This paper is devoted to the 90th anniversary of the 1924 publication of the seminal paper by Bose titled “Planck’s law and the hypothesis on light quanta” (Zeitschrift für Physik26, 178–181). The paper has been the cornerstone quantum statistical physics. Remarkably, the very starting idea is the discreteness of phase space expressed in the form of the density of states. Bose considered equilibrium electromagnetic radiation as gas of photons and, therefore, introduced the photon density of states notion into the physics though without using directly the term “density of states.” Today, engineering photon density of states to modify light-matter interaction in nanostructures including both spontaneous emission and spontaneous scattering of photons constitutes the solid part of nanophotonics.
A simple chemical technique was devised for the fabrication of silver nanostructured substrates which can be used for plasmonic enhancement of labeled proteins fluorescence. For bovine serum albumin labeled with fluorescein isothiocyanate, the obtained enhancement factor ranges from three to seven, depending on metal-luminophore spacing and silver nanoparticle size. For excitation with linear polarized light, the enhancement factor increases noticeably for p -polarization and decreases for s -polarization. The experimental results were interpreted in terms of the theoretical model in which the enhancement factor depends on incident light polarization, luminophoremetal spacing and silver nanoparticle size. Proposed plasmonic substrates can be considered as an affordable replacement of standard ones in different types of fluorescent assays for the purpose of increasing sensitivity.
Based on analysis of light propagation in multiple cavity aperiodic structures, a filter with three narrow passbands with high transmission is designed. The design is implemented for use in express early-stage oral cancer screening by means of Raman spectroscopy. A combination of SiO2/Nb2O5 is used in a vacuum deposition process to ensure high refractive index contrast and durability of materials. The approach enables the development of simple and affordable Raman testers for multiple medical, forensic, and environmental applications.
Anisotropic optical properties of free nanoporous anodic alumina films transparent in the visible spectrum for the
restricted range of pore diameters and pore intervals are discussed. The basic experimental procedure is presented for the
production of these films. Diagrams of elastic light scattering in two-dimensional nanoporous alumina structures
demonstrated anisotropy due to the spatial distribution of the photon density of states because of the photonic band gap
formation in materials with a periodic change of the refraction index on the scale of the wavelength. A birefringence
value (the difference in the normal and tangential refraction indices) was found from the measurements and computer
modeling to be up to 0.08. Light scattered along pores was experimentally found to have a polarization perpendicular to
the polarization of the incident light. The results obtained show that the nanoporous structure of anodic alumina films can
be purposefully used to control a light propagation, namely, to perform anisotropic light scattering in LCD backlight
systems as well as potential modification of light polarization.
Nonlinear optical properties of GaAs/(AlGa)XOY heterostructures using interband excitation by 150 fs laser pulses is
reported. A considerable wideband nonlinear response is observed. Mean decay time for nonlinear reflection in
heterostructures ranges from 1.5 to 3.5 ps. The shift of the GaAs energy-band structure caused by the high tensions in
GaAs/(AlGa)XOY structure is observed.
Role of incident electromagnetic field enhancement and photon density of states with respect to scattering (Raman and
Rayleigh processes) and spontaneous emission of photons is discussed. Field enhancement and density of states effects
should manifest themselves in the same manner in photoluminescence and scattering processes. Differences in scattering
and luminescence enhancement are due to quenching processes which are less pronounced for scattering but crucial for luminescence because of finite internal relaxation processes between excitation and emission events and. We consider recent experimental results on single molecule detection by means of surface enhanced Raman scattering and photoluminescence enhancement of quantum dots and consider possible approaches to engineering of efficient light emitting nanostructures.
At the early stage of quantum mechanics, classical optical phenomena were used to form intuitive concepts of quantum
interference and diffraction and assisted in development of wave mechanics foundation. Later on, quantum theory of
complex structures has revealed many principal phenomena that have their counterparts in classical electromagnetism.
Progress in nanophotonics is shown to result essentially from systematic transfer of ideas and concepts from quantum
solid state theory to optics. A brief historical overview of the principal nanophotonic concepts and its quantum
counterparts is provided and the possible reasons are discussed why quantum effects have been transferred to
electromagnetism but not vice versa. Based on existing opto-electronic twins, at least 2 cases of non-identified effects are
outlined. These are regularities of electron spectra in fractal heterostructures to be transferred from optics to quantum
physics, and, surface Tamm states to be transferred from quantum physics to nanophotonics.
