Hyper Rayleigh Scattering (HRS) is a method allowing the retrieval of metallic nanoparticles morphology. It is usually conducted in a right angle geometry preventing the full determination of all the sample information. To alleviate this problem, we report experiments in this manuscript where we have employed a multi-angle geometry in order to further complement the study. This method is applied to a standard push-pull molecular compound, a well-defined symmetry model system, and then is extended to gold metallic nanoparticles with a diameter of 5 nm. In this way, it is possible to observe how shape deformation, or in other words symmetry, is obtained as compared to the one solely retrieved from the right-angle geometry.
Gliomas are diffuse brain tumors still hardly curable due to the difficulties to identify margins. 5-ALA induced PpIX fluorescence measurements enable to gain in sensitivity but are still limited to discriminate margin from healthy tissue. In this fluorescence spectroscopic study, we compare an expert-based model assuming that two states of PpIX contribute to total fluorescence and machine learning-based models. We show that machine learning retrieves the main features identified by the expert approach. We also show that machine learning approach slightly overpasses expert-based model for the identification of healthy tissues. These results might help to improve fluorescence-guided resection of gliomas by discriminating healthy tissues from tumor margins.
Biopolymers represent natural, renewable and abundant materials. Their use is steadily growing in various areas (food, health, building …) but, in lithography, despite some works, resists, solvents and developers are still oil-based and hazardous chemicals. In this work, we replaced synthetic resist by chitosan, a natural, abundant and hydrophilic polysaccharide. High resolution sub-micron patterns were obtained through chitosan films as water developable, chemically unmodified, positive tone mask resist for an eco-friendly electron beam and deep-UV (193 nm) lithography process. Sub-micron patterns were also successfully obtained using a 248 nm photomasker thanks to the addition of biosourced photoactivator, riboflavin. Patterns were then transferred by plasma etching into silica even for high resolution patterns.
We investigate the quadratic nonlinear optical response from metallic gold nanoparticles homogeneously dispersed in a
medium or deposited on glass substrates. The nanoparticles are prepared by the wet chemistry method in solution used
afterwards. The diameter of the gold nanoparticle is 80 nm. In a homogeneous medium, hyper Rayleigh scattering,
effectively incoherent second harmonic generation is used to determine the origin of the response. It is shown that for 80
nm diameter gold nanoparticles, the overall response stems from the deviation of the shape of the nanoparticle from that
of a perfect sphere and from retardation effects with a similar weight. The latter retardation effects occur because the
diameter of the nanoparticle is no longer vanishing before the wavelength of the incoming electromagnetic field. For
deposited nanoparticles, the sample is illuminated through the transparent glass slide and the light at the harmonic
frequency, produced through the second harmonic generation phenomenon, is observed in the retro-reflection. From the
collected SHG images, it can be unambiguously concluded that the origin of the nonlinearity in 80 nm diameter gold
nanoparticles stems from the substrate influence normal to the interface. It can also be concluded that the gold
nanoparticles can be used to map out the electromagnetic field in the focal volume.
In this paper, the Second Harmonic light intensity scattered off a liquid solution upon illumination by an incident
fundamental frequency beam is written within a general framework in order to describe its coherent and incoherent
contributions. It is shown that this formulation requires the introduction of a correlation function in time, position and
orientation. We discuss this framework in light of recent experiments where the interface and the bulk of liquid solutions
can be investigated simultaneously. We apply here this analysis to a neat water solution to compare the bulk volume and
the interface correlation functions.
Second Harmonic Generation (SHG) a nonlinear optical process sensitive to medium structure deviation from
centrosymmetry has been used to investigate the bulk and the surface of an aqueous phase. Using the combination of
incoherent SHG, also named Hyper Rayleigh Scattering (HRS), and interface coherent SHG, we have investigated the
neat air-water interface. In this paper, we report an analysis where the experimental conditions have been investigated to
have the best contrast between the surface and the volume contributions. Our data are described within a simple model
allowing us to normalize the surface contribution to the volume one.
Second Harmonic Generation (SHG) was used to investigate the two enantiomers of a chiral bridged binaphthol derivative 1(+) and 1(-) at the air-water interface under lateral compression in a Langmuir trough. For each enantiomer, surface pressure and SH intensity were measured simultaneously during compression and decompression cycle of the molecular film. S polarized output SHG intensity as a function of the input polarization angle of the fundamental beam demonstrated the supramolecular origin for the chirality. The formation of 1(+) and 1(-) aggregates in the film was deduced from the non-vanishing SHG intensities collected for the 90° input and S output polarization angles.
