232 research outputs found
Quantitative test of general theories of the intrinsic laser linewidth
We perform a first-principles calculation of the quantum-limited laser
linewidth, testing the predictions of recently developed theories of the laser
linewidth based on fluctuations about the known steady-state laser solutions
against traditional forms of the Schawlow-Townes linewidth. The numerical study
is based on finite-difference time-domain simulations of the semiclassical
Maxwell-Bloch lasing equations, augmented with Langevin force terms, and thus
includes the effects of dispersion, losses due to the open boundary of the
laser cavity, and non-linear coupling between the amplitude and phase
fluctuations ( factor). We find quantitative agreement between the
numerical results and the predictions of the noisy steady-state ab initio laser
theory (N-SALT), both in the variation of the linewidth with output power, as
well as the emergence of side-peaks due to relaxation oscillations.Comment: 24 pages, 10 figure
Local invariants identify topology in metals and gapless systems
Although topological band theory has been used to discover and classify a
wide array of novel topological phases in insulating and semi-metal systems, it
is not well-suited to identifying topological phenomena in metallic or gapless
systems. Here, we develop a theory of topological metals based on the system's
spectral localizer and associated Clifford pseudospectrum, which can both
determine whether a system exhibits boundary-localized states despite the
presence of degenerate bulk bands and provide a measure of these states'
topological protection even in the absence of a bulk band gap. We demonstrate
the generality of this method across symmetry classes in two lattice systems, a
Chern metal and a higher-order topological metal, and prove the topology of
these systems is robust to relatively strong perturbations. The ability to
define invariants for metallic and gapless systems allows for the possibility
of finding topological phenomena in a broad range of natural, photonic, and
other artificial materials that could not be previously explored.Comment: 10 pages, 4 figure
Generating and processing optical waveforms using spectral singularities
We show that a laser at threshold can be utilized to generate the class of
dispersionless waveforms
at optical frequencies.We derive these properties analytically and demonstrate
them in semiclassical time-domain laser simulations. We then utilize these
waveforms to expand other waveforms with high modulation frequencies and
demonstrate theoretically the feasibility of complex-frequency
coherent-absorption at optical frequencies, with efficient energy transduction
and cavity loading. This approach has potential applications in quantum
computing, photonic circuits, and biomedicine
Quadratic pseudospectrum for identifying localized states
We examine the utility of the quadratic pseudospectrum in photonics and
condensed matter. Specifically, the quadratic pseudospectrum represents a
method for approaching systems with incompatible observables, as it both
minimizes the "eigen-error" in the joint approximate spectrum of the
incompatible observables and does not increase the system's computational
complexity. Moreover, we derive an important estimate relating the Clifford and
quadratic pseudospectra. Finally, we prove that the quadratic pseudospectrum is
local, and derive the bounds on the errors that are incurred by truncating the
system in the vicinity of where the pseudospectrum is being calculated.Comment: 20 pages, 9 figure
Pump-induced Exceptional Points in Lasers
We demonstrate that the above-threshold behavior of a laser can be strongly
affected by exceptional points which are induced by pumping the laser
nonuniformly. At these singularities, the eigenstates of the non-Hermitian
operator which describes the lasing modes coalesce. In their vicinity, the
laser may turn off even when the overall pump power deposited in the system is
increased. Such signatures of a pump- induced exceptional point can be
experimentally probed with coupled ridge or microdisk lasers.Comment: 4.5 pages, 4 figures, final version including additional FDTD dat
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