ZnS/ZnSe heterostructures under condition of ZnSe interband excitation by a 150 fs laser pulse exhibit strong narrow-band
modification of absorption and wide-band modification of reflection. Mean decay time for nonlinear reflection in
heterostructures ranges from 2 to 3 ps whereas in bare ZnSe monolayer it exceeds 5 ps. Possible physical processes
responsible for nonlinear refraction in the transparency region include interplay of absorption driven nonlinear refraction
via Kramers-Kronig relations and intrinsic dielectric properties of dense electron-hole plasma. For nonlinear absorption
at ZnSe band edge, interplay of plasma screening effects and states filling effects are relevant.
ZnS/ZnSe Bragg reflectors under condition of ZnSe interband excitation by a femtosecond laser pulse exhibit strong
narrow-band modification of absorption and wide-band modification of reflection. Mean decay time for nonlinear
reflection in heterostructures ranges from 2 to 3 ps whereas in bare ZnSe monolayer it exceeds 5 ps. Possible underlying
physical processes responsible for nonlinear refraction in the transparency region include interplay of absorption driven
nonlinear refraction via Kramers-Kronig relations and intrinsic dielectric properties of dense electron-hole plasma. For
nonlinear absorption at ZnSe band edge, interplay of plasma screening effects and states filling effects are relevant.
We report on experimental and theoretical investigation of birefringence of free-standing nanoporous anodic alumina
membranes in the optical range. The value of birefringence is analyzed for the samples with different porosities by
measuring polarization dependent transmission spectra at different angles of incidence. The experimental data are
compared to the results of birefringence simulations in accordance with three simulation approaches: modified
Bruggeman effective-medium approximation, Boundary conditions model, plane-wave expansion method. It is both
experimentally and theoretically shown that birefringence value increases with porosity increasing in the low porosity
region. The porous alumina samples under investigation possess greatest value of birefringence (0.062) up to date.
Spectral and localization properties of electromagnetic wave propagation in fractal nanostructures have been reviewed and summarized. Quarter-wave binary multilayer structures have been chosen as a simplest model that would allow to isolate effects pertaining to the geometrical organization of the structure. Intra- and inter-generation scaling relations have been obtained and compared to those known for quasiperiodic structures. Localization patterns have been shown to have an intermediate form between extended and localized eigenstates.
We report on anisotropic light scattering in nanoporous anodic alumina. Light coming at various angles with respect to the pore axis was found to be scattered predominantly in the solid angle adjacent to the pore axis. Such scattering indicatrix we explain in the terms of redistributed local density of photon states in irregular nanostructured materials. In the case of porous alumina local density of photon states and light scattering probability are increased in the direction of the pore axis. We demonstrate by the example of PAA that nanostructured aperiodic materials can possess birefringent
properties. We demonstrate and explain formation of the scattering rings by transmitted laser light in birefringent nanoporous anodic alumina.
Nonlinear optical response of periodic structures based on ZnSe/ZnS heterostructures using interband excitation of a ZnSe sublattice by 1 50 fs laser pulses is reported. A considerable shift of reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. Evaluated refraction index change is about -0.02 with the relaxation time being about 3 picoseconds. The nonlinear refraction is supposed to be controlled by population induced absorption changes in ZnSe single crystals and relevant refraction index modification via Kramers-Kronig relations. The nonlinearity relaxation time is supposed to trace a transition from non-equilibrium to quasi-equilibrium distribution of electrons and holes within ZnSe conduction and valence bands, respectively, rather than electron-hole recombination time. The nonlinearity
mechanism does not reduce to just population dependent absorption saturation but essentially results from the specific distribution function in the first instance after excitation.
A technique is proposed of layer-by-layer laser spectral microanalysis of art pigments, using two-pulse sample atomization with one-shot spectrum registration. The analysis includes on-surface and in-depth profiling of the layer composition. The technique allows to determine distributions of chosen elements along specimen surface. The laser parameters were chosen to obtain regular laser craters of known depth and diameters. The technique has been tested and
optimized at the analysis of model samples with known compositions. The proposed method was used for investigation and ascription two painting from Nesvizh Portrait Gallery (Belarus). The results show good prospects of the LIBS as applied to paintings authentication.
