Anomalous coherent backscattering of light from opal photonic crystals

We studied coherent backscattering (CBS) of light from opal photonic crystals with incomplete band gaps. We observed a dramatic broadening of the CBS cone for incident angles close to the Bragg condition in the crystals. We modify the conventional CBS theory to incorporate Bragg attenuation resulting from the photonic band structure. By fitting the CBS data with the modified theory, we extract both the disorder-induced light mean-free path and the Bragg attenuation length of the inherent opal photonic crystal.     

One-dimensional opal photonic crystals

One-dimensional opals are 1D self-assembled close packed colloidal crystals consisting of monodisperse colloidal globules. Polystyrene globules with sizes in the 1.9–10 μm range sit on a flat substrate and touch two neighbors in diametrally opposite contact points. These opals are quasi-1D photonic crystals. Optical modes, including whispering gallery modes of individual globules, coupled collective modes, and nanojet-induced modes, are visualized in 1D opals.     

Dispersion of light in opal photonic crystal

The selective reflection spectra of films prepared from the photonic crystal, i.e., synthetic opal, are investigated. It is revealed that the refractive index changes at the boundaries of the photonic band gap. The wave vector is renormalized as a result of the interaction of the light wave with the periodic structure of the crystal, and the dependence of the frequency on the photon wave vector deviates from a linear behavior. The band gap determined from these data is approximately equal to 1.7 × 10¹⁴ Hz.     

Modification of photonic properties in porphyrin-infiltrated opal crystals

Structural, optical and magnetic properties of porphyrin-infiltrated opal hybrid structures were investigated. Bulk samples of synthetic opal were grown by sedimentation technique from colloidal solution of SiO₂ spheres of diameter 250 nm. The structure of the samples was examined by atomic force microscopy. The photonic properties of crystals were investigated by optical measurements in transmission and reflection modes. The stop band was observed in the region 510–550 nm. The photonic properties of synthetic opal crystals were modified by infiltration with aqueous basic solution of iron–porphyrin (FeTPPS) of concentration 1.0 mM. In hybrid samples the absorption bands typical of FeTPPS were observed in the vicinity of the opal stop band. Magnetic properties of FeTPPS-infiltrated opal samples have been studied at 5–300 K in magnetic fields up to 5 T. The FeTPPS-infiltrated opal crystals can be considered as the structures perspective for magnetophotonic devices.     

Surface wave effect on light scattering from one-dimensional photonic crystals

Light scattering and reflection measurements using attenuated total reflection technique for s polarization of the incident light on a finite one-dimensional photonic crystal are reported. Angular specular reflection was measured experimentally to determine, the optimum thickness, the angular position of the surface mode, and the number of bi-layers of the system. It was demonstrated that the position of the surface mode inside the last film is close to the asymptotic value when the number of periods is increased. Spectral reflection measurements were made to determine experimentally the band gap width and measure the dispersion relation of the surface mode inside this band. The corresponding field amplitude was calculated (∣E∣²) showing that in resonant conditions it has a maximum near the surface. The angular dependence of the scattered light measured displays a peak caused by singles cattering and located approximately at the excitation angle of the surface electromagnetic mode. When the incident light is in resonance with the surface electromagnetic wave, it is found experimentally that the scattering of light is enhanced overall by approximately one order of magnitude in comparison with the off-resonance case.     

Slow light in photonic crystals

The problem of slowing down light by orders of magnitude has been extensively discussed in the literature. Such a possibility can be useful in a variety of optical and microwave applications. Many qualitatively different approaches have been explored. Here we discuss how this goal can be achieved in linear dispersive media, such as photonic crystals. The existence of slowly propagating electromagnetic waves in photonic crystals is quite obvious and well known. The main problem, though, has been how to convert the input radiation into the slow mode without losing a significant portion of the incident light energy to absorption, reflection, etc. We show that the so-called frozen mode regime offers a unique solution to the above problem. Under the frozen mode regime, the incident light enters the photonic crystal with little reflection and, subsequently, is completely converted into the frozen mode with huge amplitude and almost zero group velocity. The linearity of the above effect allows the slowing of light regardless of its intensity. An additional advantage of photonic crystals over other methods of slowing down light is that photonic crystals can preserve both time and space coherence of the input electromagnetic wave.     

