Search

We record stimulated Raman scattering spectra in chemically-pure glycerol with the formation of two Stokes satellites with equidistant Raman frequencies ν = 2889 cm−1. To excite the scattered radiation, we employ short pulses of the second optical harmonic of a YAG:Nd3+ laser with a wavelength of 532 nm. Using the fundamental harmonic of the YAG:Nd3+ laser λ = 1064 nm, we convert the infrared Stokes component of stimulated Raman scattering into the visible range of the spectrum with the help of a nonlinear crystal of barium titanate. The large Raman shift of the Stokes components of stimulated Raman scattering makes it possible to use glycerol to convert laser radiation into different spectral ranges.

It was found that resonant two-photon-excited luminescence is observed in zinc-phosphate optical glass doped with sodium uranate with a concentration of 2.8%, excited by pulse-periodic radiation of gold vapor laser (λ = 627.8 nm). In this case, the wavelength of exciting laser radiation fell within the absorption band of zinc-phosphate optical glass. The average radiation power of the gold vapor laser was 0.2 W at a lasing pulse repetition rate of 10 kHz and a pulse duration of 15 ns. The peak intensity of focused laser radiation on the sample surface was ~5 × 106 W/cm2. The recorded spectrum of resonant two-photon-excited luminescence consisted of several bands in the green-orange spectral region. The efficiency of resonant two-photon-excited luminescence was about 10–3–10–4, which exceeds the efficiency of two-photon-excited luminescence observed under nonresonant conditions by one—two orders of magnitude.

We report the stimulated Raman scattering of light in synthetic diamond microparticles of close sizes (250–300 μm) with the generation of three Stokes satellites under the excitation by ultrashort (60 ps) YAG:Nd3+ laser pulses at a wavelength of 532 nm. The studies performed open up the possibility of creating a laser frequency array with a frequency shift of 1332 cm–1 based on stimulated Raman scattering of light in synthetic microcrystalline diamond powders in a wide spectral range, including ultraviolet and infrared ranges (0.24–2.50 μm).

Reported are the results of studying the sharp increase in the spectral intensity at the lattice soft mode near the temperature of the phase transition in the lithium tantalate crystal. The Raman scattering spectra are recorded in the x(zz)y polarization geometry corresponding to manifestation of the soft mode responsible for the ferroelectric phase transition in lithium tantalate at 898 K. The recording is performed at fixed temperatures T ( $$I(\omega {\kern 1pt} ',T)$$ , T = const) and at fixed spectrometer frequencies ( $$I(\omega {\kern 1pt} ',T)$$ , $$\omega {\kern 1pt} ' = {{\omega }_{0}} - T = {\text{const}}$$ ) under slow (1 deg./min) crystal temperature variation. Strong increase (by three orders of magnitude) is observed in the peak of the reduced spectral intensity i0(Ω) of the isofrequency temperature dependence at the fixed spectrometer frequency shift relative to the exciting radiation $$\Omega = {{\omega }_{0}} - \omega {\kern 1pt} ' = 10$$ cm–1 similar to the one earlier observed in quartz crystals.

A forward-directed high-efficiency stimulated inelastic light scattering was detected in an aqueous suspension of spherical nanoparticles (nanoballs) of amorphous SiO2 of similar sizes (0.25 μm) with a concentration of 1013 cm-3. In the stimulated scattering spectrum, there was an intense forward directed Stokes component with a frequency shift of 0.54 cm-1, corresponding to the boson peak mode of spherical nanoparticles. The results obtained are of interest for non-equilibrium excitation of spherical particles of similar sizes of different nature present in liquids (clusters, fullerenes, spherical macromolecules, viruses, etc.).

The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering of light in mono- and polydomain lithium tantalate single crystals are established using a backscattering geometry. The relative intensity of the overtone Raman spectrum on the longitudinal and transverse fundamental polar excitations is much higher in the polydomain sample. Unfortunately, the exact reason for the difference in the Raman spectra of the mono- and polydomain lithium tantalate samples is unknown. The frequencies of the two overtone bands exceeded the exact value of the overtone frequency corresponding to the fundamental longitudinal polar mode $4{A}_{1}(\text{LO})$, which clearly indicates the existence of bound phonon pairs (biphonons). This is consistent with theory and has been shown for both mono- and polydomain samples. On the basis of the general theory of bound states of quasiparticles, the possibility of the existence of bound states of quadrupole excitations of the antipolar type in the vibrational spectrum of a polydomain crystal of lithium tantalate is predicted.

