Optics and Spectroscopy (v.122, #1)
Nanostructures based on quantum dots for application in promising methods of single- and multiphoton imaging and diagnostics by I. R. Nabiev (1-7).
Molecules recognizing biomarkers of diseases (monoclonal antibodies (monoABs)) are often too large for biomedical applications, and the conditions that are used to bind them with nanolabels lead to disordered orientation of monoABs with respect to the nanoparticle surface. Extremely small nanoprobes, designed via oriented conjugation of quantum dots (QDs) with single-domain antibodies (sdABs) derived from the immunoglobulin of llama and produced in the E. coli culture, have a hydrodynamic diameter less than 12 nm and contain equally oriented sdAB molecules on the surface of each QD. These nanoprobes exhibit excellent specificity and sensitivity in quantitative determination of a small number of cells expressing biomarkers. In addition, the higher diffusion coefficient of sdABs makes it possible to perform immunohistochemical analysis in bulk tissue, inaccessible for conventional monoABs. The necessary conditions for implementing high-quality immunofluorescence diagnostics are a high specificity of labeling and clear differences between the fluorescence of nanoprobes and the autofluorescence of tissues. Multiphoton micros-copy with excitation in the near-IR spectral range, which is remote from the range of tissue autofluorescence excitation, makes it possible to solve this problem and image deep layers in biological tissues. The two-photon absorption cross sections of CdSe/ZnS QDs conjugated with sdABs exceed the corresponding values for organic fluorophores by several orders of magnitude. These nanoprobes provide clear discrimination between the regions of tumor and normal tissues with a ratio of the sdAB fluorescence to the tissue autofluorescence upon two-photon excitation exceeding that in the case of single-photon excitation by a factor of more than 40. The data obtained indicate that the sdAB-QD conjugates used as labels provide the same, or even better, quality as the “gold standard” of immunohistochemical diagnostics. The developed nanoprobes are expected to find wide application in high-efficiency imaging of tumor and multiparameter diagnostics.
Ultrasmall quantum dots for fluorescent bioimaging in vivo and in vitro by P. A. Linkov; K. V. Vokhmintcev; P. S. Samokhvalov; I. R. Nabiev (8-11).
Photoluminescent semiconductor quantum dots (QDs) are widely used in many branches of diagnostics and biomedicine. Using ultrasmall QDs for designing fluorescent nanoprobes increases their capacity for penetrating through cell membranes, which allows one to use them for tracking intracellular processes at the molecular level. Obtaining small-size QDs is usually impeded due to the fast kinetics of reactions of their formation and growth in a colloidal medium. We propose a method of synthesizing defectless CdSe QDs with a diameter of 1.5 nm based on the injection reaction in an organic medium, with superfast termination of the growth of QDs at the early stage of their formation. Separation of QDs by means of gel-permeation chromatography allows one to completely remove the excess of cadmium precursors not entering the reaction, which ensures the subsequent obtaining of QDs with a controllable fluorescence wavelength and high quantum yield in the process of depositing protective epitaxial shells of different compositions. The obtained ultrasmall QDs may find application in developing photoluminescent nanoprobes for visualizing intranuclear processes in cells.
A highly efficient white-light-emitting diode based on a two-component polyfluorene/quantum dot composite by S. V. Dayneko; P. S. Samokhvalov; D. Lypenko; G. I. Nosova; I. A. Berezin; A. V. Yakimanskii; A. A. Chistyakov; I. Nabiev (12-15).
Organic light-emitting diodes (OLEDs) are attracting great interest of the scientific community and industry because they can be grown on flexible substrates using relatively simple and inexpensive technologies (solution processes). However, a problem in the fabrication of white OLEDs is that it is difficult to achieve a balance between the intensities of individual emission components in the blue, green, and red spectral regions. In this work, we try to solve this problem by creating a two-component light-emitting diode based on modified polyfluorene (PF-BT), which efficiently emits in the blue–green region, and CdSe/ZnS/CdS/ZnS semiconductor quantum dots emitting in the orange–red region with a fluorescence quantum yield exceeding 90%. By changing the mass ratio of components in the active light-emitting composite within 40–50%, it is possible to transform the diode emission spectrum from cold to warm white light without loss of the diode efficiency. It is very likely that optimization of the morphology of multilayer light-emitting diodes will lead to further improvement of their characteristics.
