The growth kinetics of silver nanoparticles generated by reduction of silver ions (Ag+) in polyvinyl alcohol (PVA) thin films under UV illumination is investigated at various Ag+ initial concentrations. The time evolutions of the UV-visible extinction spectra the Ag nanoparticles were in-situ recorded upon UV illumination. On the basis of transmission electron microscopy images of the nanocomposite film, we show that the time evolutions of the extinction spectra are consistent with the growth of two distinct nanoparticles populations growing in two different phases of the polymer. During the early stage of the process, a rapidly growing nanoparticles population, within the crystallized domain of the polymer, forms closely-packed assemblies of nanoparticles provoking a red-shift of the localized surface plasmon resonance (LSPR) band position due to plasmon coupling. A second population of well-dispersed nanoparticles, growing much more slowly within the amorphous domain of the polymer, comes to gradually dominate the overall optical response of the nanocomposite film causing a blue-shift of the LSPR band position at longer UV illumination time. The validity of the above scenario is supported by a modified Avrami model which takes into account these two concomitant growth processes. These results provide a promising framework for the rational design of plasmonic nanocomposites with tailored optical response by combining optimized polymer microstructure and time-controlled nanoparticles growth.

We study how fermions in molybdenum disulfide MoS2 interact with a laser field and a static potential barrier, focusing on the transmission probability. Our aim is to understand and control photon-assisted quantum transport in this two-dimensional material under external driving. We use the Floquet approximation to describe the wave functions in the three regions of the system. By applying continuity conditions at the boundaries, we obtain a set of equations involving an infinite number of Floquet modes. We explicitly determine transmissions involving the central band E and the first sidebands E +/- `!. As for higher-order bands, we use the transfer matrix approach together with current density to compute the associated transmissions. Our results reveal that the transmission probability oscillates for both spin-up and spin-down electrons. The oscillations of spin-down electrons occur over nearly twice the period of spin-up electrons. Among all bands, the central one consistently shows the highest transmission. We also find that stronger laser fields and wider barriers both lead to reduced transmission. Moreover, laser irradiation enables controllable channeling and filtering of transmission bands by tuning the laser intensity and system parameters. This highlights the potential of laser-driven MoS2 structures for highly sensitive electromagnetic sensors and advanced optoelectronic devices.

We study electron scattering in graphene quantum dots (GQDs) under the combined influence of a magnetic field, an energy gap, and circularly polarized laser irradiation. Using the Floquet approach and the Dirac equation, we derive the energy spectrum solutions. The scattering coefficients are calculated explicitly by matching the eigenspinors at the GQD interfaces, revealing a dependence on several physical parameters. In addition, we compute the scattering efficiency, the electron density distribution, and the lifetime of the quasi-bound states. Our numerical results show that the presence of an energy gap and circularly polarized laser irradiation enhances the localization of the electron density within the GQDs, leading to an increase in the lifetime of the quasi-bound states. In particular, the intensity and polarization of the light influence the scattering process, allowing the manipulation of the electron confinement state. These results highlight the importance of combining magnetic fields and polarized light to control electronic transport in graphene nanostructures.

We investigate MoSSe/AlN heterostructures using first-principles calculations to assess their structural stability, electronic properties, and photocatalytic potential for water splitting. Six stable stacking configurations are identified, all exhibiting indirect band gaps ranging from 0.56 to 1.20 eV (PBE) and 1.03 to 1.73 eV (HSE). Biaxial strain effectively tunes the band gap energies and can induce transitions from indirect to direct band gaps or even metallic states. Applying a perpendicular electric field further modulates the band gap, with bilayer structures showing initial band gap enlargement followed by a sharp decrease, while trilayers generally exhibit a monotonic decrease, leading to potential metallization. Unstrained AA, AB, A ' A ' A ', and AB ' A configurations align favorably with water redox potentials, making them promising for photocatalytic water splitting. Our findings highlight the tunability of MoSSe/AlN heterostructures through stacking, strain, and electric fields, offering insights for designing advanced materials in nanoelectronics and renewable energy applications.

