Spectral Dependence of Selective Photomodification in Fractal Aggregates of Colloidal Particles

Abstract

Localization of optical excitations and selective photomodification are studied experimentally in fractal aggregates of silver colloidal nanoparticles. The localized optical excitations of the fractal colloids cover a broad spectral range, from the visible to the infrared. We show that the absorbed laser energy is localized in an increasingly smaller number of particles with increasing the laser wavelength from 355 to 1900 nm. The size of the photomodified regions can be as small as 20 nm. The observed modification is explained by optically induced sintering (coalescence) of colloidal nanoparticles. [S0031-9007(97)05209-5]

Direct observation of localized dipolar excitations on rough nanostructured surfaces

“…This feature should be definitely investigated further as it might be important for practical applications associated, for example, with persistent holes induced by laser radiation in the spectra of fractals. 23,44 …”

“…[15][16][17] However, in metal fractal nanocomposites the localization tends to increase, on average, when the wavelength changes from the plasmon resonance of an isolated metal spherule (ϳ400 nm) to the infrared, as was confirmed both theoretically 9,[19][20][21] and experimentally. 22,23 Apart from the fact that, despite the chaotic behavior, the average localization length of dipolar eigenmodes tends to decrease with the wavelength, it should be noted that even if an eigenmode is delocalized ͑its gyration radius is of the order of the sample size͒, it can consist of several relatively small regions of high intensity which are spatially separated and, experimentally, viewed as ''hot spots.'' Direct experimental evidence of the existence of localized dipolar excitations in fractal structures is still scarce.…”

Light Control of Fractal Nanoparticles

“…The publications (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) and conference presentations (a-1) listed in Section III describe work done at le^t partially in support of this grant. During the grant, several types of theoretical and experimental investigations were performed with the unifying goal of understanding and quantifying the enormous enhancement of nonlinear optical responses in fractal aggregate and fractal/microcavity composite media.…”

“…Recent research h^ focused on the development of passive optical control devices [1]. Passive systems may be very simple and very f^t; however, they place great emphasis on the nonlinear optical properties of the media used to fabricate the control device.…”

Plasmonic Nanoparticle Aggregates in High-Intensity Laser Fields: Effect of Pulse Duration

“…In the experiments on laser-induced photochromic processes in Ag nanocolloids occurring near the laser radiation frequency, we observed the effect of spectral-and polarizationselective transparency with formation of a spectrally selective dip [11][12][13] in the inhomogeneously broadened plasmon absorption spectrum of the Ag nanoparticle aggregate [14]. Moreover, the spectral dips formed by picosecond and nanosecond pulses had a different sign of shift relative to the laser wavelength [12].…”