Second Harmonic Generation (SHG) was employed to study phase transition in molecular films formed at the air/water interface. Studies were performed at biomimetic lipid monolayers by simultaneous surface tension and SHG measurements. Light polarization analysis of the SHG intensities was performed with different lipid interfaces. A comparison between these interfaces provided lipid condensed state-dependent data. An optical signature was observed in the polarization plots for the transition from the Liquid-Expanded (LE) to the Liquid-Condensed (LC) state.
We report the use of Second Harmonic Generation (SHG) to investigate at the air-water interface molecular films of PL2(-) molecules, a chiral binaphthyl derivative. Under the compression of the monolayer film in a Langmuir trough, large fluctuations of the SHG intensity are observed. From the expressions of the SHG intensity with polarization control of the input fundamental and output harmonic beams, it appears that the intrinsic chirality of the PL2(-) molecule can be disentangled from the supramolecular chirality arising from PL2(-) molecular aggregates. With a careful polarization control of the input and output polarization configurations of the SHG optical set-up, it is then shown that the dominant origin of the observed SHG intensity fluctuations is the formation of PL2(-) molecular aggregates at the air-water interface. The proposed strategy is also suitable for the analysis of the fluctuations in the SHG intensity arising from molecular films at the air-water interface formed from achiral molecular compounds.
The nonlinear optical modulation of a light beam (or Kerr effect) by a single gold metallic nanoparticle has been
obtained by the P-Scan method. The 80 nm diameter gold nanoparticles were spread on a glass substrate and investigated
with a tightly focused femtosecond laser beam at the fundamental wavelength of 840 nm for different incident
intensities. The retro-reflected intensity was recorded in the far field at the same wavelength of 840 nm. Clear deviations
from the linear regime were observed and attributed to both nonlinear refraction and nonlinear absorption of the gold
nanoparticles. Besides, the second harmonic signal was also observed for these nanoparticles allowing for the display of
the linear, quadratic and cubic susceptibility tensors χ(1), χ(2) and χ(3) of the same substrate where are dispersed gold
nanoparticles.
Hyper Rayleigh and Hyper Raman spectra of neat water have been recorded in two different geometrical configurations
where the incident fundamental beam is impinging on the cell at right angle from the collection direction and in retroreflection.
A polarization analysis is also performed for the hyper Rayleigh experiment to underlines the differences in
measuring some elements of the first hyperpolarizability tensor of the molecules present in the liquid solution under
study. These data, beyond the comparison of the cross sections for the different bands observed, allows for a better
insight into the quadratic nonlinear optical response from neat water.
Hyper Rayleigh Scattering (HRS) is an optical process routinely used to measure the first hyperpolarizability of
molecular compounds. In order to investigate the build-up of the first hyperpolarizability of DNA, we report the
investigation of the first hyperpolarizability of two of its constituents, namely the bases Thymine and Adenine at the
fundamental wavelength of 800 nm. In the both cases, the weakness of the HRS signal intensities recorded requires long
acquisition times and statistical analysis of the data to ensure that the sensitivity is reached. For Thymine, the absence of
fluorescence is verified with the recording of the HRS line spectrum. Then, Thymine first hyperpolarizability is
measured and found to be βT = 2.9 x 10-30 esu using a 10 mM concentration aqueous solution. For Adenine, the
problem is complicated by the presence of fluorescence. Hence, we can only determine an upper limit for the first
hyperpolarizability which is set as βA < 4.2 x 10-30 esu.
Second Harmonic Generation (SHG) was used to study the optical properties of molecular films formed at liquid
interfaces (air-water or dodecane-water interfaces). The technique was applied to a two-dimensional film of hemicyanine
molecules: dye (4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide) (DiA) and 4-(4-(diethylamino)styryl)-Nmethylpyridinium iodide (sDiA). First, at the air-water interface, the SHG intensity was measured as a function of the
incident fundamental and outgoing harmonic wave polarization. The orientation of the molecules was determined by the
analysis of the polarization plots. Secondly, the adsorption of sDiA at the dodecane-water interface was characterized by
the SHG technique. Finally, in the case of DiA molecules, the formation of aggregates at the air-water interface was
monitored by the analysis of SHG intensity fluctuations.