Isothermal dependences of Raman scattering intensity i (ω′; T = const) on frequency Ω = ω0 − ω′ and isofrequency temperature dependences of i (Ω = ω0 − ω′ = const; T) in quartz crystals in a wide temperature range, including the α−β phase transition point (ω0 and ω′ are the excitation and Raman frequencies, respectively) have been compared. The isofrequency temperature dependences exhibit an intensity peak (near the phase-transition point), whose spectral position and magnitude depend on the fixed frequency Ω = ω0 − ω′. A theory of these dependences is developed for the crystals undergoing structural phase transitions. The theory predicts a soft-mode effect in the form of Raman opalescence: an anomalous increase in the spectral intensity of the isofrequency maximum i0 (Ω, T) with a decrease in frequency Ω near the phase-transition temperature (T ≈ Tc). Agreement is established between the experimentally observed spectral intensity anomalies and the developed theory of isofrequency temperature dependences and processes of interaction of the fundamental soft mode with a low-frequency high-Q oscillator.

The spectra of multifrequency parametric stimulated Raman scattering in a barium nitrate single crystal is investigated. When this single crystal is excited by ultrashort (80 ps) YAG : Nd3+ laser pulses with a wavelength of 1064 nm, a frequency comb of eight anti-Stokes components is observed in the visible spectral range. The Raman satellites are due to the totally symmetric vibrational modes of barium nitrate single crystal. The frequencies of the corresponding Raman Stokes components in the IR range (from 1193 to 9662 nm) are calculated. The results of the study open the way to form an array of laser frequencies from the IR to green spectral range with a period of 1047 cm–1.

A forward-directed high-efficiency stimulated inelastic light scattering was detected in an aqueous suspension of spherical nanoparticles (nanoballs) of amorphous SiO2 of similar sizes (0.25 μm) with a concentration of 1013 cm-3. In the stimulated scattering spectrum, there was an intense forward directed Stokes component with a frequency shift of 0.54 cm-1, corresponding to the boson peak mode of spherical nanoparticles. The results obtained are of interest for non-equilibrium excitation of spherical particles of similar sizes of different nature present in liquids (clusters, fullerenes, spherical macromolecules, viruses, etc.).

We have studied the optical properties of copper-doped lithium niobate crystals using semiconductor light-emitting diodes and lasers emitting in the visible and ultraviolet spectral regions as excitation sources. The results demonstrate that, at an excitation frequency approaching the frequency of electronic absorption in copper ions, there is discrete resonance Raman scattering in the form of a frequency comb. The observed Raman satellites of discrete light scattering are due to polar longitudinal A1 optical modes of the lithium niobate single crystal. Under excitation by a light-emitting diode with a wavelength of 520 nm, we observe a sharp increase in discrete light scattering intensity in comparison with the photoluminescence excited by shorter wavelength excitation sources.

The photoluminescence (PL) of copper-doped lithium niobate single crystals is studied using different UV–Vis light-emitting diodes and a pulse-periodic laser with a wavelength of 266 nm as excitation radiation sources. With the resonance excitation from a 527-nm light-emitting diode, the intensity of PL increases sharply (by two orders of magnitude). When using a 467-nm light-emitting diode for excitation, the PL spectrum is characterized by the presence of multiphonon lines in the range of 520–620 nm.

The evolution of Raman spectra in a wide range of temperatures that includes the ferroelectric transition point in lithium niobate single crystals is studied for polarization geometry X(ZZ)Y. In this geometry, the soft mode responsible for the phase transition distinguished by 1A1(TO)-type symmetry should appear in the spectra. Experimental studies show that the 1A1(TO) mode interacts resonantly with nonfundamental modes in the low-frequency region of the spectrum. Near the ferroelectric phase transition point, an isofrequency opalescence effect is observed that consists of an abrupt increase in Raman signal intensity at fixed frequencies near the excitation line.