Transmission properties of ultra-short pulses propagating through 1-D photonic crystals (PCs) with multiple cavities were experimentally investigated. Coupling between cavities is responsible for a wide resonance, inside the PC gap, suitable to distortion free propagation of 70 fs pulses at 800 nm. Geometry induced anomalous dispersion across the resonance allows chirp compensation of 70 fs pulses. We use an autocorrelator set-up in order to investigate chirp compensation effect by measuring the time duration of input and output pulses. Measurements are performed for different incidence angle. Results show that complete chirp compensation of 10 fs chirping occurs for an incidence angle of 20 deg.
We investigated ultrafast nonlinear optical properties of periodic structures based on ZnSe/ZnS using interband and two-photon excitation of ZnSe sublatice by nano-, pico-, and femtosecond laser pulses. A considerable shift of reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. The nonlinear refraction is supposed to be controlled by population induced absorption changes in ZnSe and the relaxation time is controlled by a transition from non-equilibrium to quasi-equilibrium distribution of electrons and holes.
We propose to represent complex non-periodic deterministic multilayer nanostructures as numbers in base equal to the number of constituent layer types, e.g., binary numbers for binary multilayers. We have shown that such numbers have correlation with geometrical and spectral properties of nanostructures in question. Possible applications for number identification and information coding are discussed. Numbers corresponding to fractal multilayers (fractal numbers) are shown to possess distinct factorization properties, which can be applied in non-symmetric cryptography. Using multilayers as reverse engineering proof optical keys or embedded identification elements is also considered.
Deposition of coinage metals on a crystallographic surface of a colloidal crystal is proposed with the aim of fabricating metal surfaces with a regular relief on a scale of 200-300 nm to get strong surface enhanced Raman scattering (SERS). The approach is implemented through thin gold-film deposition on a surface of a crystal consisting of silica globules. Mitoxantrone, a DNA intercalator, malachite green and methylene blue molecules were used to prove high Raman and fluorescence enhancement efficiency of the structures proposed. Distance dependence measurements of the mitox secondary emission intensity show a long-range character of enhancement effects. As compared to other SERS-active substrates, metal-dielectric colloidal crystal structures possess well-defined surface parameters (globule diameter and film thickness), high stability and reproducibility. These advantages are important for systematic analysis of SERS mechanisms in mesoscopic structures and its application in single-molecule detection.
Modification of photon density of states (DOS) is considered as an essential factor of modified Raman scattering in mesoscopic media with complicate spatial dependence of dielectric function on a scale of incident/scattered photon wavelengths. Possible contribution of redistributed photon DOS over frequency spectrum in mesoscopic metal-dielectric structures to surface enhancement of Raman scattering (SERS) by adsorbed molecules is outlined. Considerable growth of DOS for a certain mode increase spontaneous scattering rate to this mode which in turn promotes stimulated Raman scattering to the same mode. Therefore total effect of DOS on scattering rate can be higher than DOS increase in a given mesoscopic medium versus vacuum.
Multilayer fractal structures, being a subclass of nonperiodic yet deterministic media are studied in relation to the problem of classical wave propagation. A general case of fractal multilayers is considered. Numerical calculations reveal that the geometry and optical spectra of such structures are directly connected. Namely, it has been found that structures and spectra exhibit exactly the same scaling relations, which are easily derived from the parameters used in the stack construction procedure. Sharp resonant transmission peaks are found to split when the number of generation of the fractal structure increases, and the number of components in such split multiplets is again directly linked to the stack geometrical features. Treating a multilayer structure as a complex coupled-cavity system yields straightforward physical explanations of the properties found. Likeness of fractal properties to occur in the spectra of fractal multilayers is discussed.
Optical properties of fractal Cantor-like multilayer nanostructures are investigated numerically and experimentally. Strong correlation between the stack geometry and the properties of optical transmission spectra is found, namely spectral scalability and sequential splitting. A good agreement is achieved between the experimentally measured and calculated spectra.
Sol-gel process is shown as a promising synthetic route to develop the 3D photonic crystals doped with the optically active terbium. Using silica and Tb-doped titania sols the colloidal crystal with photonic stop band ranging from 480 to 550 nm have been developed, thus fitting the 5D4 yields 7F6 and 5D4 yields 7F5 transition of Tb3+ ions. Pronounced inhibition of optical transitions of Tb3+ ions was observed. The structures fabricated are considered as promising probes to examine the influence of photonic stop band on modification of the spontaneous emission spectra of phosphors.
