Gérard Roger

Single-shot measurement of a 52-fs pulse

We demonstrate the possibility of a 52-fs pulse single-shot measurement by using the spatial analysis of the second harmonic beam produced in an optical autocorrelator. We show that this method gives means of optimizing low repetition rate femtosecond amplifiers.

Room temperature triggered single-photon source in the near infrared

We report the realization of a solid-state triggered single-photon source with narrow emission in the near infrared at room temperature. It is based on the photoluminescence of a single nickel–nitrogen NE8 colour centre in a chemical vapour deposited diamond nanocrystal. Stable single-photon emission has been observed in the photoluminescence under both continuous-wave and pulsed excitations. The realization of this source represents a step forward in the application of diamond-based single-photon sources to quantum key distribution (QKD) under practical operating conditions.

A New Light on Single Photon Interferences

During the past fifteen years, nonclassical effects in the statistical properties of light have been extensively studied from a theoretical point of view,’ and some have been experimentally demon~trated.~-’*’~ All are related to second-order coherence properties via measurements of intensity correlation functions or of statistical moments. However, there has still been no test of the conceptually very simple situation dealing with single photon states of the light impinging on a beam-splitter. In this case, quantum mechanics predicts a perfect anticorrelation for photodetections on both sides of the beam-splitter, while any description involving classical fields would predict some amount of coincidences. The first purpose of this paper is to report on an experiment close to this ideal situation because we have found a coincidence rate, on both sides of a beam-splitter, five times smaller than the classical lower limit. When it comes to single photon states of the light, it is tempting to revisit the famous historical “single photon interference experiments.”* One then finds that, in spite of their den~minat ion ,~ none has been performed with single photon states of the light. As a matter of fact, all have been carried out with chaotic light for which it is well known that quantum second-order coherence properties cannot be distinguished from classical ones, even with a strongly attenuated beam.” This is why we have carried out an interference experiment with the same apparatus as used in the first experiment, that is, with light for which we have demonstrated a property characteristic of single photon states. This single photon interference experiment will be described in the last part of this paper. We shall first summarize briefly the principle of intensity correlation experiments in which striking differences between semiclassical and quantum treatments of light may appear. Then, we shall introduce a simple “anticorrelation” criterion for a nonclassical behavior of light. Eventually, we shall describe the observation of that anticorrelation effect and the single photon interference experiment.

Three-dimensional time-resolved fluorescence imaging by multifocal multiphoton microscopy for a photosensitizer study in living cells

Two-photon fluorescence microscopy is widely applied to biology and medicine to study both the structure and dynamic processes in living cells. The main issue is the slow acquisition rate due to the point scanning approach limiting the multimodal detection (x, y, z, t). To extend the performances of this powerful technique, we present a time-resolved multifocal multiphoton microscope (MMM) based on laser amplitude splitting. An array of 8 x 8 foci is created on the sample that gives a direct insight of the fluorescence localization. Four-dimensional (4D) imaging is obtained by combining simultaneous foci scanning, time-gated detection, and z displacement. We illustrate time-resolved MMM capabilities for 4D imaging of a photosensitizer inside living colon cancer cells. The aim of this study is to have a better understanding of the photophysical processes implied in the photosensitizer reactivity.

Quantum beats in continuously excited atomic cascades

Abstract We report on the observation of strong Zeeman beats in the temporal correlation between the two photons emitted in the 4p21 S0 → 4s 4p 1 P1 → 4s21 S0 cascade in calcium. These beats result from a quantum interference between the various decaying channels. Unlike usual quantum beats, they are observed with a continuous excitation of the upper level.

Single shot measurement of the optical Kerr effect kinetics

We present a method allowing measurement of the kinetics of the optical Kcrr effect in transparent media using a single femtosecond pulse. This method is based on a spectrotemporal transformation. We describe the experimental results obtained for ultrafast and noninstantaneous responses.

20 fs amplified pulses

Abstract We describe the production of 20 fs, a few microjoule pulses using amplification and compression of 80 fs pulses spectrally broadened by self-phase modulation in an optical fiber.

Time-resolved multifocal multiphoton microscopy

Two photon microscopy is a powerful tool for cells or tissues imaging. However it presents the drawback of being a laser-scanning technique leading to long time acquisition for 3D images. To preserve biological samples from too long experiments and provide a more complete spectroscopic tool we developed a time-resolved multifocal multiphoton microscope. This setup allows us to speed up the acquisition and gives both intensity and lifetime images for all multifocal points.

EDFAs with improved gain-flatness owing to a new pump design

A new pump source based on a semiconductor array coupled with an external cavity laser is shown. Its broad output spectrum allows to improve the EDFA gain flatness while reducing manufacturing cost.

Multifocal multiphoton fluorescence lifetime microscopy for biomedical applications

Two-photon microscopy is a key method for biological and medical research on cells and tissues mainly due to the submicronic spatial resolution. Unfortunately in its conventional form, this technique leads to long time recording for three-dimensional and fluorescence lifetime imaging because it requires a single point laser scanning. The most suitable way to improve acquisition time is to illuminate the biological sample with several excitation points simultaneously. We thus present a time-resolved multifocal multiphoton microscope. Besides the advantage of preserving biological samples by reducing by a factor 64 the exposition time, this method keeps also the possibility of measuring both intensity and lifetime images of the samples.