Thermal effects in systems of colloidal plasmonic nanoparticles in high-intensity pulsed laser fields [Invited] (original) (raw)
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Optical Materials Express, 2017
We have studied light induced processes in nanocolloids and composite materials containing ordered and disordered aggregates of plasmonic nanoparticles accompanied by their strong heating. A universal comprehensive physical model that combines mechanical, electrodynamical, and thermal interactions at nanoscale has been developed as a tool for investigations. This model was used to gain deep insight on phenomena that take place in nanoparticle aggregates under high-intensity pulsed laser radiation resulting in the suppression of nanoparticle resonant properties. Verification of the model was carried out with single colloidal Au and Ag nanoparticles and their aggregates.
Chinese Physics B, 2016
We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles (resonant domains) in large colloidal nanoparticle aggregates having different interparticle gaps and particle size distributions. These processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle aggregates. To describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action, we introduce the factor of spectral photomodification. Based on calculation of changes in thermodynamic, mechanical, and optical characteristics of the domains, the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps, an average particle size, and the degree of polydispersity. Variations in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of domains. The obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.
Applied Physics B, 2009
The specific optical nonlinearities inherent in aggregates of metal nanoparticles under pico-and nanosecond pulsed laser irradiation are studied in nanoparticle aggregates formed in silver hydrosols. The results of experimental studies of the correlation between the degree of aggregation of silver hydrosols and their nonlinear refraction index (n2) at the wavelengths 0.532 and 1.064 µm are discussed. The experiments revealed that n2 changes its sign at 1.064 µm as the degree of the hydrosol aggregation grows. The role of various processes occurring in resonant domains of aggregates and the kinetics of these processes under laser irradiation resulting in dynamic variation of the polarizability of aggregates are analyzed. The areas under study included the kinetics of particles displacement considering dissipative forces, heating of the particles and of the surrounding medium depending on the wavelength, intensity and duration of laser pulses. A theory of interaction of laser radiation with an elementary type domain-two bound silver nanoparticles-was developed to describe the kinetics of resonant domains photomodification in aggregates. This theory takes into account thermal, elastic, electrostatic and light induced effects. The experimental results on laser photomodification of silver particle aggregates are discussed in the context of our model. These results include photochromic and nonlinear optical effects, in particular, the nonlinear refraction and nonlinear absorption.
Paradoxes in laser heating of plasmonic nanoparticles
New Journal of Physics, 2012
We study the problem of the laser heating of plasmonic nanoparticles and demonstrate that, in sharp contrast to the common belief, a particle with a small dissipative constant absorbs much more energy than the particle with a large value of this constant. Even higher effective absorption may be achieved for core-shell nanoparticles. Our analysis uses the exact Mie solutions, and optimization of the input energy is performed at a fixed fluence with respect to the particle size, wavelength and duration of the laser pulse. We introduce a new quantity, the effective absorption coefficient of a particle, which allows one to compare quantitatively the light absorption by nanoparticles with that of 6 2 a bulk material. We describe a range of parameters where a giant absorption enhancement can be observed and give practical examples of metals whose optical properties vary from weak (potassium) to strong (platinum) dissipation.
Efficient localized heating of silver nanoparticles by low-fluence femtosecond laser pulses
Applied Surface Science, 2015
Highly localized heating can be obtained in plasmonic nanomaterials using laser excitation but the high fluences required often produce unacceptable damage in and near irradiated components and structures. In this work we show that plasmonic nanostructures involving aggregated Ag nanoparticles (Ag NPs) can be heated effectively without attendant damage to the surrounding material when these structures are irradiated with many overlapping femtosecond (fs) laser pulses at very low fluence. Under these conditions, the effectiveness of heating is such that the temperature of 50 nm Ag NPs can be raised to their melting point from room temperature. Aggregates of these NPs are then observed to grow into larger spherical particles as laser heating continues. Imaging of these materials shows that the initiation of melting in individual Ag NPs depends on the local geometry surrounding each NP and on the polarization of the incident laser radiation. Finite difference time domain (FDTD) simulations indicate that melting is triggered by localized surface plasmon (LSP)-induced electric field enhancement at "hotspots".
Interaction of gold nanoparticles with nanosecond laser pulses: Nanoparticle heating
Applied Surface Science, 2011
Theoretical and experimental results on the heating process of gold nanoparticles irradiated by nanosecond laser pulses are presented. The efficiency of particle heating is demonstrated by in-vitro photothermal therapy of human tumor cells. Gold nanoparticles with diameters of 40 and 100 nm are added as colloid in the cell culture and the samples are irradiated by nanosecond pulses at wavelength of 532 nm delivered by Nd:YAG laser system. The results indicate clear cytotoxic effect of application of nanoparticle as more efficient is the case of using particles with diameter of 100 nm. The theoretical analysis of the heating process of nanoparticle interacting with laser radiation is based on the Mie scattering theory, which is used for calculation of the particle absorption coefficient, and two-dimensional heat diffusion model, which describes the particle and the surrounding medium temperature evolution. Using this model the dependence of the achieved maximal temperature in the particles on the applied laser fluence and time evolution of the particle temperature is obtained.