Mesoscopic structures with characteristic size either of the order of an electron de Broglie wavelength in semiconductors (1 - 10 nm) or close to the optical photon wavelength (100 - 1000 nm) exhibit non-trivial properties due to modified electron or photon density of states. 3D spatial confinement of electrons in nanocrystals (quantum dots) results in size- dependent energies and probabilities of optical transitions. The photon density of states can be modified in structures with strong modulation of the refractive index in three dimensions (photonic crystals) and in microcavities. Because of the essentially different electron and photon wavelengths, electron and photon densities of states can be engineered separately within the same mesostructure. We report here on synthesis and properties of semiconductor quantum dots corresponding to the strong confinement limit embedded either in a photonic crystal exhibiting a pseudogap or in a planar microcavity. We show that the interplay of electron and photon confinement within the same structure opens a way towards novel light sources with controllable spontaneous emission. Spontaneous emission which is not an inherent property of quantum systems but a result of their interaction with electromagnetic vacuum can be either promoted or inhibited depending on the modification of the photon density of states in a given mesostructure.
We show that a promising way towards photonic crystals for the visible range is connected with the synthetic opals which consist of close-packed submicron silica spheres. By filling intersphere voids with different liquids and titanium oxide it is possible to enhance refraction index modulation and to optimize the topology of the structure. Impregnation of opal with absorbing material, such as Fe2O3, allows us to investigate the influence of absorption on the optical properties of the photonic crystals.
The effect of permanent hole burning is studied in absorption spectra of quantum sized CdS nanocrystals with the mean diameter of about 30 angstroms and wide size distribution embedded in polymeric film. The selective photoexcitation of appropriate CdS quantum dots followed by their ionization and further irreversible oxidation of CdS phase by holes h+ is considered to be responsible for this effect.
Population-induced optical nonlinearities and photo-induced spectral hole-burning phenomena in semiconductor nanocrystallites are described. Absorption saturation in small crystallites results in a genuine bleaching in the nanosecond time range with very small non-saturable contribution. In large crystallites exciton-exciton interactions lead to photo-induced blue shift of exciton resonance. Inhomogeneous broadening of absorption spectrum due to size distribution in a quantum dot ensemble results in several hole-burning effects. Along with the transient hole-burning due to absorption saturation the other processes are possible resulting in persistent or irreversible hole burning. The mechanism is proposed of persistent reversible hole-burning based on the local electric field effect due to photoionization or carrier surface localization in the resonantly excited crystallites. Permanent irreversible hole-burning is outlined for which the term `selective photochemistry' is relevant. All phenomena provide a scope of possible applications and at the same time may be used as an effective tool to evaluate intrinsic properties of quantum dots in the inhomogeneously broadened ensembles.
The spectrometer is described designed for studies of the small deviations in inhomogeneously broadened systems under selective laser excitation as well as for time-resolved analysis of irreversible photochemical processes after single-shot excitation. The set-up includes tunable pulse laser and registration system based on CCD-array. Computer control and built-in memory for 256 frames provide sensitivity of about 0.002 optical density units when studying differential absorption spectra and time-resolved single shot spectral measurements in the millisecond range.
Excitonic processes in CuCl nanospheres of mean radius ranging from 2 to 15 nm embedded in a glass matrix are investigated. Specific features resulting from quantum confinement are analyzed. Correlation between nonlinear-optical and photochemical changes have been revealed. The possibility of application of the same structure in the reversible and irreversible optical memory devices is discussed.
For the first time we report spectral hole-burning with the width as small as (Gamma) equals 10 meV for semiconductor quantum dots of the size much smaller than the excitonic Bohr radius of the bulk material. The narrow nonlinear resonances found are typical of the structures prepared at the nucleation and normal growth precipitation stages. The saturation intensity on the order of <EQ 102 kW/cm2 registered for high-quality CdSe-doped glass is close to that for excitonic nonlinearity of CdSe monocrystalline films. The structures grown at the coalescence stage show only broad-band nonlinear absorption with a saturation intensity much higher than the proper bulk material.
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