One million (paper) satellites.

Radiofrequency filings warn of more congestion in space, but also offer possible remedies.

To make a mirrorless laser.

Periodic temporal modulation of a photonic crystal can be used to produce laser light.

Measurement of Penrose Superradiance in a Photon Superfluid.

The superradiant amplification in the scattering from a rotating medium was first elucidated by Sir Roger Penrose over 50 years ago as a means by which particles could gain energy from rotating black holes. Despite this fundamental process being ubiquitous also in wave physics, it has only been observed once experimentally, in a water tank. Here, we measure this amplification for a nonlinear optics experiment in the superfluid regime.

Penrose Superradiance in Nonlinear Optics.

Particles or waves scattered from a rotating black hole can be amplified through the process of Penrose superradiance, although this cannot currently be observed in an astrophysical setting. Here we theoretically show that analog Penrose superradiance arises naturally in the field of nonlinear optics. A loosely focused signal beam can experience gain or amplification as it glances off a strong vortex pump beam in a nonlinear defocusing medium.

High peak power, sub-ps green emission in a passively mode locked W-cavity VECSEL.

We report on the experimental results of a passively mode-locked vertical external cavity surface emitting laser (VECSEL), implemented in a W-cavity configuration, using a lithium triborate (LBO) crystal for intra-cavity second harmonic generation (SHG) at 528 nm. The W-cavity configuration allows separation of the crystal from the semiconductor saturable absorber mirror (SESAM), enabling independent control over the Gaussian beam sizes at the crystal, chip, and SESAM. This optimized cavity demonstrated a second harmonic pulse width of ~760 fs at a frequency of 465 MHz and 230 mW average output power, resulting in a peak pulse power of 580 W.

Quantum Time Crystals and Interacting Gauge Theories in Atomic Bose-Einstein Condensates.

We study the dynamics of a Bose-Einstein condensate trapped circumferentially on a ring, and which is governed by an interacting gauge theory. We show that the associated density-dependent gauge potential and concomitant current nonlinearity permits a ground state in the form of a rotating chiral bright soliton. This chiral soliton is constrained to move in one direction by virtue of the current nonlinearity, and represents a time crystal in the same vein as Wilczek's original proposal.

Observation of Photon Droplets and Their Dynamics.

We present experimental evidence of photon droplets in an attractive (focusing) nonlocal nonlinear medium. Photon droplets are self-bound, finite-sized states of light that are robust to size and shape perturbations due to a balance of competing attractive and repulsive forces. It has recently been shown theoretically, via a multipole expansion of the nonlocal nonlinearity, that the self-bound state arises due to competition between the s-wave and d-wave nonlinear terms, together with diffraction.

Generation of high-power spatially structured beams using vertical external cavity surface emitting lasers.

In this paper, we demonstrate the generation of high-power and spatially structured beams using vertical external cavity surface emitting lasers (VECSEL). At the fundamental wavelength, an intracavity mode-control element is first employed to generate a range of Hermite-Gaussian (HG) modes in a linear cavity. The same HG modes are then excited and frequency doubled in a V-cavity geometry to generate a rich variety of high-power spatially structured beams.

Erratum: Nonlinear Zel'dovich Effect: Parametric Amplification from Medium Rotation [Phys. Rev. Lett. 118, 093901 (2017)].

This corrects the article DOI: 10.1103/PhysRevLett.118.

Nonlinear Zel'dovich Effect: Parametric Amplification from Medium Rotation.

The interaction of light with rotating media has attracted recent interest for both fundamental and applied studies including rotational Doppler shift measurements. It is also possible to obtain amplification through the scattering of light with orbital angular momentum from a rotating and absorbing cylinder, as proposed by Zel'dovich more than forty years ago. This amplification mechanism has never been observed experimentally yet has connections to other fields such as Penrose superradiance in rotating black holes.

Optical analogues of the Newton-Schrödinger equation and boson star evolution.

Many gravitational phenomena that lie at the core of our understanding of the Universe have not yet been directly observed. An example in this sense is the boson star that has been proposed as an alternative to some compact objects currently interpreted as being black holes. In the weak field limit, these stars are governed by the Newton-Schrodinger equation.

Rotation of two trapped microparticles in vacuum: observation of optically mediated parametric resonances.