Optical properties of structures composed of periodic, quasi-periodic, and aperiodic sequences of particulate monolayers by V. A. Loiko; A. A. Miskevich (16-24).
The spectra of the coherent transmission and reflection coefficients of multilayers consisting of the periodic, Fibonacci (quasi-periodic), and Thue–Morse (aperiodic) sequences of plane-parallel monolayers of monodisperse spherical alumina and silica particles are investigated using the quasi-crystalline approximation (QCA) and the transfer matrix method (TMM). The additional opportunities for the transmission and reflection spectra manipulation in comparison with the periodic sequence of monolayers are demonstrated. Photonic band gaps in the spectra of the particulate structures are shifted to the short-wavelength range in comparison with those for systems of homogeneous layers. The shift is larger for the Thue–Morse sequence. The widths of the photonic band gaps for particulate systems are narrower than the ones for multilayers consisting of homogeneous layers of an equivalent volume of matter. The results can be used to create optical, optoelectronics, and photonics devices—for example, multispectral filters, light emitting diodes, solar cells, displays.
The influence of ligand type on self-organization and optical properties of cadmium selenide quantum dots by E. V. Ushakova; T. K. Kormilina; M. A. Burkova; S. A. Cherevkov; V. V. Zakharov; V. K. Turkov; A. V. Fedorov; A. V. Baranov (25-29).
A method for successive replacement of organic shells of colloidal cadmium selenide quantum dots (QDs) of different sizes is proposed. It is found that the spectral parameters of QD samples depend on the type of organic shells. It is shown that the structural morphology is independent of the QD size and is determined by the chemical composition of the organic shell. Spectral analysis of the luminescence of QD-based superstructures shows that the luminescence wavelength and intensity strongly depend on the degree of QD surface passivation.
The effect of plasmon silver and exiton semiconductor nanoparticles on the bacteriorhodopsin photocycle in Halobacterium salinarum membranes by V. A. Oleinikov; E. P. Lukashev; S. Yu. Zaitsev; A. A. Chistyakov; D. O. Solovyeva; K. E. Mochalov; I. Nabiev (30-35).
The interaction of semiconductor quantum dots and silver nanoparticles (AgNPs) with bacteriorhodopsin (BR), a membrane protein contained in the purple membrane (PM) of Halobacterium salinarum, is studied. It is shown that both types of nanoparticles are adsorbed efficiently on the surface of the purple membranes, modulating the parameters of the bacteriorhodopsin photocycle. Electrostatic interactions are found to be the main cause of the effect of nanoparticles on the bacteriorhodopsin photocycle. These results explain our earlier data on the “fixation” of the bacteriorhodopsin photocycle for protein molecules trapped after incubation of the purple membranes with silver nanoparticles near the location of the “hot spots” of the effect of surface-enhanced Raman scattering (SERS). It is demonstrated that exposure of silver nanoparticles with bacteriorhodopsin in SERS-active regions lowers the amount of bacteriorhodopsin molecules involved in phototransformations.
Resonant transfer of one- and two-photon excitations in quantum dot–bacteriorhodopsin complexes by V. A. Krivenkov; P. S. Samokhvalov; R. S. Bilan; A. A. Chistyakov; I. R. Nabiev (36-41).