Hyper Rayleigh Scattering (HRS) is used to determine the absolute first hyperpolarizability of gold nanorods with an
aspect ratio of 2.2 and 2.7. Two different long axis lengths are used, namely 25.5 nm and 64 nm. This allows for a
discussion of the size effect for these centrosymmetric nanoparticles. A comparison of the first hyperpolarizabilities
obtained with that of spherical nanoparticles, also centrosymmetric particles, is then made to discuss the role of the shape
of these particles on the origin of the response. For the smallest nanorods, a strong hyperpolarizability normalized per
atom is determined underlining the role of the interface and the shape in determining such a large absolute value. For the
larger nanorods, the first hyperpolarizability per atom is smaller than that of the smaller nanorods but remains larger than
the one obtained for gold nanospheres with a similar volume indicating that the shape and the surface response still
continue to play a major role. These results are in agreement with the multipolar theory for the first hyperpolarizability of
centrosymmetric nanoparticles but show that for nanorods, the surface regime pertains over a longer size range.
The first hyperpolarizability of the aromatic amino acid Tyrosine has been obtained by Hyper Rayleigh Scattering (HRS) in aqueous environment and under non resonant conditions. The rather large value determined is in agreement with previous HRS studies and confirms that Tyrosine can be targeted as an endogenous molecular probe for the second harmonic studies of biological molecules. The same experiment was also performed in an aqueous environment containing 20 nm diameter gold metallic nanoparticles. The resulting first hyperpolarizability measured with the fundamental wavelengths of 815 nm and 1050 nm in these conditions for Tyrosine is reduced as compared to that obtained in absence of metallic nanoparticles.
The Second Harmonic Generation (SHG) response from Tyrosine-containing peptides at the air-water interface is presented. First, the quadratic hyperpolarizability of the aromatic amino acid Tyrosine obtained by Hyper Rayleigh Scattering is reported, demonstrating its potentiality as an endogenous molecular probe for SHG studies. Then, the single Tyrosine antimicrobial peptide Mycosubtilin is monitored at the air-water interface and compared to another peptide, Surfactin, lacking a Tyrosine residue. Adsorption kinetics and polarization analysis of the SHG intensity for the peptide monolayers clearly demonstrate that the SHG response from Mycosubtilin arises from Tyrosine. Besides, it confirms that indeed Tyrosine can be targeted as an endogenous molecular probe.
We describe the multipolar Second Harmonic (SH) response from metallic particles with sizes up to 150 nm. A
particular emphasis is given to the light polarization and size dependence of the SH intensity collected to identify the
different field mechanisms involved and quantify the different sources to the nonlinear polarization. It is shown that the
dipolar, quadrupolar and octupolar modes can be observed depending on the input fundamental and output harmonic
polarization configurations chosen and the size of the particles. We furthermore develop a careful analysis of the
experimental results obtained for the largest size of particles investigated, e.g. 150 nm diameter gold particles, in
conjunction with finite element simulations to compute the different sources to the nonlinear polarization, namely the
surface local and the bulk nonlocal contributions. It is then shown that their relative weight can be determined. These
results are recast within the general model initially proposed by Rudnick and Stern (J. Rudnick and E. A. Stern, Phys.
Rev. B, 4 (1971) 4274).
Second Harmonic Generation was used to study the optical properties of molecular films formed at the air-water
interface. The technique was first applied to a two-dimensional film of 4-(4-dihexadecylaminostyryl)-N-methylpyridinium
iodide (DiA) formed at the air-water interface in a Langmuir trough. The SHG intensity was measured
as a function of the incident fundamental and outgoing harmonic wave polarization angles at different states of the
monolayer compression. The film revealed chirality arising from the formation of molecular aggregates and it was
demonstrated that this chirality property arose from the coupling of the electric and magnetic fields at the fundamental
frequency. In a second stage, we applied the SHG technique to follow the emergence of chirality during the compression
of a molecular film of the amphiphilic compound 5-(octadecyloxy)-2-(2-thiazolylazo) phenol (TARC18). A similar
behavior was observed and it was shown that the same origin was responsible for the appearance of chirality.
Polarization resolved intensity measurements demonstrated that the magnetic dipole contribution was the dominant one.
Single metallic nanoparticle sensitivity in liquid solution was achieved with hyper Rayleigh scattering (HRS). The study
of the HRS intensity fluctuations over time was performed for several dilutions of the nanoparticle solution. Histograms
of the HRS intensity counts were then obtained. These histograms exhibit a Gaussian profile down to low concentrations
before evolving towards Poisson distributions at very low concentrations, demonstrating that the single particle
sensitivity is obtained. Based on these results, we were then able to achieve the three-dimensional mapping of immobile
150 nm gold metallic nanoparticles dispersed in a homogeneous transparent polyacrylamide matrix. Polarization
resolved measurements were also performed allowing for a clear identification of the harmonic light generated by single
gold metallic nanoparticles.
