrology.
Highlights
Microlasers, relying on the strong coupling between active particles and optical microcavity, exhibit fundamental differences from conventional lasers, such as multi-threshold/thresholdless behavior and nonclassical photon emission
The size of a particle-cavity coupled system is usually measured by two dimensionless p arameters[3,10], saturation photon number Nps = γ 2/4g2 and critical particle number Nac = κγ /4g2 with the loss rate κ of intracavity photons, the relaxation rate γ of the laser transition of active particles, and the coupling strength g between one particle and one photon
Various particle-cavity structures have accessed the strong-coupling regime, including one atom/ion/molecule/quantum dot situated in an optical cavity[3,11,12,13], a superconducting qubit interacting with an LC resonator via the electric/magnetic field, and single molecule placed inside a plasmonic nanocavity at room temperature[15]
Summary
Microlasers, relying on the strong coupling between active particles and optical microcavity, exhibit fundamental differences from conventional lasers, such as multi-threshold/thresholdless behavior and nonclassical photon emission. The tiny mode volume and high quality factor of the microsphere ensure the strong atom-microcavity coupling in the bad-cavity regime. As a result, both saturation photon and critical atom numbers, which characterize the laser performance, are substantially reduced below unity. The size of a laser system is significantly suppressed in the strong-coupling limit, Nps, Nac ≪ 1 , where even one photon can saturate the particle’s transition and even one particle can strongly affect the intracavity field. The WGM microcavities are an excellent platform for implementing m icrolasers[19,20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
