149 research outputs found
How lasing localized structures evolve out of passive mode locking
We investigate the relationship between passive mode locking and the formation of time-localized structures in the output intensity of a laser. We show how the mode-locked pulses transform into lasing localized structures, allowing for individual addressing and arbitrary low repetition rates. Our analysis reveals that this occurs when (i) the cavity round-trip is much larger than the slowest medium time scale, namely the gain recovery time, and (ii) the mode-locked solution coexists with the zero intensity (off) solution. These conditions enable the coexistence of a large quantity of stable solutions, each of them being characterized by a different number of pulses per round-trip and with different arrangements. Then, each mode-locked pulse becomes localized, i.e., individually addressable. © 2014 American Physical Society.J. J. acknowledges financial support from Ramón y Cajal program and CNRS for supporting a visit at the INLN where part of his work was developed. J. J. and S. B. acknowledge financial support from project RANGER (TEC2012-38864- C03-01) and from Direcció General de Recerca de les Illes Balears cofunded by the European Union FEDER funds. INLN group acknowledges funding from Région PACA with the Projet Volet Général 2011 GEDEPULSEPeer Reviewe
Decoherence and turbulence sources in a long laser
We investigate the turn-on process in a laser cavity where the roundtrip time is several orders of magnitude greater than the active medium timescales. In this long delay limit the electromagnetic field build-up can be mapped experimentally roundtrip after roundtrip. We show how coherence settles down starting from a stochastic initial condition. In the early stages of the turn-on, we show that power drop-outs emerge, persist for several round-trips and seed dark solitons. These latter structures exhibit a chaotic dynamics and emit radiation that can lead to an overall turbulent dynamics depending on the cavity dispersion
Noise-induced broadening of a quantum-dash laser optical frequency comb
Single-section quantum dash semiconductor lasers have attracted much
attention as an integrated and simple platform for the generation of THz-wide
and flat optical frequency combs in the telecom C-band. In this work, we
present an experimental method allowing to increase the spectral width of the
laser comb by the injection of a broadband optical noise from an external
semiconductor optical amplifier that is spectrally overlapped with the quantum
dash laser comb. The noise injection induces an amplification of the side modes
of the laser comb which acquire a fixed phase relationship with the central
modes of the comb. We demonstrate a broadening of the laser comb by a factor of
two via this technique.Comment: 4 pages, 4 figure
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
Direct constraint on the distance of y2 Velorum from AMBER/VLTI observations
In this work, we present the first AMBER observations, of the Wolf-Rayet and
O (WR+O) star binary system y2 Velorum. The AMBER instrument was used with the
telescopes UT2, UT3, and UT4 on baselines ranging from 46m to 85m. It delivered
spectrally dispersed visibilities, as well as differential and closure phases,
with a resolution R = 1500 in the spectral band 1.95-2.17 micron. We interpret
these data in the context of a binary system with unresolved components,
neglecting in a first approximation the wind-wind collision zone flux
contribution. We show that the AMBER observables result primarily from the
contribution of the individual components of the WR+O binary system. We discuss
several interpretations of the residuals, and speculate on the detection of an
additional continuum component, originating from the free-free emission
associated with the wind-wind collision zone (WWCZ), and contributing at most
to the observed K-band flux at the 5% level. The expected absolute separation
and position angle at the time of observations were 5.1±0.9mas and
66±15° respectively. However, we infer a separation of
3.62+0.11-0.30 mas and a position angle of 73+9-11°. Our analysis thus
implies that the binary system lies at a distance of 368+38-13 pc, in agreement
with recent spectrophotometric estimates, but significantly larger than the
Hipparcos value of 258+41-31 pc
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