We demonstrate trapping and rotation of two mesoscopic particles in vacuum using a spatial-light-modulator-based approach to trap more than one particle, induce controlled rotation of individual particles, and mediate interparticle separation. By trapping and rotating two vaterite particles, we observe intensity modulation of the scattered light at the sum and difference frequencies with respect to the individual rotation rates. This first demonstration of optical interference between two microparticles in vacuum leads to a platform to potentially explore optical binding and quantum friction effects.

Non-collinear interaction of photons with orbital angular momentum.

We study the nonlinear interaction between two non-collinear light beams that carry orbital angular momentum (OAM). More specifically, two incident beams interact at an angle in a medium with a second order nonlinearity and thus generate a third, non-collinear beam at the second harmonic frequency that experiences a reduced conversion efficiency in comparison to that expected based on conventional phase-matching theory. This reduction scales with the input beam OAM and, differently from previous spiral bandwidth calculations, is due to a geometric effect whereby the input OAM is projected along the non-collinear interaction direction.

Dynamics of microparticles trapped in a perfect vortex beam.

We analyze microparticle dynamics within a "perfect" vortex beam. In contrast to other vortex fields, for any given integer value of the topological charge, a "perfect" vortex beam has the same annular intensity profile with fixed radius of peak intensity. For a given topological charge, the field possesses a well-defined orbital angular momentum density at each point in space, invariant with respect to azimuthal position.

An interacting dipole model to explore broadband transverse optical binding.

The demonstration of optical binding of micro-particles placed in intense optical fields has resulted in unique and exciting prospects for studying new forms of condensed matter. The ability to tailor optical fields in the spatial and temporal domains elicits the possibility of creating novel condensed matter with the structure controlled by tailoring the optical field. Here, we theoretically calculate the transverse optical binding forces for nanoparticles within monochromatic and broadband optical fields.

Experimental tests of the new paradigm for laser filamentation in gases.

Since their discovery in the mid-1990s, ultrafast laser filaments in gases have been described as products of a dynamic balance between Kerr self-focusing and defocusing by free electric charges that are generated via multiphoton ionization on the beam axis. This established paradigm has been recently challenged by a suggestion that the Kerr effect saturates and even changes sign at high intensity of light and that this sign reversal, not free-charge defocusing, is the dominant mechanism responsible for the extended propagation of laser filaments. We report qualitative tests of the new theory based on electrical and optical measurements of plasma density in femtosecond laser filaments.

The dark spots of Arago.

We explore the diffraction and propagation of Laguerre- Gaussian beams of varying azimuthal index past a circular obstacle both experimentally and numerically. When the beam and obstacle centers are aligned the famous spot of Arago, which arises for zero azimuthal index, is replaced for non-zero azimuthal indices by a dark spot of Arago, a simple consequence of the conserved phase singularity at the beam center. We explore how the dark spot of Arago behaves as the beam and obstacle centers are progressively misaligned, and find that the central dark spot may break into several dark spots of Arago for higher incident azimuthal index beams.

Stability and transient effects in nanosecond ultraviolet light filaments in air.

We investigate the transient behavior and stability of nanosecond duration ultraviolet pulses propagating in air. Both the transient behavior arising from the finite pulse duration and the modulational instability, are found to cause pulses to fragment over lengths on the scale of meters. We discuss the theoretical and experimental implications of the instability and transient effects for long duration pulse propagating in air and generating filaments.

Mode properties of an external-cavity laser with Gaussian gain.

We analyze the mode properties of a laser with a Gaussian gain profile by using the beam propagation method. The resonance properties of the Petermann K factor and the M2 beam quality are shown to be related in the vicinity of degenerate cavity geometries. K is unity for a confocal cavity, even under conditions with strong gain guiding, while M2 is a maximum.

Feshbach-resonance-induced atomic filamentation and quantum pair correlation in atom-laser-beam propagation.

We study the propagation of an atom laser beam through a spatial region with a magnetic field tuned around a Feshbach resonance. Magnetic fields below the resonance produce an effective focusing Kerr medium that causes a modulational instability of the atomic beam. Under appropriate circumstances, this results in beam breakup and filamentation seeded by quasiparticle fluctuations and in the generation of correlated atomic pairs.