In this study, we explore the optical and thermochromic properties of monoclinic vanadium dioxide (VO2) nanostructures, which undergo a reversible phase transition from an insulating to a metallic state at around 68 degrees C. This phase transition is crucial for applications such as photonic devices, tunable optical filters, and energy-efficient windows. While the performance of VO2 can be optimized by tailoring its nanostructure and film morphology, to the best of our knowledge, no prior work in the literature has successfully synthesized VO2 nanostructures with well-defined morphology and high VO2 purity using the Glancing Angle Deposition (GLAD) technique. In this work, by combining reactive magnetron sputtering of a vanadium target in an Argon-Oxygen atmosphere with GLancing Angle Deposition (GLAD), we synthesized thin films of VO2, followed by post deposition annealing in an oxygen-rich environment. Through GLAD we elaborate anisotropic nanostructures, including tilted and straight columns morphologies. Optical characterizations techniques, such as ellipsometric measurements and grazing incidence X-ray diffraction (GIXRD), were employed to evaluate the crystalline phase and dielectric functions of the films in both their metallic and insulating states. For the tilted nanocolumns, azimuthal Mueller matrix measurements reveal pronounced anisotropic effects. Optical transmission studies show that nanostructured films, particularly those with pillar morphologies, display superior thermochromic performance, with increased transmission, enhanced infrared modulation, and broader hysteresis compared to dense films. The influence of nanostructure porosity on the optical response is also confirmed through simulations using both COMSOL and the Berreman matrix methods, which demonstrate strong agreement in reflectivity predictions. Our work represents a significant advancement in the synthesis of well-defined VO2 nanostructures, opening new pathways for optimizing the material properties for advanced optical and thermochromic applications.

For the first time, we unveil an innovative, one-step approach for synthesizing magnesium nanoparticles (MgNPs), combining efficiency, simplicity, and environmental sustainability. Our method utilizes spin-coating of a magnesium precursor-loaded poly(methyl methacrylate) (PMMA) dispersion onto n-doped silicon substrates. This process induces vapor-driven phase separation, leading to the self-assembly of PMMA into a nanoporous film that encapsulates MgNPs within its nanoholes. Unlike traditional methods that depend on toxic reducing agents or complex synthesis routes, our approach eliminates the need for additional stabilizers, making it a greener and more efficient alternative for nanostructure fabrication. By systematically optimizing precursor concentration and spin-coating speed, we precisely control the size and dispersity of MgNPs, achieving spherical nanoparticles of approximately 50 nm - the smallest size reported to date. Optical characterization using microextinction spectroscopy confirms the presence of localized surface plasmon resonance (LSPR) in the Mg/PMMA composite, demonstrating its potential for advanced sensing applications. X-ray photoelectron spectroscopy (XPS) reveals that MgNPs are passivated by a native MgO layer, enhancing stability and minimizing oxidation under ambient conditions. These substrates exhibit outstanding surface-enhanced Raman scattering (SERS) sensitivity, detecting 4,4 '-bipyridine (4,4 '-BP) at low concentrations. This innovative strategy offers a sustainable path for developing earth abundant plasmonic nanomaterials with tunable optical properties.

Imaging ellipsometry is an optical characterization tool that is widely used to investigate the spatial variations of the opto-geometrical properties of thin films. As ellipsometry is an indirect method, an ellipsometric map analysis requires a modeling step. Classical methods such as the Levenberg-Marquardt algorithm (LM) are generally too time consuming to be applied on a large data set. In this way, an artificial neural network (ANN) approach was introduced for the analysis of an ellipsometric map. As a proof of concept this method was applied for the characterization of silver nanoparticles embedded in a poly -(vinyl alcohol) film. We demonstrate that the LM and ANN give similar results. However, the time required for the ellipsometric map analysis decreases from 15 days for the LM to 1 s for the ANN. This suggests that the ANN is a powerful tool for fast spectroscopic-ellipsometric-imaging analysis. (c) 2024 Optica Publishing Group

The thermal growth of silver nanoparticles (Ag NPs) embedded in polyvinyl alcohol thin films is studied as a function of annealing time by in situ spectroscopic ellipsometry in the visible spectral range. Each recorded spectrum is analyzed by the shape distributed effective medium theory model from which are determined the time evolutions of the film thickness, the shape distribution, the volume fraction of the nanoparticles, and the effective dielectric function of the nanocomposite film. The estimated shape distribution shows that the nanoparticles remain almost spherical in the course of the annealing process in good agreement with the electronic microscopy examinations of the samples. As expected, the films exhibit a plasmon resonance band, the amplitude of which increases during the annealing while the film thickness decreases. The growth mechanism of the silver NPs was also investigated by analyzing the variation of their volume fraction in the films. The obtained results show that the NP growth occurs via a mechanism involving Ag atoms (monomers) additions and/or reduction of Ag ions directly onto the AgNP surface.

