Superradiant Atomic Beam Laser


Steady-state superradiant lasers are a promising candidate for next-generation ultracoherent light sources. In this thesis, we propose a new type of superradiant laser based on a hot atomic beam traversing an optical cavity. We show that the theoretical minimum linewidth and maximum power are competitive with the best ultracoherent clock lasers. Also, our system operates naturally in a continuous wave modality, which has been elusive for superradiant lasers so far. Unlike many existing proposals for ultracoherent lasers, our design is simple and rugged. This makes it a potential candidate for the  first widely accessible ultracoherent laser, as well as the first to realize sought-after applications of ultracoherent lasers in challenging environments. Aside from metrological usefulness, the superradiant atom beam laser system is of fundamental interest in terms of various superradiant phase transitions. To this end, we theoretically analyze the system for three different configurations: (i) For a thermal atomic beam interacting with a resonant cavity mode, we derive a semiclassical model and determine the onset of superradiant emission and its stability. We find two different superradiant phases; a steady-state superradiant phase and a multi-component superradiant phase. In the latter case we observe sidebands in the frequency spectrum that can be calculated using a stability analysis of the amplitude mode of the collective dipole. We show that both superradiant phases are robust against free-space spontaneous emission and T2 dephasing processes. (ii) For a collimated atomic beam interacting with an off-resonant cavity mode, we derive an analytical formula for the cavity pulling coefficient. We find that the pulling is small if the cavity linewidth is much larger than the collective linewidth of the atomic beam. This regime is desired for building stable lasers because the emission frequency is robust against cavity length fluctuations. Furthermore, we find polychromatic emission regimes, where the spectrum has several frequency components while the light output is still superradiant. (iii) For a slanted collimated atomic beam passing through a cavity that is on resonance, we find that the atoms undergo superradiant emission when the collective linewidth exceeds the transit-time broadening. We  find steady-state superradiance providing the tilt of the atomic beam is sufficiently small. However, if the atoms travel more than half a wavelength along the cavity axis during one transit time we predict a dynamical phase transition to a new bistable superradiant regime. In this phase the atoms undergo collective spontaneous emission with a frequency that can be either blue or red detuned from the free-space atomic resonance. We show that the linewidth of the emitted light exhibits features of a critical scaling close to the phase boundaries

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Department of Physics
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University of Colorado Boulder
Boulder, CO
JILA PI Advisors
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