Higher-order photon correlations in pulsed photonic crystal nanolasers

We report on the higher-order photon correlations of a high-$\beta$ nanolaser under pulsed excitation at room temperature. Using a multiplexed four-element superconducting single photon detector we measured g$^{(n)}(\vec{0})$ with $n$=2,3,4. All orders of correlation display partially chaotic statistics, even at four times the threshold excitation power. We show that this departure from coherence and Poisson statistics is due to the quantum fluctuations associated with the small number of dipoles and photons involved in the lasing process

Les solitons de cavité (étude expérimentale)

L étude expérimentale des structures spatiales localisées indépendantes et contrôlables nommées solitons de cavité dans une cavité semi-conductrice, constitue le cadre du travail présenté dans ce mémoire. Cette étude qui repose sur une expérience d injection optique dans le plan transverse d un laser semi-conducteur à cavité verticale (VCSEL), nous a permis de définir les régions de paramètres où ces structures existent, ainsi que les différentes caractéristiques de leur allumage aussi bien spontané que contrôlé. La possibilité de définir leurs positions ainsi que celle de les mouvoir en utilisant un faisceau d injection composé de franges d interférences ou possédant un gradient de phase, a aussi été démontrée. Dans le but de pouvoir contrôler le transitoire de ces structures, une étude sur celui des lasers de classe B a été réalisée. La suppression du pic de surintensité, des oscillations de relaxations et la réduction du temps de retard présent lors de ce transitoire ont été réalisées de manière expérimentale, en utilisant une technique basée sur la connaissance de l espace de phase de ces lasers.The experimental study of independent and controllable spatially localized structures ( cavity solitons ) in a semiconductor cavity constitutes the body of work presented in this thesis. This study, based on optical injection in the transverse plane of vertical cavity semiconductor laser (VCSEL), has permitted us to define the regions in parameter space where these structures exist. We have also determined the different characteristics of their spontaneous as well as controlled switch-on. In addition, we have demonstrated the feasibility of defining their positions as well as moving them by using an injection beam composed of interference fringes or having a phase gradient. With the goal of controlling the transients of these structures, we have studied transient effects in class B lasers. By exploiting our knowledge of the phase space of these lasers, we studied experimentally the suppression of the overshoot peak, relaxation oscillations and the reduction of the retardation time present in these transients.NICE-BU Sciences (060882101) / SudocSudocFranceF

Efficient illumination for microsecond tracking microscopy.

The possibility to observe microsecond dynamics at the sub-micron scale, opened by recent technological advances in fast camera sensors, will affect many biophysical studies based on particle tracking in optical microscopy. A main limiting factor for further development of fast video microscopy remains the illumination of the sample, which must deliver sufficient light to the camera to allow microsecond exposure times. Here we systematically compare the main illumination systems employed in holographic tracking microscopy, and we show that a superluminescent diode and a modulated laser diode perform the best in terms of image quality and acquisition speed, respectively. In particular, we show that the simple and inexpensive laser illumination enables less than 1 μs camera exposure time at high magnification on a large field of view without coherence image artifacts, together with a good hologram quality that allows nm-tracking of microscopic beads to be performed. This comparison of sources can guide in choosing the most efficient illumination system with respect to the specific application

Laser illumination: effect of the current modulation.

<p>A) Beads of 1 m diameter stuck on the glass surface are illuminated by the free running laser biased above threshold (at a current of 96 mA). The coherent noise severely degrades the image quality. B) Same field of view as in A), with bias current modulated by a sinusoidal signal of 80 mA, 2 MHz. Exposure time  =  20 s.</p

Comparison of the modulated laser and SLD illumination.

<p>Image range (maximum and minimum pixel values) are shown as a function of the exposure time for the modulated laser (blue) and the SLD (red) illuminating the same object (one 1 m bead out of focus). The insets show example images obtained at the exposure time indicated; their grey levels are all fixed within the interval (0, 255) to show under-exposure and saturation. The two sources were focused to illuminate evenly the same field of view, and delivered maximum intensity (laser: 120 mW, sinusoidal modulation of 3 at 2 MHz; SLD: 5 mW).</p

Tracking at 1 s exposure.

<p>Z trajectories of a stuck bead tracked while moving the objective in steps of 100 nm. The traces are vertically offset for clarity. Acquisition rate: 3000 fps, exposure time: 1 s.</p

Comparison of the illumination sources.

<p>The six sources are compared in terms of attainable exposure time and relative image quality. The latter is quantified relatively to the SLD source, which gives the best image quality. In the vertical axis we plot the average distance of the images obtained with each source from the images obtained with the SLD (see Methods).</p

Optical spectra of the illumination sources considered and effect of laser current modulation.

<p>A) Optical spectrum of the free running laser diode as a function of the DC bias current. The figure is divided between laser emission (above the threshold current of 60 mA) and amplified spontaneous emission (ASE) below threshold. B) Spectrum of the modulated laser as a function of the modulation frequency (laser DC current: 120 mA, AC modulation: 120 mA, square wave). Each optical spectrum is integrated over a 0.5 s time-window. The color code is the same in A and B. C) Normalized spectra of the SLD, LED, and white lamp (whose spectrum is flat in the visualized region).</p

Quantifying fringe visibility and image noise.

<p>A) Example showing the results of the angular average algorithm used to extract signal, fringe visibility and local image noise from the raw images. The raw image shown is obtained with the unmodulated laser at m. The signal is obtained averaging the raw image rotated in 100 steps around its center (determined with sub-pixel resolution). The image noise is obtained subtracting the signal from the raw image. B) Fringe visibility (defined in the radial intensity profile by the difference of the second maximum with the first minimum), C) noise (defined as the standard deviation of the image noise), and D) visibility-to-noise ratio are shown for the different sources at different axial z-positions.</p