Plasmonic anisotropic nanocomposites containing in particular nanorods and nanowires are gaining increasing interest due to their remarkable physical and optical properties. In this paper, we introduce a novel effective medium theory which we call “Orientation and Shape Distributions Effective Medium Theory” (OSDEMT), to describe the optical properties of a 3D arrangement of metallic nanorods in a dielectric matrix. The effective dielectric properties of plasmonic nanocomposites containing nanorods with different shape and orientation configurations were simulated and analyzed using OSDEMT. We demonstrate that the amplitudes of the longitudinal and transverse surface plasmonic resonances depend on the orientation distribution of the nanostructures, when their positions remain unchanged. Moreover, we show that the anisotropic properties of the nanocomposites are very sensitive to the aspect ratios of the nanorods so that even spherical-centered shape distributions exhibit anisotropic properties when oriented. Finally, we confront the OSDEMT to UV-visible extinction measurements conducted on gold nanorods in a toluene suspension.

I. IntroductionOn July 14th, 2015, the New Horizons spacecraft flew by Pluto and revealed the presence of aerosols in the atmosphere [1,2,3] and a curiously dark reddish equatorial region named Cthulhu [1,4]. These photochemical aerosols, extending at more than 350 km of altitude [2,3,5], may affect Pluto atmospheric chemistry and climate [6,7]. Furthermore, it was suggested that these aerosols sediment to constitute the non-icy dark material on the surface of Pluto [4,8]. To interpret the data provided by New Horizons, the atmospheric (e.g. [7]) and surface models (e.g. [4,9]) have so far used the optical constants determined for Titan tholins. Nevertheless, since optical constants strongly depend on the chemical composition of the materials [10], and as Pluto tholins differ chemically from those of Titan [11], Pluto aerosol analogues were synthesized in laboratory and their optical constants were determined by spectroscopic ellipsometry.II. Experimental setup and analyses protocolSynthesis of Pluto tholins We used the PAMPRE experimental setup [12] (LATMOS, France) to synthesize Pluto tholins as thin films onto silicon wafers. For this study, the gas mixture injected into the reactor was composed of variable proportions of N2 and CH4, with 500 ppm of CO [5,13], to simulate photochemical aerosols formed at different altitudes on Pluto (Table 1). The experiments were conducted at a pressure of 0.9 ± 0.1 mbar and at ambient temperature.Table 1: Types of Pluto tholins analyzed in this studyComposition of the gas mixture Corresponding altitude on Pluto [5] Name of the sample 99.5% N2 : 0.5% CH4 : 500 ppm CO < 350 km PH 99% N2 : 1% CH4 : 500 ppm CO 400 km P400 95% N2 : 5% CH4 : 500 ppm CO 600 km P600 Spectroscopic ellipsometry We used the UVISEL (Horiba Jobin Yvon) spectroscopic ellipsometer to analyze Pluto tholins thin films. Spectroscopic ellipsometry is a technique measuring the changes in the polarization state between incident and reflected light on the sample, as a function of wavelength. DeltaPsi2® software was used to fit the ellipsometric data. More precisely, a modified Tauc-Lorentz dispersion model determined the thicknesses of the thin films, and a wavelength-by-wavelength inversion method was used to retrieve the refractive indices n (Fig. 1) and the absorption coefficients k (Fig. 2), from 270 to 2100 nm.III. Optical constants of Pluto tholins from UV to near-IROur study shows: (1) the refractive indices n of Pluto tholins vary from 1.60 to 1.77, and such n-values can correspond to organic polymers [14]; (2) a strong absorption of UV and Visible radiation by Pluto tholins, due to their N- and O-bearing molecules [15,16,17]; (3) a lower absorption in the near-IR with k-values of a few 10-3; (4) a dependency of n and k indices to the altitude of aerosols formation, with especially higher n- and k-values in the UV-Vis spectral range for Pluto low-altitude aerosols (PH and P400).IV. Discussion and ConclusionDue to higher n-values for the samples PH and P400, compared to the P600 sample, we can suppose that aerosols formed in Pluto's lower atmosphere (≤ 400 km of altitude) will differently scatter the light compared to aerosols formed at higher altitudes (> 400 km of altitude) [18], and thus differently affect the photon flux reaching the lower atmosphere and the surface. The strong absorption below 600 nm is likely due to the presence of N- and O-bearing molecules with lone pair, N- and O-containing polycyclic aromatic compounds and unsaturated molecules with extensive conjugated multiple bonds [14-17]. Since the nitrogen and oxygen content is higher in low-altitude tholins [11], their k indices are higher in the UV-Vis wavelength range. We can thus suppose that in Pluto's atmosphere the aerosols formed at different altitudes will differently absorb the photon flux and differently affect Pluto atmospheric and surface radiative transfer [18].As Pluto tholins are chemically different from Titan’s [11], we propose a new set of optical constants to update Pluto atmospheric and surface models that were hitherto based on the optical constants of Titan tholins.AcknowledgementsWe are grateful to the European Research Council Starting Grant PrimChem for funding this work (grant agreement n° 636829).References[1] Stern S. A. et al., Science, Vol. 350, aad1815, 2015.[2] Gladstone G. R. et al., Science, Vol. 351, aad8866, 2016.[3] Cheng A. F. et al., Icarus, Vol. 290, pp. 112-133, 2017.[4] Grundy W. M. et al., Icarus, Vol. 314, pp. 232-245, 2018.[5] Young L. A. et al., Icarus, Vol. 300, pp. 174-199, 2018.[6] Luspay-Kuti A. et al., Monthly Notices of the Royal Astronomical Society, Vol. 472, pp. 104-117, 2017.[7] Zhang X. et al., Nature, Vol. 551, pp. 352-355, 2017.[8] Cruikshank D. P. et al., Icarus, Vol. 246, pp. 82-92, 2015.[9] Protopapa S. et al., Astronomical Journal, Vol. 159, pp. 159-174, 2020.[10] Brassé C. et al., Planetary and Space Science, Vol. 109-110, pp. 159-174, 2015.[11] Jovanović L. et al., Icarus, Vol. 346, 113774, 2020.[12] Szopa C. et al., Planetary and Space Science, Vol. 54, pp. 394-404, 2006.[13] Lellouch E. et al., Icarus, Vol. 286, pp. 289-307, 2017.[14] van Krevelen D. W. and te Nijenhuis K.: Chapter 10: Optical Properties, in Properties of Polymers, pp. 287-320, 2009.[15] Rao C. N. R.: Ultraviolet and visible spectroscopy, 1975.[16] Imanaka H. et al., Icarus, Vol. 168, pp. 344-366, 2004.[17] Lambe A. T. et al., Environmental Science & Technology, Vol. 47, pp. 6349-6357, 2013.[18] Boucher O.: Atmospheric aerosols – Properties and climate impacts, 2015.

