P. Tchénio

FIELD ENHANCEMENT AND APERTURELESS NEAR-FIELD OPTICAL SPECTROSCOPY OF SINGLE MOLECULES

We report on fluorescence enhancement in near field optical spectroscopy by apertureless microscopy. Our apertureless microscope is designed around a confocal fluorescence microscope associated with an AFM head. First, we show that the confocal microscope alone allows single molecule imaging and single molecule fluorescence analysis. When associated with the AFM head, we demonstrate, for the first time to our knowledge, that single molecule fluorescence is enhanced under the silicon tip. We tentatively attribute this effect to field enhancement under the tip.

Polarised Raman spectroscopy on a single class of single-wall nanotubes by nano surface-enhanced scattering

Abstract We report on the opportunity of performing polarised Raman spectroscopy on nanotubes by using surface-enhanced Raman scattering (SERS) mechanisms at the scale of a single hot site. In conjunction with the opportunity of selecting a single class of single wall nanotubes (SWNTs), it opens the way to fine spectroscopic studies of carbon nanotubes. Results obtained on a single class of nanotubes demonstrate first that polarised Raman spectroscopy is possible when a single hot site of a SERS substrate is selected and second that in this situation, unambiguous assignment of the modes is possible.

Phase-encoding technique in time-domain holography: theoretical estimation

In previous investigations of optical data storage in persistent spectral-hole-burning materials, either the spectral or the temporal positions of the data were used as memory addresses. We suggest having the address represented by the spectral shape of the writing field and retrieving information with the aid of pattern recognition of this spectral shape. This procedure is expected to accelerate access to the stored data. To evaluate the validity of the method, we consider various physical effects that may give rise to cross talk among the different addresses. A numerical simulation under realistic conditions is presented.

Field cross correlator for analysis of ultrafast signals

The cross-correlation function between two light fields is recorded with the help of a new device. The proposed correlator exhibits ultrashort time resolution. The optical path difference between the two interfering beams does not have to be known with interferometric precision. The experimental dynamic range proved to be as large as 10(5). The device features imaging capabilities that could be applied to the analysis of two-dimensional images with ultrashort time resolution.

Raman hyperspectral imaging applied to chemical co-localization in diluted samples of perylene-doped nanotubes

Raman imaging is known to be an efficient tool to localize different chemical species in a sample. Nevertheless, the signature of a minor compound is hard to retrieve in a dense heterogeneous sample. This paper aims at demonstrating that Raman imaging used in a hyperspectral configuration is still a very efficient tool to extract the signature of traces in heterogeneous samples, if the sample is diluted. It opens the way to study chemical co-localization in the case of minor compounds. This possibility is illustrated in the case of perylene-doped single-wall nanotubes (SWNTs).

Storage of a spectrally shaped hologram in a frequency selective material

A spectral holography experiment is performed in a hole-burning material. A shaping device is used to tailor the spectrum of the pulses which engrave the hologram. The resolution of the spectral shaping technique is investigated both theoretically and experimentally.

Observation of 0π-pulse formation with incoherent light

Observation of 0π-pulse formation with incoherent light through field cross-correlation is theoretically and experimentally demonstrated. The experiment illuminates some of the properties of this new incoherent light technique, which is used to analyze the fast temporal variations of the signal. In particular, the technique’s time resolution, signal-to-noise ratio, and sensivity to dispersion are investigated.

Field cross-correlation of time-delayed DFWM signals for population lifetime measurement with incoherent light

Two techniques are proposed for measurement of population lifetime with incoherent light, based on the recording of the field cross-correlation between two time-delayed DFWM signals. Theoretical calculations predict that such records exhibit the decay of the population with a resolution given by the coherence time of the light, and against a zero background. An experiment is reported, demonstrating the main theoretical predictions. The features and possibilities of the methods are discussed.

Determination of the field cross-correlation between successive pulses in a broadband laser

A field cross-correlator is utilised to determine the duration and coherence time of a synchronously-pumped broadband picosecond dye laser. It is shown that recording the autocorrelation profile of the pulse train delivered by the laser for different lengths of the train gives a sensitive measure of the degree of coherence between the successive laser pulses.

Stochastic excitation and detection of persistent spectral structures

Abstract This work belongs to the time-domain approach of persistent spectral hole burning (PHB). In conventional PHB, a spectral hole is burnt locally inside the absorption band of the sample by monochromatic excitation. In the time domain approach, a spectral hologram is engraved over the entire inhomogeneous width of the band, δI, by a sequence of laser pulses. In an amorphous material the absorption line is so broad that a subpicosecond pulse is needed to read out the engraved spectral structure. We demonstrate that this requirement can be circumvented. In this purpose, an original field cross-correlator is used to detect spectral structures in a sample of polystyrene doped by octaethylporphine molecules when stochastic light is used. We analyze the coherent transient signal with a time resolution given by the coherence time of the probe light which can be as short as 100 fs.