Light-sensitive protein bacteriorhodopsin (BR), which is capable of electrical response upon exposure to light, is a promising material for photovoltaics and optoelectronics. However, the rather narrow absorption spectrum of BR does not allow achieving efficient conversion of the light energy in the blue and infrared spectral regions. This paper summarizes the results of studies showing the possibility of extending the spectral region of the BR function by means of the Förster resonance energy transfer (FRET) from CdSe/ZnS quantum dots (QDs), which have a broad spectrum of one-photon absorption and a large twophoton absorption cross section (TPACS), to BR upon one- and two-photon excitation. In particular, it is shown that, on the basis of QDs and BR-containing purple membranes, it is possible to create electrostatically associated bio-nano hybrid systems in which FRET is implemented. In addition, the large TPACS of QDs, which is two orders of magnitude larger than those of BR and organic dyes, opens up a means for selective two-photon excitation of synthesized bio-nano hybrid complexes. On the basis of the results of this work, the spectral region in which BR converts the light energy into electrical energy can be extended from the UV to near-IR region, creating new opportunities for the use of this material in photovoltaics and optoelectronics.
Optical activity of helical quantum-dot supercrystals by A. S. Baimuratov; N. V. Tepliakov; Yu. K. Gun’ko; A. V. Baranov; A. V. Federov; I. D. Rukhlenko (42-47).
The size of chiral nanoparticles is much smaller than the optical wavelength. As a result, the difference in interaction of enantiomers with circularly polarized light of different handedness is practically unobservable. Due to the large mismatch in scale, the problem of enhancement of enantioselectivity of optical properties of nanoparticles is particularly important for modern photonics. In this work, we show that ordering of achiral nanoparticles into a chiral supercrystal with dimensions comparable to the wavelength of light allows achieving nearly total dissymmetry of optical absorption and demonstrate this using a helical super-crystal made of semiconductor quantum dots as an example. The proposed approach may find numerous applications in various optical and analytical methods used in biomedicine, chemistry, and pharmacology.
Synthesis of quantum dot nanocrystals and plasmonic nanoparticles using a segmented flow reactor by R. C. Mbwahnche; L. B. Matyushkin; O. A. Ryzhov; O. A. Aleksandrova; V. A. Moshnikov (48-51).
The purpose of this research is to develop an automated method of synthesizing quantum dot nanocrystals and plasmonic nanoparticles using segmented flow rector synthesis as a new alternative to the batch method of synthesizing nanoparticles. A reactor was successfully applied to the synthesis of colloidal solutions of semiconductor (CdSe) and metal (Ag) nanoparticles. This instrument is applicable in both material science laboratories and industry.
Plasmonic particles of colloidal silver in high-resolution recording media by O. V. Andreeva; N. V. Andreeva; T. B. Kuzmina (52-58).
The optical properties of colloidal silver particles formed photographically in high-resolution silver halide photographic materials have been considered. The conditions that allow one to obtain exposed and developed light-sensitive silver halide particles in the form of colloidal particles of metallic silver having the properties of localized plasmons have been described. The results of the studies of the developed silver particles in traditional photographic materials for image holography and in nanoporous silver halide photographic materials for volume holography have been presented. The perspectives of using plasmonic silver nanoparticles produced photographically have been discussed.
Plasmonic sensors for identification of inorganic microcrystals by E. V. Shabunya-Klyachkovskaya; E. V. Korza; L. L. Trotsiuk; A. S. Matsukovich; O. S. Kulakovich (59-63).
A method of applying giant stimulated electronic Raman scattering (SERS) by plasmonic gold nanoparticles for identification of inorganic microcrystals in the structure of works of art is presented. The high signal-to-noise ratio in the SERS spectra, along with the low luminescent background, makes the method promising for implementation in practice of technical expertise of objects of cultural heritage.
Optical activity of semiconductor nanocrystals with ionic impurities by N. V. Tepliakov; A. S. Baimuratov; Yu. K. Gun’ko; A. V. Baranov; A. V. Fedorov; I. D. Rukhlenko (64-68).
