ABSTRACT
Additional bands have been discovered for the first time in the Raman spectra of terbium doped lithium niobate crystals. The bands have been determined in the high-frequency region and have been attributed to the overtone states of the second order of polar fundamental modes of the crystal lattice. It has been established that Raman spectrum of terbium doped lithium niobate contains bands with frequencies exceeding the overtones of the highest-frequency fundamental polar modes of A1(Z) and E(X, Y) symmetry types. The observed features of the second-order Raman spectra have been interpreted as a manifestation of bound states of phonons - biphonons.
ABSTRACT
The observation of multifrequency stimulated Raman scattering of light in a thin powder layer of a gyrotropic crystal of sodium bromate when excited by intense ultrashort pulses of the second optical harmonic (λ = 532 nm) of an yttrium aluminum garnet laser is reported. Five Stokes and anti-Stokes satellites corresponding to the excitation of the intramolecular optical mode of NaBrO3 crystal were present in the recorded spectra. In addition, Raman satellites corresponding to the excitation of lattice modes, as well as their combinations with intramolecular modes, were found in the spectra of stimulated Raman scattering. The prospects of using stimulated Raman scattering spectroscopy for express analysis of gyrotropic media: gyrotropic polycrystals, crystalline amino acids, proteins, DNA, etc. have been established.
ABSTRACT
The spectra of stimulated Raman scattering of light in ethanol and in water suspensions containing diamond microparticles with sizes 0.2-0.3 µm were investigated. An excitation radiation source was a pulsed ruby laser with a generation wavelength λ0 = 694.3 nm, a pulse duration τp ≈ 20 ns, a maximum beam energy of Emax = 0.6 J, a spectral width Δν = 0.015 cm-1, and a beam divergence 3.5·10-4 rad. For the first time, the observation of stimulated Raman scattering of light at a boson peak in suspension of diamonds microcrystals with close sizes (0.2-0.3 µm) in a liquid is reported. The corresponding spectra were recorded using a Fabry-Perot interferometer. In this case, the frequency shift of the stimulated Stokes Raman scattering depended on the size of the diamond microparticles introduced into the liquid and amounted to ~1 cm-1. In addition, stimulated Raman scattering by a fundamental optical mode with a frequency shift ν = 1331 cm-1 was observed. In this case, the Raman spectra were recorded using a small-sized spectrometer with a multi-element receiver, detecting radiation in the range of 200-1000 nm. At a sufficiently high intensity of the exciting radiation, the Stokes and anti-Stokes satellites were simultaneously present in the spectrum of stimulated Raman scattering. The obtained results on stimulated scattering of diamond microparticles in liquids are of interest for estimating the sizes of microcrystals from scattering spectra at a boson peak, as well as for creating a frequency comb of emitters based on stimulated Raman scattering with a large frequency shift.
ABSTRACT
Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole-dipole coupling and suppress the ferroelectric order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H2O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole-dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie-Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices.
