M. Peiris

Coherent versus incoherent light scattering from a quantum dot

We analyze the light scattered by a single InAs quantum dot interacting with a resonant continuous-wave laser. High resolution spectra reveal clear distinctions between coherent and incoherent scattering, with the laser intensity spanning over four orders of magnitude. We find that the fraction of coherently scattered photons can approach unity under sufficiently weak or detuned excitation, ruling out pure dephasing as a relevant decoherence mechanism. We show how spectral diffusion shapes spectra, correlation functions, and phase-coherence, concealing the ideal radiatively-broadened two-level system described by Mollow.

Franson Interference Generated by a Two-Level System

We report a Franson interferometry experiment based on correlated photon pairs generated via frequency-filtered scattered light from a near-resonantly driven two-level semiconductor quantum dot. In contrast to spontaneous parametric down-conversion and four-wave mixing, this approach can produce single pairs of correlated photons. We have measured a Franson visibility as high as 66%, which goes beyond the classical limit of 50% and approaches the limit of violation of Bells inequalities (70.7%).

Isotopic gas analysis through Purcell cavity enhanced Raman scattering

Purcell enhanced Raman scattering (PERS) by means of a doubly resonant Fabry-Perot microcavity (mode volume ≈ 100 μm3 and finesse ≈ 30 000) has been investigated as a technique for isotopic ratio gas analysis. At the pump frequency, the resonant cavity supports a buildup of circulating power while simultaneously enabling Purcell spontaneous emission rate enhancement at the resonant Stokes frequency. The three most common isotopologues of CO2 gas were quantified, and a signal was obtained from 13C16O2 down to a partial pressure of 2 Torr. Due to its small size and low pump power needed (∼10 mW) PERS lends itself to miniaturization. Furthermore, since the cavity is resonant with the emission frequency, future improvements could allow it to serve as its own spectral analyzer and no separate spectroscopic device would be needed.

Solid optical ring interferometer for high-throughput feedback-free spectral analysis and filtering

We describe a simple and inexpensive optical ring interferometer for use in high-resolution spectral analysis and filtering. It consists of a solid cuboid, reflection-coated on two opposite sides, in which constructive interference occurs for waves in a rhombic trajectory. Due to its monolithic design, the interferometers resonance frequencies are insensitive to environmental disturbances over time. Additional advantages are its simplicity of alignment, high-throughput, and feedback-free operation. If desired, it can be stabilized with a secondary laser without disturbance of the primary signal. We illustrate the use of the interferometer for the measurement of the spectral Mollow triplet from a quantum dot and characterize its long-term stability for filtering applications.

Correlations in pulsed resonance fluorescence

We investigated the first and second-order correlations of the light scattered near-resonantly by a quantum dot under excitation by a frequency comb, i.e., a periodically pulsed laser source. In contrast to its monochromatic counterpart, the pulsed resonance fluorescence spectrum features a superposition of sidebands distributed around a central peak with maximal sideband intensity near the Rabi frequency. Distinguishing between the coherently and incoherently scattered light reveals pulse-area dependent Rabi oscillations evolving with different phase for each component. Our observations, which can be reproduced theoretically, may impact schemes for remote entanglement based on pulsed two-photon interference.

Dynamics of light-induced thermomechanical mirror deformations in high-finesse Fabry–Perot microresonators

Light recirculating inside an optical resonator can spontaneously trigger persistent cyclical thermomechanical mirror deformations. We have observed and characterized the dynamics of such deformations in high-finesse Fabry–Perot microcavities built following three distinct designs. The designs differed in form factor and confinement geometry, incorporating either (A) two nominally planar bulk mirrors, (B) one planar and one microconcave bulk mirror, or (C) one microconcave bulk mirror and one microconcave mirror at the tip of an optical fiber. For all cases, the cavity transmission exhibited bistability and high-frequency (∼MHz), high-amplitude pulsations for input powers greater than ≈10  mW at a cavity finesse of ≈30000. A theoretical analysis reveals that these pulsations are the result of the competition between photothermal expansion and photothermal refraction in the mirror coatings that induces “slow-fast” dynamics. We model these dynamics for the three different cavities and show that their varying duty cycles and periods are consistent with light-induced heating and heat dissipation conforming to the cavity mode spot size and the mechanical mirror support structure.

Erratum: Franson Interference Generated by a Two-Level System [Phys. Rev. Lett. 118 , 030501 (2017)]

This corrects the article DOI: 10.1103/PhysRevLett.118.030501.

Two-photon spectrum of the light scattered by a quantum dot

We report the measurement of the two-photon spectrum of the light scattered by a single InAs quantum dot interacting with a strong near-resonant monochromatic laser.

Resonance fluorescence spectrum from a quantum dot driven by a periodically-pulsed laser

We report the measurement of the resonance fluorescence spectrum from a quantum dot under periodically-pulsed excitation. The evolution of multiple sidebands and Rabi oscillations for coherently and incoherently scattered light were observed.

Laser-Induced Fluorescence from N2+ Ions Generated by a Corona Discharge in Ambient Air

In this work, we present the measurement of laser-induced fluorescence from N2+ ions via the B2Σ+ u − X2Σ+ g band system in the near-ultraviolet. The ions were generated continuously by a plasma glow discharge in low pressure N2 and by a corona discharge in ambient air. The fluorescence decay time was found to rapidly decrease with increasing pressure leading to an extrapolated decay rate of ≈10 10 s−1 at atmospheric pressure. In spite of this quenching, we were able to observe laser induced fluorescence in ambient air by means of a time-gated spectral measurement. In the process of comparing the emission signal with that of N2 spontaneous Raman scattering, ion concentrations in ambient air of order 10 8 -10 10 cm−3 were determined. With moderate increases in laser power and collection efficiency, ion concentrations of less than 10 6 cm−3 may be measurable, potentially enabling applications in atmospheric standoff detection of ionizing radiation from hazardous radioactive sources.