The strength of the enantioselective interaction of chiral semiconductor nanocrystals with circularly polarized light can be varied over a wide range, which finds a series of important applications in modern nanophotonics. As a rule, this interaction is relatively weak, because the dimension of nanocrystals is much smaller than the wavelength of the optical radiation, and the optical activity of nanocrystals is rather low. In this work, we show theoretically that, by applying ion doping, one can significantly enhance the optical activity of nanocrystals and to vary its magnitude over a wide range of values and over a wide range of frequencies. We show that, by precisely arranging impurities inside nanocrystals, one can optimize the rotatory strengths of intraband transitions, making them 100 times stronger than typical rotatory strengths of small chiral molecules.
The influence of the quantum dot/polymethylmethacrylate composite preparation method on the stability of its optical properties under laser radiation by M. A. Zvaigzne; I. L. Martynov; V. A. Krivenkov; P. S. Samokhvalov; I. R. Nabiev (69-73).
Photoluminescent semiconductor nanocrystals, quantum dots (QDs), are nowadays one of the most promising materials for developing a new generation of fluorescent labels, new types of light-emitting devices and displays, flexible electronic components, and solar panels. In many areas the use of QDs is associated with an intense optical excitation, which, in the case of a prolonged exposure, often leads to changes in their optical characteristics. In the present work we examined how the method of preparation of quantum dot/polymethylmethacrylate (QD/PMMA) composite influenced the stability of the optical properties of QD inside the polymer matrix under irradiation by different laser harmonics in the UV (355 nm) and visible (532 nm) spectral regions. The composites were synthesized by spin-coating and radical polymerization methods. Experiments with the samples obtained by spin-coating showed that the properties of the QD/PMMA films remain almost constant at values of the radiation dose below ~10 fJ per particle. Irradiating the composites prepared by the radical polymerization method, we observed a monotonic increase in the luminescence quantum yield (QY) accompanied by an increase in the luminescence decay time regardless of the wavelength of the incident radiation. We assume that the observed difference in the optical properties of the samples under exposure to laser radiation is associated with the processes occurring during radical polymerization, in particular, with charge transfer from the radical particles inside QDs. The results of this study are important for understanding photophysical properties of composites on the basis of QDs, as well as for selection of the type of polymer and the composite synthesis method with quantum dots that would allow one to avoid the degradation of their luminescence.
Silicon photonic structures with embedded polymers for novel sensing methods by E. V. Osipov; I. L. Martynov; D. S. Dovzhenko; P. S. Ananev; G. E. Kotkovskii; A. A. Chistyakov (74-78).
At present time research and development of a new generation of optical sensors using conjugated polymers, in particular sensors of explosives are actively underway. Nevertheless, the problems of the sensitivity, selectivity, and stability of such sensors are still of great interest. One of the ways to solve the problem is the creation of luminescence sensors based on photonic crystals with a high specific surface area, which have significant sorption ability and allow to effective modulate emission properties of luminophores. In this paper, porous silicon microcavities with embeded organic polyphenylenevinylene- (PPV) and polyfluorene- (PF) type polymers were created. It was shown that polymer infiltration in porous silicon microcavities leads to modification of their luminescence properties, which is expressed in narrowing of the emission spectrum and changing of its directional pattern. It was demonstrated that such structures exhibit sensitivity to saturated vapors of trinitrotoluene. The structures proposed can be treated as a basis for development of new type of sensors used for detection of vapors of nitroaromatic compounds.
Modeling of the optical properties of porous silicon photonic crystals in the visible spectral range by D. S. Dovzhenko; I. L. Martynov; I. S. Kryukova; A. A. Chistyakov; I. R. Nabiev (79-82).