In stimulated Raman scattering spectra in a lithium tantalate single crystal, for the forward scattering geometry, intense Stokes and anti-Stokes satellites are observed. For the first time, stimulated Raman scattering on compound and overtone transitions with an intensity of 10–50% of the fundamental tone has been discovered. The possibility of the formation of coupled antipolar excitations in stimulated Raman scattering in ferroelectric crystals is substantiated theoretically.

Strong sharp lines due to the librational modes characterized by a pseudoscalar symmetry type have been found in the low-frequency Raman spectra of the lattices of glycine and tyrosine amino acids. The intensities of these lines exceed those for Raman scattering in the region of intramolecular vibrations. The spectra of chirally pure and racemic phases of amino acids differ significantly. The results obtained can be used to observe stimulated Raman scattering from the librational modes of crystalline amino acids and monitor the chiral purity of bioactive preparations containing amino acids.

High-Q librational modes have been found to be present in the infrared absorption and Raman spectra of chirally pure L-tyrosine. Such modes can serve as terahertz radiation detectors and generators in chirally pure biostructures.

Raman spectra of the ferroelectric sodium nitrite are recorded over a wide spectral range at different temperatures, including the ferroelectric phase transition interval. The room-temperature Raman spectrum reveals the overdamped А1(z) soft mode which is attributed to the ferroelectric phase transition.

Raman light scattering spectra of a ferroelectric sodium nitrite crystal is studied in the lattice mode region as the temperature is lowered from room temperature to 123 K. The existence of a Raman satellite corresponding to the soft lattice mode, i.e., transverse polar vibration responsible for the ferroelectric phase transition, is established for the first time. It is found that the intensity of the Raman scattering by the pseudo-scalar low-frequency A2 mode exceeds the intensity of other lattice variations by an order of magnitude.

The dispersion relations of hybrid waves—polaritons, scalar bosons (hiddennons) and pseudoscalar bosons (axinons)—in one-dimensional dielectric media are derived with allowance for the resonant interaction between mechanical excitations of crystal lattices and elementary excitations of vacuum. It is shown that in the range of small wave vectors hybrid quasi-particles are formed in dielectric media: polaritons, hiddennons and axinons. For sodium nitrite crystal, dispersion relations of such hybrid quasiparticles are calculated near the center of the Brillouin zone. The resulting dispersion relations of hybrid quasi-particles provide conditions that allow observation of conversion of vacuum photon-like particles into hybrid quasi-particles in dielectrics, and also of parametric light scattering accompanied by the generation of hybrid quasi-particles.

Room-temperature photoluminescence spectra of DNA, ATP, and ADP placed into photon traps are recorded under ultraviolet excitation. It is found that the use of laser ultraviolet pulse-periodic radiation for excitingDNA,ATP, andADP photoluminescence significantly increases their quantum yield and offers the possibility of lasing in these materials.

Optical Raman spectra of a ferroelectric sodium nitrite crystal have been detected in a wide spectrum range at various temperatures, including the region of the ferroelectric phase transition. A manifestation of a transverse soft polar mode of the A 1(z) type responsible for the ferroelectric phase transition has been discovered in the spectrum at room temperature. This mode has been found to become overdamped even far from the ferroelectric phase transition temperature. This mode also appears as a central peak under heating. It has been found that the pseudoscalar mode of the A 2 type has the highest intensity in the Raman spectrum of sodium nitrite. The frequency corresponding to the maximum intensity of this mode in the Raman spectrum varies from 130 cm–1 at 123 K to 106 cm–1 at T = 513 K. A fair agreement of the experimental data for the A 1(z) mode with the Lyddane–Sachs–Teller relation has been established. The polariton curves for the A 1(z) polar mode and the dispersion curves for axinons has been plotted.