We investigate the productivity of ultra-small gold nanoparticles generated by pulsed-laser ablation in liquid of a high-speed rotating gold target as functions of laser ablation time and rotation speed of the target in the range 90-3000 rpm. These experiments were performed byin situmonitoring the extinction spectra of the gold colloidal suspension. The time evolution of the gold volume fraction in the colloidal suspension of the target was determined by modeling the extinction spectra using the shape distribution effective medium theory. The time dependence of the ablation rate, deduced from that of the volume fraction, shows an initial exponential decay followed by a steady-state value at longer ablation time. The influence of the laser-induced roughening of the target surface on the time evolution of the ablation rate is clearly demonstrated. The experimental results also reveal the dependence of the time evolution of the ablation rate of the target on its rotation speed. The effect of the liquid flow on the ablation rate of the target is analyzed and discussed.

This work deals with the effect of Sn doping at mole percentages of 1 %, 2 %, 3 % and 4 % on the structural, morphological, and optical properties of Co3O4 thin films. These physical properties were carried out by X-Ray Diffraction (XRD), Raman, Atomic Force Microscopy (AFM), scanning electron microscope (SEM), Ultraviolet-Visible-Near infrared spectroscopy (UV-Vis-NIR) and spectroscopic ellipsometry (SE). Co3O4 thin films were grown on amorphous glass substrates by spray pyrolysis technique. Experimental and modeling rigorous studies using these different techniques particularly SE were achieved in order to determinate the effect of tin doping on physical properties of cobalt oxide thin films. The incorporation of Sn into the Co sites affects drastically the optical transitions values as well as other optical properties such as the dielectric function, the band gap, the refractive index and the extinction coefficient. All doped samples exhibited a relatively higher absorption coefficient compared to the undoped ones, greater than 105 cm−1 over a wide energy range. SE analysis revealed a smaller transition of approximately 0.77 eV considered as fundamental band gap energy that was assigned to a 3d-d type within the Co2+ tetrahedral site.