Optical devices based on photonic crystals are of great interest because they can be efficiently used in laser physics and biosensing. Photonic crystals allow one to control the propagation of electromagnetic waves and to change the emission characteristics of luminophores embedded into photonic structures. One of the most interesting materials for developing one-dimensional photonic crystals is porous silicon. However, an important problem in application of this material is the control of the refractive index of layers by changing their porosity, as well as the refractive index dispersion. In addition, it is important to have the possibility of modeling the optical properties of structures to choose precisely select the fabrication parameters and produce one-dimensional photonic crystals with prescribed properties. In order to solve these problems, we used a mathematical model based on the transfer matrix method, using the Bruggeman model, and on the dispersion of silicon refractive index. We fabricated microcavities by electrochemical etching of silicon, with parameters determined by the proposed model, and measured their reflection spectra. The calculated results showed good agreement with experimental data. The model proposed allowed us to achieve a microcavity Q-factor of 160 in the visible region.
The effect of an external electric field on photoluminescence of CdSe colloidal nanoparticles of different topologies by A. O. Muravitskaya; L. I. Gurinovich; A. V. Prudnikau; M. V. Artemyev; S. V. Gaponenko (83-87).
Photoluminescence of CdSe colloidal nanocrystals of different topologies in an external electric field has been studied. It has been found that quenching of photoluminescence, which takes place in quantum dots, is proportional to the square of the field, and in elongated nanocrystals quenching of photoluminescence is proportional to the square root. A physical model of the mechanism of quenching based on tunneling of free charges through potential barrier nanocrystal/matrix has been proposed.
Energy transfer in rigid solutions with nonuniform distribution of components based on quantum dots and organic molecules by Yu. A. Gromova; M. A. Kurochkina; V. G. Maslov; A. V. Baranov; A. V. Fedorov; A. O. Orlova (88-92).
Energy transfer in hybrid structures based on colloidal quantum dots of CdSe/ZnS and molecules of tetra(p-trimethylamino)phenylporphin formed in polyethylene terephthalate track membranes is considered. A physical model for the formation of these hybrid structures is proposed, and the distribution of structure components in the near-surface layer of track membrane pores is estimated.
Obtaining of images of ordered and disordered nanocrystal structures by atomic force microscopy by P. S. Parfenov; A. P. Litvin; E. V. Ushakova; A. V. Fedorov; A. V. Baranov (93-95).
The morphology of films, superlattices, and other structures of colloidal nanocrystals has been investigated by atomic force microscopy (AFM). The capabilities of ultrasharp and conventional probes for AFM are compared. The problems of detection of nanocrystal close packing are discussed.
Circular dichroism spectroscopy of chlorin e6 and its complexes with quantum dots in different media by E. V. Kundelev; A. O. Orlova; V. G. Maslov; A. V. Baranov; A. V. Fedorov (96-100).
The circular dichroism (CD) spectra of chlorin e6 and its complexes with ZnS:Mn/ZnS and CdSe/ZnS quantum dots (QDs) in aqueous solutions with different pH, in methanol, and in dimethyl sulfoxide (DMSO) have been experimentally investigated. The changes in the CD spectra of free chlorin e6 caused by its complexing with semiconductor QDs are analyzed. The application of CD spectroscopy made it possible to record for the first time the CD spectrum of luminescent dimer of chlorin e6 and reveal a nonluminescent aggregate of chlorin e6 (interpreted preliminary as a “tetramer”), the anisotropy factor of which exceeds that of its monomer by a factor of 40. An analysis of the experimental data shows that chlorin e6 in a complex with QDs can be either in the monomeric form or in the form of a nonluminescent “tetramer.” The interaction with a relatively low-stable luminescent dimer of chlorin e6 with QDs leads to its partial monomerization and formation of complexes where chlorin e6 is in the monomeric form.
Absorption properties of one- and two-dimensional semiconductor nanocrystals in the presence of an electric field by N. V. Tepliakov; M. Yu. Leonov; A. V. Baranov; A. V. Fedorov; I. D. Rukhlenko (101-105).
