Biomedical subjects

E Rosencher

Publications and source records attributed to E Rosencher.

9 recordsLinked to original sources

PubMed2005

Optical transitions in single-wall boron nitride nanotubes.

Optical transitions in single-wall boron nitride nanotubes are investigated by means of optical absorption spectroscopy. Three absorption lines are observed. Two of them (at 4.45 and 5.5 eV) result from the quantification involved by the rolling up of the hexagonal boron nitride (h-BN) sheet. The nature of these lines is discussed, and two interpretations are proposed. A comparison with single-wall carbon nanotubes leads one to interpret these lines as transitions between pairs of van Hove singularities in the one-dimensional density of states of boron nitride single-wall nanotubes. But the confinement energy due to the rolling up of the h-BN sheet cannot explain a gap width of the boron nitride nanotubes below the h-BN gap. The low energy line is then attributed to the existence of a Frenkel exciton with a binding energy in the 1 eV range.

Journal Article↗

PubMed2004

Mid-infrared high-resolution absorption spectroscopy by use of a semimonolithic entangled-cavity optical parametric oscillator.

By recording low-pressure absorption lines of N2O around 3.9 microm, we fully qualify a pulsed entangled-cavity doubly resonant optical parametric oscillator as a power tool for high-resolution spectroscopy. This compact source runs at a high repetition rate (>10 kHz) with a low threshold of oscillation (<8 microJ), is mode-hop-free tunable over 5 cm(-1), and displays single-frequency Fourier-transformed-limited operation (linewidth <0.005 cm(-1)). A high potential for nonlinear spectroscopy is also expected given the high peak power (70 W) and the good quality (M2 < 2) of the output beam.

Journal Article↗

PubMed2004

Random quasi-phase-matching in bulk polycrystalline isotropic nonlinear materials.

Three-wave mixing in nonlinear materials--the interaction of two light waves to produce a third--is a convenient way of generating new optical frequencies from common laser sources. However, the resulting optical conversion yield is generally poor, because the relative phases of the three interacting waves change continuously as they propagate through the material. This phenomenon, known as phase mismatch, is a consequence of optical dispersion (wave velocity is frequency dependent), and is responsible for the poor optical conversion potential of isotropic nonlinear materials. Here we show that exploiting the random motion of the relative phases in highly transparent polycrystalline materials can be an effective strategy for achieving efficient phase matching in isotropic materials. Distinctive features of this 'random quasi-phase-matching' approach are a linear dependence of the conversion yield with sample thickness (predicted in ref. 3), the absence of the need for either preferential materials orientation or specific polarization selection rules, and the existence of a wavelength-dependent resonant size for the polycrystalline grains.

Journal Article↗

PubMed1996