Two distinct Ag/Au nanocomposites, namely, hetero-oligomers and eccentric core/shells were obtained by one-step polymer self-assembly-based fabrication. The Ag concentration-dependent, facet-specific passivation, and presence or absence of anisotropic facets were the main factors responsible for controlling the structures of the final products. Based on an understanding of the role of Ag+ ions in controlling the shape of anisotropic gold nanoparticles (AuNPs), tailored concentrations of Ag+ were applied to design nanoparticles with desired anisotropic surface facets to allow site-specific Ag coatings on AuNPs. The Ag additives acted as shape-directing agents due to an underpotential deposition (UPD) that was responsible for stabilizing the various surface facets that enclose the AuNPs. The morphology differences between the substrate samples resulted in discrete plasmonic and sensing features. In surface-enhanced Raman spectroscopy (SERS) studies, we showed that the site-selective deposition of Ag on anisotropic gold nanohexagons (AuNHs) delivers more advantages as compared to their hetero-oligomer nanostructured counterparts due to synergistic effects.

In this Letter, we propose a new, to the best of our knowledge, approach to determine the shape distribution of gold (Au) nanorods from real-time extinction spectroscopy measurements. This method is based on the linearization of the shape distribution effective medium theory (SDEMT). The aspect ratio distribution of Au colloids is obtained in a few tens of ms without any a priori information on the distribution. Both bimodal and monomodal shape distributions of nanoparticles can be extracted by analyzing their extinction spectra. The proposed method is applied to monitor the change in the nanoparticle shape during their exposure to ns-laser pulses.

Due to their tunable physical and chemical properties, alloys are of fundamental importance in material science. The determination of stoichiometry is crucial for alloy engineering. Classical characterization tools such as energy-dispersive x-ray spectroscopy (EDX) are time consuming and cannot be performed in an ambient atmosphere. In this context, we introduce a new methodology to determine the stoichiometry of alloys from ellipsometric measurements. This approach, based on the analysis of ellipsometric spectra by an artificial neural network (ANN), is applied to electrum alloys. We demonstrate that the accuracy of this approach is of the same order of magnitude as that of EDX. In addition, the ANN analysis is sufficiently robust that it can be used to characterize rough alloys. Finally, we demonstrate that the exploitation of ellipsometric maps with the ANN is a powerful tool to determine composition gradients in alloys.

Here, we report an innovative facile polymer-templated synthesis of Ag/Au bimetallic nanoparticles (BNPs) on large surface for sensing. By controlling the reaction kinetics, the bimetallic nanoparticles have been successfully prepared with a variety of structures: heterostructures, eccentric core-shells, and physical mixtures of two metals. The amount and initial shape of the Au seeds determined the final architectures of bimetallic nanostructures. The underlying synthesis mechanism of BNPs was regulated by a seed-mediated growth (SMG) on the surface. The newly formed Ag atoms were directed to selectively nucleate and then epitaxially grow on specific facets of cubic/hexagonal Au seeds. Comprehensive results demonstrating an optical response of two metallic/poly (methyl methacrylate) (M+/PMMA) layers on opaque surfaces by micro-extinction measurements were obtained. Sensors based on anisotropic bimetallic substrates were ideal for sensitive 4,4′-bipyridine (4,4’-BP) detection. The polymer surface-induced accumulation of high electric fields on nanoscale sensing volumes of anisotropic core/shell BNPs allowed more analyte molecules to access their high-index facets. This sample possessed a high surface-enhanced Raman scattering (SERS) sensitivity despite only being validated on very small densities of surfaces; thanks to the synergistic effects between the two coupled metals. The present findings suggest that a surfactant-free synthesis can be used as a powerful mean of defining growth strategies based on silicon substrate platforms.