We have considered the broadening of optical absorption spectra of ensembles of randomly oriented nanorods and nanoplatelets that is caused by the action of a static electric field. It has been found that the linewidth in the spectra of the considered nanocrystals depends nonlinearly on the field strength and attains saturation in fields on the order of 100 kV/cm. We show that, due to a weak confinement, the electrooptical response of nanoplatelets is stronger than that of nanorods, which leads to a number of distinctive features in the field-induced broadening of the spectra of nanoplatelets and gives grounds to state that nanoplatelets are the most promising objects for use in electrooptical devices.
Photoinduced processes in hybrid structures on the basis of ТіO2 nanoparticles and CdSe/ZnS quantum dots by E. P. Kolesova; A. O. Orlova; V. G. Maslov; Yu. K. Gun’ko; O. Cleary; A. V. Baranov; A. V. Fedorov (106-109).
The morphology of and photoinduced changes in the luminescent properties of hybrid structures on the basis of TiO2 nanoparticles and CdSe/ZnS quantum dots are studied. It is established that the morphology of the structures depends on the method of their formation and the type of stabilizer of the CdSe/ZnS surface. It is shown that a photoinduced decrease in the efficiency of nonradiative relaxation of the excitation in the quantum dots leads to an increase in the quantum yield of their luminescence and an increase in the efficiency of photoinduced charge transfer in hybrid structures.
Synthesis and characterization of colloidal nanocrystals of ternary chalcogenide compounds by D. S. Mazing; A. I. Shul’ga; L. B. Matyushkin; O. A. Aleksandrova; V. A. Moshnikov (110-113).
Colloidal nanocrystals of CuInS2 and CuInSe2 were synthesized in an apolar noncoordinating medium using 1-dodecanethiol as a ligand. A semiconductor shell of ZnS was formed for CuInS2 nanocrystals obtained by the injection method. The obtained samples were characterized by absorption spectroscopy and photoluminescence.
Hybrid structures based on quantum dots and graphene nanobelts by I. A. Reznik; Yu. A. Gromova; A. S. Zlatov; M. A. Baranov; A. O. Orlova; S. A. Moshkalev; V. G. Maslov; A. V. Baranov; A. V. Fedorov (114-119).
Luminescence and photoelectric properties of hybrid structures based on CdSe/ZnS quantum dots (QDs) and multilayer graphene have been investigated. A correlation between the luminescence quantum yield of QDs and their photoelectric properties in hybrid structures is established. It is shown that a decrease in the QD luminescence quantum yield due to adsorption of 1-(2-pyridylazo)-2-naphtol azo dye molecules onto the QD surface and a photoinduced increase in the QD luminescence quantum yield are accompanied by a symbate change in the hybrid structure photoconductivity.
Quasi-classical description of the stark effect for an electron in an image-potential state by P. A. Golovinskii; M. A. Preobrazhenskii (120-127).
The quasi-classical approximation is used for establishing the positions of the classical turning points of an electron in an image-potential state exposed to an electric field of arbitrary strength perpendicular to the metal surface. It is demonstrated that the behavior of the system in electric fields of different directions is fundamentally different, which makes the dynamics of the low-dimensional system qualitatively different from that of its three-dimensional analog. The electric field strength leading to transition from the tunnel ionization regime to the regime of above-barrier decomposition is determined. The wavefunction of the bound electron state, which explicitly takes into account the influence of the electric field, is expressed in terms of elliptic integrals. The quantization condition is formulated, and the linear and quadratic in the field corrections to the electron energy are found. It is demonstrated that the difference between the linear Stark effect calculated by means of the perturbation theory and the quasi-classical energy shift in a weak field rapidly decreases with increasing quantum level number.
Formation of new Tm3+ tetragonal symmetry optical centers in CaF2 hot-formed laser ceramics by M. E. Doroshenko; O. K. Alimov; A. G. Papashvili; K. A. Martynova; V. A. Konyushkin; A. N. Nakladov; V. V. Osiko (128-132).
