P. P. Sverbil

Raman scattering study of NaNO2-infiltrated opal photonic crystals

We have studied light scattering in synthetic opal crystals infiltrated with ferroelectric sodium nitrite, NaNO2, and have analyzed simple models for the energy band structure of photonic crystals. Expressions have been derived for the group velocity of photons whose energy is close to the photonic band gap. Our results indicate that the infiltration of photonic crystals with NaNO2 markedly increases the Raman scattering intensity.

Raman scattering by longitudinal and transverse optical vibrations in lithium niobate single crystals

Raman spectra of single-domain congruent lithium niobate crystals have been measured in forward-axis and backscattering geometries, with excitation laser light propagating along or across the ferroelectric axis Z. We have identified excitation conditions for transverse and longitudinal A1(Z) polar optical modes in room-temperature Raman spectra. The general aspects of the excitation of Raman spectra have been studied in several polarization geometries: Z(XX; YY; XY)Z, Z(XX; YY; XY)

Secondary radiation of synthetic opals loaded by the sodium nitrite ferroelectric

\bar Z

Second optical harmonic near the surface of ferroelectric photonic crystals and photon traps

; X(ZZ)X; Y(ZZ)Y, and X(ZZ)Y. The excitation conditions for coherent longitudinal and transverse modes in lithium niobate single crystals in the case of stimulated Raman scattering have been analyzed.

Local spectroscopy of band gaps in ferroelectric photonic crystals

This paper reports on a comparison of transmission, reflection, and secondary radiation spectra of unloaded synthetic opals and samples filled with the sodium nitrite ferroelectric (NaNO2). The radiation is provided by semiconductor light-emitting diodes operating in the ultraviolet and visible spectral regions. Selective excitation of slow electromagnetic waves in a photonic crystal, an effect observed when the exciting radiation frequency approaches the stop-band edge, is studied.

Optical properties of three-dimensional magnetic opal photonic crystals

This paper reports on the results of experimental investigations of the generation of the second optical harmonic localized in a thin subsurface layer of ferroelectric photonic crystals and photon traps. To excite the second optical harmonic, a KGW: Yb solid-state pulsed-periodic laser generating the radiation with a wavelength of 1026 nm in a form of pulses ∼10−13 s long with a repetition frequency of 200 kHz at the average power of 0.1–3.5 W and power density of ∼109−1012 W/cm2 in a spot less than 100 μm in diameter focused near the surface was used. Ferroelectrics, notably, barium titanate or sodium nitrite, were introduced into the pores between SiO2 nanoglobules. It is established that the maximal conversion efficiency of the exciting radiation into the second optical harmonic was several percents. The generation characteristics of the second optical harmonic near the surface of photonic crystals filled with ferroelectrics are compared with the generation of the second optical harmonic in ferroelectric photon traps of barium titanate ceramics and sodium nitrite microcrystals.

Raman scattering in dried DNA and crystalline amino acids

We have measured visible to near-UV reflection spectra of opal photonic crystals infiltrated with ferroelectrics: barium titanate, sodium nitrite, potassium iodate, and triglycine sulfate. An experimental procedure has been developed for the infiltration of various ferroelectrics into opal pores through laser ablation and laser implantation. Using a fiber-optic probe, we were able to analyze surface reflection spectra of photonic crystals with a 0.2-mm resolution. A deuterium lamp was used as a broadband UV source, which allowed us to observe both the first and second [111] photonic band gaps in the reflection spectrum of opal crystals.

Spectra of secondary emission during generation of optical harmonics in globular photonic crystals

We have studied the optical properties of opal photonic crystals infiltrated with the M0.35Zn0.65Fe2O4 (M = Ni, Co) ferrites. The crystals consisted of amorphous SiO2 nanospheres. The visible reflectivity spectra of the crystals were used to determine parameters of their photonic band gap and their refractive index.

Lowering of stimulated Raman scattering threshold as a result of light capture

Raman spectrum characteristics of dried deoxyribonucleic acid (DNA) and two types of crystalline amino acids (L-lysine, D-asparagine) are compared in a wide range of frequencies, including the regions of lattice (7 to 200 cm−1) and intramolecular (200 to 4000 cm−1) vibrations. It is found that the spectral position of the low-frequency band in the Raman spectrum of DNA with a peak near 26 cm−1 correlates with the Raman spectrum of high-Q low-frequency modes that manifest themselves in the crystalline amino acids under investigation. The low-frequency band of DNA refers to a twist-like vibrational mode of nucleobases. The intensities of this DNA mode and the high-Q lattice modes of the crystalline amino acids L-lysine and D-asparagine are several times as high as those of the Raman lines corresponding to the intramolecular modes. Resonant coupling of low-frequency modes of DNA and amino acid molecular chains is analyzed.

Isofrequency Opalescence in Ferroelectrics

Secondary emission spectra of globular silica photonic crystals when their surfaces were exposed to laser pulses 250 fs long at a power density to 1 TW/cm2 have been studied. Optical harmonics and plasma emission were detected in this case. For the opal matrix containing pores filled with air, in the reflection mode, the third optical harmonic with a conversion efficiency of ∼10% arises. The highest conversion efficiency for exciting radiation with wavelengths of 1026 or 513 nm is implemented when the frequencies of the exciting radiation or the second harmonic are near the stop band edge. In globular photonic crystals filled with sodium nitrite or barium titanate ferroelectrics, the second optical harmonic is observed. The exciting radiation conversion efficiency to the second optical harmonic was a few percent and depended on the frequency of exciting radiation and photonic crystal globule diameters. It is found that the plasma emission intensity increases with the exciting radiation power density. The dependences of the intensity of the second and third optical harmonics on the pump intensity are constructed for various photonic crystal globule diameters.