Thermo optical properties of Ag nanoparticles produced by pulsed laser ablation
Optical and Quantum Electronics, 2015
The linear and nonlinear optical properties of silver nanoparticles have been investigated experimentally. Colloidal nanoparticle samples were synthesized by laser ablation at various fluences. The samples were characterized by linear absorption spectroscopy, transmission electron microscopy and dynamic light scattering methods. The behavior of nonlinear refractive index of nanoparticles was studied using the close and open Z-scan techniques by low power CW laser beam. Observation of asymmetrical configurations of the Z-scan curve indicates that nonlinear refraction occurring in the Ag samples is related to the thermo optical process. In addition, the observed optical limiting behavior is due to nonlinear refraction of samples arising from thermal lens formation under low power CW excitation. The optimum position for samples as the optical limiter based on self-defocusing effect is the valley point. When the illumination laser power is low, the self-defocusing effect is mainly dominated. Actually laser fluence variation during the ablation procedure leads to concentration variation of nanoparticles in suspensions which in turn affect the optical properties of samples. The dependence of the nonlinear properties on morphological parameters, metal concentration, and particle size have been explained by experimental results.
Single Laser Pulse Effects on Suspended-Au-Nanoparticle Size Distributions and Morphology
The Journal of Physical Chemistry C, 2013
Samples of suspended gold nanoparticles in the diameter range 10 to 100 nm were subjected to a single 7 ns pulse from a 532 nm laser to determine the effect of laser power on particle size distribution, mean size, and morphology. The experimental techniques used were dynamic light scattering (DLS), depolarized dynamic light scattering (DDLS), electrospray-differential mobility analysis (ES-DMA), ultraviolet−visible absorption spectroscopy, and transmission electron microscopy (TEM). For 60 nm particles, a laser pulse of fluence 10 mJ/cm 2 was sufficient to produce observable changes. In the range 10−72 mJ/cm 2 , DLS indicated little change in mean particle size but a more than three-fold reduction in the polydispersity index (significantly tightened distribution) and a decrease in scattering intensity. TEM showed that the particles became highly spherical and that there was a growing population of particles <10 nm in size that could not be detected by DLS and ES-DMA. Fused dimers were also observed, which suggest that heated particles can interact prior to cooling. DDLS showed a decrease in scattering due to shape anisotropy with a 20 mJ/cm 2 pulse and a decrease in the diffusion time constant. At higher power, the mean particle size decreased until all particles were <10 nm in size. The threshold for observable changes decreased with increasing particle size in the range 10 to 60 nm but increased for 100 nm particles. These results will be useful for potential therapeutic applications for pulse-heated nanoparticles and demonstrate the use of a simple laser treatment for modifying and improving nanoparticle properties.
Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses
The Journal of Physical Chemistry B, 2000
Gold nanorods have been found to change their shape after excitation with intense pulsed laser irradiation. The final irradiation products strongly depend on the energy of the laser pulse as well as on its width. We performed a series of measurements in which the excitation power was varied over the range of the output power of an amplified femtosecond laser system producing pulses of 100 fs duration and a nanosecond optical parametric oscillator (OPO) laser system having a pulse width of 7 ns. The shape transformations of the gold nanorods are followed by two techniques: (1) visible absorption spectroscopy by monitoring the changes in the plasmon absorption bands characteristic for gold nanoparticles; (2) transmission electron microscopy (TEM) in order to analyze the final shape and size distribution. While at high laser fluences (∼1 J cm -2 ) the gold nanoparticles fragment, a melting of the nanorods into spherical nanoparticles (nanodots) is observed when the laser energy is lowered. Upon decreasing the energy of the excitation pulse, only partial melting of the nanorods takes place. Shorter but wider nanorods are observed in the final distribution as well as a higher abundance of particles having odd shapes (bent, twisted, φ-shaped, etc.). The threshold for complete melting of the nanorods with femtosecond laser pulses is about 0.01 J cm -2 . Comparing the results obtained using the two different types of excitation sources (femtosecond vs nanosecond laser), it is found that the energy threshold for a complete melting of the nanorods into nanodots is about 2 orders of magnitude higher when using nanosecond laser pulses than with femtosecond laser pulses. This is explained in terms of the successful competitive cooling process of the nanorods when the nanosecond laser pulses are used. For nanosecond pulse excitation, the absorption of the nanorods decreases during the laser pulse because of the bleaching of the longitudinal plasmon band. In addition, the cooling of the lattice occurring on the 100 ps time scale can effectively compete with the rate of absorption in the case of the nanosecond pulse excitation but not for the femtosecond pulse excitation. When the excitation source is a femtosecond laser pulse, the involved processes (absorption of the photons by the electrons (100 fs), heat transfer between the hot electrons and the lattice (<10 ps), melting (30 ps), and heat loss to the surrounding solvent (>100 ps) are clearly separated in time.