By means of time-resolved site-selective spectroscopy the formation of new Tm3+ optical centers with modified local environment and presumably tetragonal local symmetry in CaF2 hot-formed laser quality ceramics is observed. The spectroscopic properties of these new Tm3+ optical centers are investigated and shown to differ strongly from that for regular tetragonal optical centers.
Spectral-luminescent properties of silver molecular clusters and nanoparticles formed by ion exchange in antimony-doped photo-thermo-refractive glasses by E. M. Sgibnev; N. V. Nikonorov; A. I. Ignat’ev (133-138).
The formation of silver molecular clusters and nanoparticles in photo-thermo-refractive (PTR) glasses with different antimony contents has been investigated using ion exchange with subsequent thermal treatment. The influence of the antimony oxide (Sb2O3) concentration and treatment temperature on the spectral-luminescent properties of silver molecular clusters and nanoparticles in glass has been investigated. It is shown that silver molecular clusters in PTR glasses are characterized by strong broadband luminescence in the visible and near-IR ranges and that the formation of silver nanoparticles leads to luminescence quenching.
V.L. Ginzburg’s elliptic screw polarization modes in an optical medium with linear birefringence and twist: Determination of their parameters by the method of Jones matrices by G. B. Malykin; V. I. Pozdnyakova (139-146).
Using the method of Jones matrices, we have calculated parameters of elliptic screw polarization modes (ESPMs). ESPM formalism has been proposed by V.L. Ginzburg for an optical medium with unperturbed linear birefringence and circular birefringence induced by twisting of the medium. The evolution of the polarization state of radiation (PSR) in relation to the length of the examined optical medium has been considered, which is important for twisted single-mode optical fibers and cholesteric liquid crystals. We have shown that the problem can be substantially simplified if the evolution of ESPMs is considered in a screw coordinate system comoving with the twist of the optical medium. In particular, we have shown that a curve on the Poincaré sphere mapping the evolution of the PSR for natural (normal) waves of the examined optical medium in the screw coordinate system degenerates into a point. For comparison, we have found natural waves of this medium in a fixed (laboratory) coordinate system and considered the evolution of their PSR, which is represented by a complex curve on the Poincaré sphere. Also, the evolution of the PSR of improper waves passed through the examined optical medium has been studied in both the fixed and the screw coordinate systems.
Specific features of the circular dichroism of a chiral photonic crystal with a defect layer inside in the presence of a gain by A. H. Gevorgyan (147-154).
The specific features of the circular dichroism (CD) spectra of a cholesteric liquid crystal (CLC) layer with a defect layer inside in the presence of gain have been investigated. The features of the dependence of CD on the parameter characterizing the gain on the defect mode are analyzed for two cases: (i) gain is present in the defect layer and is absent in the CLC sublayers and (ii) gain is absent in the defect layer but is present in the CLC sublayers. It is shown that these dependences significantly differ in the two aforementioned cases. The dependences of the reflection, transmission, and absorption on the defect mode on the gain parameter have been investigated for incident light with both circular polarizations.
Spectroscopy of a laser plume arising under radiation of a ytterbium fiber laser by V. V. Osipov; V. I. Solomonov; A. V. Spirina; V. V. Lisenkov; V. V. Platonov; A. V. Podkin (155-161).
The spectra of luminescence of plumes that occur near targets of Nd: Y2O3, YSZ, and Al2O3 when they are irradiated by pulses of a ytterbium fiber laser with a wavelength of 1.07 μm, duration of 1450 μs, and intensity of 0.4 MW/cm2 are studied. Craters with a diameter of 400 μm and a depth of 600 μm appeared under such exposure in the targets. It is shown that the bands of the cation’s radicals of the targets, the intensities of which are distributed according to a law close to Planck’s law, predominate in the spectra of the plumes. On this basis, the temperature of the plumes was determined. It was about 2200–2280 K at the surface of the target, which is below the boiling temperature of the target due to cooling of the vapor during the passage of the deep laser crater.