Photochemical aerosols were detected as high as 350 km of altitude in Pluto's atmosphere during the New Horizons fly-by. These aerosols are thought to affect Pluto's climate, by acting as cooling agents, and the colours of Pluto's surface, in particular in the dark regions named Cthulhu and Krun and at the North Pole. Pluto atmospheric and surface models have so far used the optical constants of Titan aerosol analogues (tholins), whereas their chemical composition is known to differ from that of Pluto aerosol analogues. In order to provide a new set of optical constants for Pluto tholins, we synthesized analogues of Pluto's aerosols and determined with spectroscopic ellipsometry their optical constants from 270 to 2100 nm. Three types of samples were produced from N-2:CH4:CO gas mixtures differing in their CH4:N-2 mixing ratio, representative of different altitudes in Pluto's current atmosphere or different seasons or epochs of Pluto. Our analysis shows a strong absorption by Pluto tholins in the UV and visible spectral ranges, with k index of a few 10(-1) at 270 nm, in agreement with N- and O-bearing organic molecules. Pluto tholins are less absorbent in the near-IR than in the UV-Vis wavelength range, with k of a few 10(3) between 600 and 2100 nm. Our comparative study highlights the dependency of n and k indices to the CH4:N-2 mixing ratio. Aerosols formed at different altitudes in Pluto's atmosphere or during different seasons or epochs of Pluto will therefore affect the budget of Pluto radiative transfer differently. The optical constants presented in this study were tested with a Pluto surface model and with a model of light scattering. The surface modelling results highlight the suitability of these optical constants to reproduce Pluto compositional observations in the visible spectral range by MVIC and LEISA. The atmospheric modelling results conclude that Pluto tholins absorb 5 to 10 times less than Titan tholins at 500 nm, and this lower absorption is consistent with Alice observations of Pluto's haze.

This work describes a novel, one-shot strategy to fabricate ultrasensitive SERS sensors based on silver/poly(methyl methacrylate) (PMMA) nanocomposites. Upon spin coating of a dispersion of PMMA and silver precursor on N-doped silicon substrate, closely separated silver nanoparticles were self-assembled into uniform nanospheres. As a result, a thin hydrophobic PMMA layer embedded with Ag nanoparticles (AgNPs) was obtained on the whole silicon substrate. Consequently, a large-scale, reproducible SERS platform was produced through a rapid, simple, low-cost, and high-throughput technology. In addition, reproducible SERS features and high SERS enhancement factors were determined (SEF ~1015). This finding matches the highest SEF reported in literature to date (1014) for silver aggregates. The potential and novelty of this synthesis is that no reducing agent or copolymer was used, nor was any preliminary functionalization of the surface carried out. In addition, the AgNPs were fabricated directly on the substrate’s surface; consequently, there was no need for polymer etching. Then, the synthetic method was successfully applied to prepare opaque SERS platforms. Opaque surfaces are needed in photonic devices because of the absence of secondary back reflection, which makes optical analysis and applications easier.

One of the key issues for SERS-based trace applications is engineering structurally uniform substrates with ultrasensitivity, stability, and good reproducibility. A label-free, cost-effective, and reproducible fabrication strategy of ultrasensitive SERS sensors was reported in this work. Herein, we present recent progress in self-assembly-based synthesis to elaborate precisely shaped and abundant gold nanoparticles in a large area. We demonstrated that shape control is driven by the selective adsorption of a cation (Na+, K+, and H+) on a single facet of gold nanocrystal seeds during the growth process. We studied SERS features as a function of morphology. Importantly, we found a correlation between the shape and experimental SERS enhancement factors. We observed a detection threshold of 10−20 M of bipyridine ethylene (BPE), which matches the lowest value determined in literature for BPE until now. Such novel sensing finding could be very promising for diseases and pathogen detection and opens up an avenue toward predicting which other morphologies could offer improved sensitivity.

In this paper, we explore the ability of extinction spectroscopy to characterize colloidal suspensions of gold nanoparticles (Au NPs). We demonstrate that the Au NPs' size distribution can be deduced by analyzing their extinction spectra using Mie theory. Our procedure, based on the non-negative least square algorithm, takes advantage of the high sensitivity of the plasmon band to the Au NP size. In addition, this procedure does not require any a priori information on the Au NP size distribution. The Au NPs' size distribution of monomodal or bimodal suspensions can be satisfactorily determined from their extinction spectra. Finally, we show that this characterization tool is compatible with in situ measurement and allows following the change in NPs' radii during laser exposure.