Collagen is characterized by triple helical domains and plays a central role in the formation of fibrillar and
microfibrillar networks, basement membranes, as well as other structures of the connective tissue. Remarkably, fibrillar
collagen exhibits efficient Second Harmonic Generation (SHG) and SHG microscopy proved to be a sensitive tool to
score fibrotic pathologies.
However, the nonlinear optical response of fibrillar collagen is not fully characterized yet and quantitative data are
required to further process SHG images. We therefore performed Hyper-Rayleigh Scattering (HRS) experiments and
measured a second order hyperpolarisability of 1.25 10-27 esu for rat-tail type I collagen. This value is surprisingly large
considering that collagen presents no strong harmonophore in its amino-acid sequence. In order to get insight into the
physical origin of this nonlinear process, we performed HRS measurements after denaturation of the collagen triple
helix and for a collagen-like short model peptide [(Pro-Pro-Gly)10]3. It showed that the collagen large nonlinear response
originates in the tight alignment of a large number of weakly efficient harmonophores, presumably the peptide bonds,
resulting in a coherent amplification of the nonlinear signal along the triple helix. To illustrate this mechanism, we
successfully recorded SHG images in collagen liquid solutions by achieving liquid crystalline ordering of the collagen
triple helices.
We have performed Hyper-Rayleigh Scattering (HRS) experiments to measure the quadratic hyperpolarizability of
several natural amino acids, in particular tryptophan and tyrosine. Values of (29.6+/-0.4)x10-30 esu for tryptophan and
(25.7+/-0.03)x10-30 esu for tyrosine have been found. We have then investigated the dependence of the quadratic
hyperpolarizability of tryptophan-rich short peptides as a function of the number of tryptophans in the sequence. The
experimental findings indicate that the resulting quadratic hyperpolarizability in these peptides cannot be assumed as the
mere coherent superposition of the hyperpolarizabilities of the tryptophans contained in the peptide. Our results
unambiguously demonstrate that there must be strong interactions between the tryptophans contained in these short
peptides. We have also investigated the case of the collagen triple helix. A second order hyperpolarizability of (1.25+/-
0.05)x10-27 esu for rat-tail type I collagen has been measured. In this case, we have been able to model this effective
quadratic hyperpolarizability by summing coherently the nonlinear response of elementary moieties forming the triple
helix, as opposed to the previous case of the tryptophan-rich peptides.
Collagen is a major protein of the extracellular matrix that is characterized by triple helical domains. It plays a
central role in the formation of fibrillar and microfibrillar networks, basement membranes, as well as other structures of
the connective tissue. Remarkably, fibrillar collagen exhibits efficient Second Harmonic Generation (SHG) so that SHG
microscopy proved to be a sensitive tool to probe the
three-dimensional architecture of fibrillar collagen and to assess
the progression of fibrotic pathologies. We obtained sensitive and reproducible measurements of the fibrosis extent, but
we needed quantitative data at the molecular level to further process SHG images. We therefore performed Hyper-
Rayleigh Scattering (HRS) experiments and measured a second order hyperpolarisability of 1.25 10-27 esu for rat-tail
type I collagen. This value is surprisingly large considering that collagen presents no strong harmonophore in its aminoacid
sequence. In order to get insight into the physical origin of this nonlinear process, we performed HRS
measurements after denaturation of the collagen triple helix and for a collagen-like short model peptide [(Pro-Pro-
Gly)10]3. It showed that the collagen large nonlinear response originates in the tight alignment of a large number of
weakly efficient harmonophores, presumably the peptide bonds, resulting in a coherent amplification of the nonlinear
signal along the triple helix. To illustrate this mechanism, we successfully recorded SHG images in collagenous
biomimetic matrices.
The optical second harmonic response from small gold metallic particles with a diameter ranging between 20 and 100 nm is investigated with the technique of Hyper Rayleigh Scattering. The analysis is performed as a function of the polarization state of the incoming fundamental beam. For the particles with the smallest diameters, the nonlinear optical response is purely dipolar, arising from the surface of the particles owing to the breaking of the centrosymmetry of the particles. For larger diameter particles, the retardation effects cannot be neglected anymore, the response exhibiting a clear quadrupolar pattern. A general framework is proposed to discuss the experimental data, based on a a weighing parameter allowing the quanitfication of the relative magnitude of the dipolar and quadrupoloar contributions.
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