A strong increase in the spectral intensity of Raman scattering (Raman opalescence effect) at the polar soft mode, responsible for the instability of the crystalline lattice, near ferroelectric phase transition points in the barium sodium niobate (BSN) crystal was found. Raman opalescence is explained as a consequence of a sharp increase in the amplitude of the transverse A1(Z; TO) polar optical soft mode near the temperature of the ferroelectric phase transition in BSN (Tc = 830 K). Experimental results were obtained using a new experimental technique, based on the construction of isofrequency temperature dependences, when registering the spectral intensity of Raman scattering at fixed frequencies of the spectrometer, near the frequency of the exciting line, for certain polarization geometry. The conditions for observing the effects of Hyper Raman opalescence near the phase transition temperature in the BSN are established.

Both backward and forward directed Stimulated Brillouin Light Scattering (SBLS) are observed in an aqueous suspension of SiO2 nanoparticles with diameters of 100 and 200 nm by using for excitation a second harmonic (λ = 532 nm, 10 ns) of a single (∼0.005 cm − 1) mode YAG : N d 3 + laser. Both backward and forward directed SBLS are characterized by a low beam divergence and typically for a water Stokes shift of ≈0.25 cm − 1. The microscopic explanation of forward directed SBLS in an aqueous suspension of SiO2 spherical nanoparticles is proposed.

Dispersion dependences of electromagnetic waves in tryptophan crystals are constructed taking into account photon-axion conversion processes in the low-symmetry tryptophan crystal field. It is shown that a peculiarity associated with the intersection of dispersion curves of electromagnetic and axion waves appears in the frequency range of unitary polaritons, corresponding to the unity refractive index. In the intersection region, hybrid polariton-axion quasiparticles called axitons are formed. The dispersion relation for axitons in the visible and infrared spectral regions is derived. The conditions for photon-axion conversion near the exciton absorption edge of tryptophan in the ultraviolet spectral region are determined.

Multiple Stokes and anti-Stokes satellites were observed in the spectra of stimulated parametric Raman scattering of light in liquids and crystals when excited by picosecond laser pulses of a YAG: Nd3+ solid-state laser with generation wavelengths of 1064 and 532 nm. The Stokes combination satellites of the infrared range were detected as a result of their conversion into the visible spectral region. The results obtained are of interest for the development of the theory of parametric processes of stimulated Raman scattering of light in crystals and liquids, which is also important for creating efficient laser sources from the ultraviolet to the far infrared.

The work analyzes the isofrequency temperature dependences of Raman scattering near the phase transition point in quartz. Theoretical dependences for the spectral intensity of inelastic light scattering are derived. Coefficients for these dependencies were obtained on the basis of experimental data.

The photoluminescence spectra of aromatic compounds in a photon trap under ultraviolet pulse-periodic excitation are recorded. It is shown that the photoluminescence spectrum shape depends on the material layer thickness in a cell, physical state of the sample, and exciting radiation characteristics: as the layer thicknesses decreases, the intensity is significantly redistributed, which is explained by the transition from spontaneous luminescence to superluminescence.

A Raman spectrum of dry DNA has been recorded in a wide frequency range with a high spatial resolution. The Raman intensity of the low-frequency mode (25 cm−1) of dry DNA is found to exceed the intensity of intramolecular vibrations of nucleic bases and sugar-phosphate backbone by more than an order of magnitude. The position of the low-frequency peak changes with temperature of the DNA under study.

The paper deals with spontaneous scattering in LiNbO3 and LiTaO3 crystals we synthesized to contain different dopants (Mg2+, Zn2+, Gd3+, B3+, Cu+ and others). We investigated photoinduced light scattering patterns in doped LiNbO3 crystals. We recorded Raman spectra at different light scattering geometries and temperatures. We detected pseudoscalar modes in the Raman spectra of doped LiNbO3 and LiTaO3 crystals.

In this paper the micro-Raman spectra of calf DNA for different points of DNA sample have been recorded. The Raman spectra were made with help of difference Raman spectroscopy technique. Raman spectra were recorded with high spatial resolution from different points of the wet and dry samples in different spectral range (100÷4000cm−1) using two lasers: argon (514.5 nm) and helium -neon (632.8 nm). The significant differences in the Raman spectra for dry and wet DNA and for different points of DNA molecules were observed. The obtained data on difference Raman scattering spectra of DNA molecules may be used for identification of DNA types and for analysis of genetic information associated with the molecular structure of this molecule.