40 research outputs found
Tuning random lasing in photonic glasses
We present a detailed numerical investigation of the tunability of a
diffusive random laser when Mie resonances are excited. We solve a multimode
diffusion model and calculate multiple light scattering in presence of optical
gain which includes dispersion in both scattering and gain, without any
assumptions about the parameter. This allows us to investigate a
realistic photonic glass made of latex spheres and rhodamine and to quantify
both the lasing wavelength tunability range and the lasing threshold. Beyond
what is expected by diffusive monochromatic models, the highest threshold is
found when the competition between the lasing modes is strongest and not when
the lasing wavelength is furthest from the maximum of the gain curve
A nanophotonic laser on a graph
Conventional nano-photonic schemes minimise multiple scattering to realise a
miniaturised version of beam-splitters, interferometers and optical cavities
for light propagation and lasing. Here instead, we introduce a nanophotonic
network built from multiple paths and interference, to control and enhance
light-matter interaction via light localisation. The network is built from a
mesh of subwavelength waveguides, and can sustain localised modes and
mirror-less light trapping stemming from interference over hundreds of nodes.
With optical gain, these modes can easily lase, reaching 100 pm
linewidths. We introduce a graph solution to the Maxwell's equation which
describes light on the network, and predicts lasing action. In this framework,
the network optical modes can be designed via the network connectivity and
topology, and lasing can be tailored and enhanced by the network shape.
Nanophotonic networks pave the way for new laser device architectures, which
can be used for sensitive biosensing and on-chip optical information
processing
Modal Coupling of Single Photon Emitters Within Nanofiber Waveguides
Nanoscale generation of individual photons in confined geometries is an
exciting research field aiming at exploiting localized electromagnetic fields
for light manipulation. One of the outstanding challenges of photonic systems
combining emitters with nanostructured media is the selective channelling of
photons emitted by embedded sources into specific optical modes and their
transport at distant locations in integrated systems. Here, we show that
soft-matter nanofibers, electrospun with embedded emitters, combine
subwavelength field localization and large broadband near-field coupling with
low propagation losses. By momentum spectroscopy, we quantify the modal
coupling efficiency identifying the regime of single-mode coupling. These
nanofibers do not rely on resonant interactions, making them ideal for
room-temperature operation, and offer a scalable platform for future quantum
information technology
AC/DC: The FERMI FEL Split and Delay Optical Device for Ultrafast X-ray Science
Free-electron lasers (FELs) are the most advanced class of light-sources, by virtue of their unique capability to lase high-brightness pulses characterized by wavelengths spanning the extreme-ultraviolet, the soft and hard X-ray spectral domains, as well as by temporal lengths lying in the femtosecond (fs) timescale. The next step to push the current standards in ultrafast X-ray science is strongly linked to the possibility of engineering and exploiting time-resolved experiments exclusively for FELs pulses, ideally having different colors tunable at specific electronic resonance of the chemical elements. At the seeded FERMI FEL (Trieste, Italy) this goal is committed to the optical device known as AC/DC, which stands for the auto correlator/delay creator. AC/DC is designed to double the incoming FEL pulse splitting the photon beam by inserting a grazing incidence flat mirror, thus preserving the spectral and temporal properties, and further delaying one of these two pulses in time. It can independently tune the FEL pulses fluence on the two optical paths by means of solid-state filters, too. Here, we present a detailed description about this optical device. Strong emphasis is dedicated to the AC/DC opto-mechanical design and to the laser-based feedback systems implemented to compensate for any mismatch affecting the FEL optical trajectory, ascribable to both mechanical imperfections and paraxial errors rising during a temporal delay scan
A detailed investigation of single-photon laser enabled Auger decay in neon
Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s?2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions
Silk-Based Biocompatible Random Lasing
Biocompatible silk random lasing is obtained by nanostructuring silk proteins into a disordered porous matrix via a self-assembly technique. Lasing action is revealed by spectral narrowing and threshold behavior, and it is sensitive to pH variations in the aqueous environment. Silk random lasing provides a versatile biocompatible system, opening up opportunities for biophotonic applications and biosensing
Percolating plasmonic networks for light emission control
Optical nanoantennas have revolutionised the way we manipulate single photons emitted by individual light sources in a nanostructured photonic environment. Complex plasmonic architectures allow for multiscale light control by shortening or stretching the light wavelength for a fixed operating frequency, meeting the size of the emitter and that of propagating modes. Here, we study self-assembled semi-continuous gold films and lithographic gold networks characterised by large local density of optical state (LDOS) fluctuations around the electrical percolation threshold, a regime where the surface is characterised by large metal clusters with fractal topology. We study the formation of plasmonic networks and their effect on light emission from embedded fluorescent probes in these systems. Through fluorescence dynamics experiments we discuss the role of global long-range interactions linked to the degree of percolation and to the network fractality, as well as the local near-field contributions coming from the local electro-magnetic fields and the topology. Our experiments indicate that local properties dominate the fluorescence modification.Peer ReviewedPostprint (author’s final draft