arXiv subjects

E. C. Le Ru

Publications and source records attributed to E. C. Le Ru.

9 recordsLinked to original sources

arXiv2016

SMARTIES: user-friendly codes for fast and accurate calculations of light scattering by spheroids

We provide a detailed user guide for SMARTIES, a suite of Matlab codes for the calculation of the optical properties of oblate and prolate spheroidal particles, with comparable capabilities and ease-of-use as Mie theory for spheres. SMARTIES is a Matlab implementation of an improved T-matrix algorithm for the theoretical modelling of electromagnetic scattering by particles of spheroidal shape. The theory behind the improvements in numerical accuracy and convergence is briefly summarised, with reference to the original publications. Instructions of use, and a detailed description of the code structure, its range of applicability, as well as guidelines for further developments by advanced users are discussed in separate sections of this user guide. The code may be useful to researchers seeking a fast, accurate and reliable tool to simulate the near-field and far-field optical properties of elongated particles, but will also appeal to other developers of light-scattering software seeking a reliable benchmark for non-spherical particles with a challenging aspect ratio and/or refractive index contrast.

physics.optics↗

arXiv2008

Evidence of natural isotopic distribution from single-molecule SERS

We report on the observation of the natural isotopic spread of carbon from single-molecule Surface Enhanced Raman Spectroscopy (SM-SERS). By choosing a dye molecule with a very localized Raman active vibration in a cyano bond (C$\equiv$N triple bond), we observe (in a SERS colloidal liquid) a small fraction of SM-SERS events where the frequency of the cyano mode is softened and in agreement with the effect of substituting $^{12}$C by the next most abundant $^{13}$C isotope. This example adds another demonstration of single molecule sensitivity in SERS through isotopic editing which is done, in this case, not by artificial isotopic editing but rather by nature itself. It also highlights SERS as a unique spectroscopic tool, capable of detecting an isotopic change in one atom of a single molecule.

cond-mat.soft↗

arXiv2006

Enhancement factor distribution around a single SERS Hot-spot and its relation to Single Molecule detection

We provide the theoretical framework to understand the phenomenology and statistics of single-molecule (SM) signals arising in Surface-Enhanced Raman Scattering (SERS) under the presence of so-called electromagnetic hot-spots (HS's). We show that most characteristics of the SM-SERS phenomenon can be tracked down to the presence of tail-like (power law) distribution of enhancements and we propose a specific model for it. We analyze, in the light of this, the phenomenology of SM-SERS and show how the different experimental manifestations of the effect reported in the literature can be analyzed and understood under a unified ``universal'' framework with a minimum set of parameters.

physics.chem-ph↗

arXiv2006

On the Experimental Estimation of Surface Enhanced Raman Scattering (SERS) Cross Sections by Vibrational Pumping

We present an in-depth analysis of the experimental estimation of cross sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented.

physics.chem-ph↗

arXiv2005

A conclusive demonstration of vibrational pumping and determination of SERS cross sections

We provide conclusive demonstration of vibrational pumping under Surface Enhanced Raman Scattering (SERS) conditions by performing anti-Stokes/Stokes ratio measurements down to 10 K using dried silver colloids, the dye rhodamine 6G and 676 nm laser excitation. The method we propose allows the measurement of the SERS cross sections for different modes and the determination of the asymmetry between the anti-Stokes and Stokes SERS cross sections.

physics.chem-ph↗

arXiv2005

Temperature dependent anti-Stokes/Stokes ratios under Surface Enhanced Raman Scattering (SERS) conditions

We make systematic measurements of Raman anti-Stokes/Stokes (aS/S) ratios using two different laser excitations (514 and 633 nm) of rhodamine 6G (RH6G) on dried Ag colloids over a wide range of temperatures (100 to 350 K). We show that a temperature scan allows the separation of the contributions to the aS/S ratios from {\it resonance effects} and {\it heating/pumping}, thus decoupling the two main aspects of the problem. The temperature rise is found to be larger when employing the 633 nm laser. In addition, we find evidence for mode specific vibrational pumping at higher laser power densities. We analyze our results in the framework of ongoing discussion on laser heating/pumping under SERS conditions.

physics.chem-ph↗

arXiv2005

Bi-Analyte Surface Enhanced Raman Scattering for unambiguous evidence of single molecule detection

A method is proposed to pin down an unambiguous proof for single molecule surface enhanced Raman spectroscopy (SERS). The simultaneous use of two analyte molecules enables a clear confirmation of the single (or few) molecule nature of the signals. This method eliminates most of the uncertainties associated with low dye concentrations in previous experiments. It further shows that single-molecule signals are very common in SERS, both in liquids and on dry substrates.

physics.chem-ph↗

arXiv2005

Surface-Enhanced Raman Scattering (SERS) and Surface-Enhanced Fluorescence (SEF) in the context of modified spontaneous emission

Surface Enhanced Raman Scattering (SERS) and Surface-Enhanced Fluorescence (SEF) are studied within the framework of modified Spontaneous Emission (SE), and similarities and differences are highlighted. This description sheds new light into several aspects of the SERS electromagnetic enhancement. In addition, combined with the optical reciprocity theorem it also provides a rigorous justification of a generalized version of the widely used SERS enhancement factor proportional to the fourth power of the field ($|E|^4$). We show, in addition, that this approach also applies to the calculation of Surface-Enhanced Fluorescence cross-sections thus presenting both phenomena SERS and SEF within a unified framework.

physics.chem-ph↗

arXiv2005

Plasmon-mediated Polarization Anomalies in Surface Enhanced Raman Scattering (SERS)

We discuss the effect of the local field polarization in metallic nanostructures where large field enhancements can be induced by excitation of localized surface plasmons. To demonstrate the importance of these effects, we study a few model systems in 2D and 3D. As an experimental probe of this effect, we suggest to use depolarization ratios in Surface Enhanced Raman Spectroscopy (SERS) measurements. We attempt to relate the polarization of the local field to the depolarization ratios in SERS conditions. This approach could also lead to some better understanding of the SERS mechanisms at a microscopic level.

physics.chem-ph↗