Spontaneous parametric light scattering in spatially inhomogeneous nonlinear media based on photonic crystals

The emission spectra of nonlinear media with periodical modulation of the second-order susceptibility that are based on synthetic opals infiltrated by Ba(NO₃)₂, LiIO₃, and KH₂PO₄ are studied using radiation with λ = 400 and 407 nm for excitation. The spectral angular distribution of the emission in the range of 420–650 nm is revealed, as well as the dependence of its spectrum on the photonic stop-band parameters and the exciting radiation characteristics. The emission spectrum of samples with a low dielectric contrast has the shape of a symmetric band with a maximum at 525 nm and a half-width of about 100 nm. The observed emission is interpreted as spontaneous parametric light scattering in a spatially inhomogeneous nonlinear medium.     

Stimulated Raman scattering in three-dimensional photonic crystals

The results of experimental studies of stimulated Raman scattering of light (SRS) excited in three-dimensional photonic crystals — synthetic opal matrices infiltrated with Raman active media are presented. It is shown that the SRS threshold in such structures decreases with respect to the SRS threshold in Raman active bulk materials. The influence of the photonic-band structure of the active materials used on the SRS properties is estimated.     

Refraction of light in two-dimensional photonic crystals

Refraction of light at an interface between a homogeneous dielectric and a two-dimensional photonic crystal is studied. Using the isofrequency method, various cases of refraction, including a change in the magnitude and direction of the wave vector of the incident wave, in the refractive indices of the media, and in the mutual orientation of the interface and the translation vectors of the photonic crystal, are investigated. Different types of refraction and the possibilities for realizing negative and multiwave refraction are considered.     

Optical spectra of one-dimensional defect photonic crystals

The effect exerted by defects that represent a local disturbance of the structural periodicity on the band spectrum of a one-dimensional photonic crystal has been investigated. A classification of single defects has been proposed. It has been demonstrated that the position of defect minibands in the band gap of the spectrum of the crystal can be controlled by varying the type of a defect and its location in the crystal structure. The presence of two defects in the structure leads to the formation of two minibands, so that the spacing between the minibands and their intensity depend on the type of defects and on the distance between them.     

Multifrequency stimulated Raman scattering of light in liquid nitrogen infiltrated into 3D photonic crystals

Spectral characteristics of stimulated Raman scattering at least in synthetic opal matrices infiltrated with liquid nitrogen upon excitation by nanosecond laser pulses are studied. The effect of the stop band position on the generation efficiency of anti-Stokes components of stimulated Raman scattering up to the third order is demonstrated. The excitation threshold of stimulated Raman scattering in liquid nitrogen infiltrated into opals is significantly lower in comparison with the generation in bulk samples.     

Bragg scattering induces Fano resonance in photonic crystals

We present a study of a Fano resonance between a narrow Bragg band and disorder-induced continuum in photonic crystals where the continuum is either of the broad band Fabry-Pérot scattering in an imperfect one-dimensional photonic crystal or Mie scattering in an imperfect three-dimensional photonic crystal. Our experimental studies of synthetic opals have demonstrated how the Fano resonance may lead to a transmission spectrum exhibiting a Bragg dip with an asymmetric profile or a Bragg rise.     

Dynamic control of light localization in photonic crystals

Localization of light in a one-dimensional finite dielectric with a periodically modulated refractive index and two local periodicity perturbations is considered. It is shown that phase modulation of incident light can be used to localize it at different spatial points of the system considered.     

Stimulated Raman scattering of light in artificial opal filled by water

We investigate stimulated scattering of light in globular photonic crystals infiltrated by water. Excitation of stimulated scattering of light is realized using powerful ultrashort (70 ps) laser pulses with an energy of 35 mJ and a frequency repetition of 15 Hz. We use the second-harmonic generation (532 nm) of the master oscillator and amplifier with a wavelength of 1064 nm. The photonic crystals under study are artificial opals filled by water or ethanol. We characterize the sample structures employing an electronic microscope along with the fiber-optics reflectance-spectroscopy technique. Photonic crystals have a stop band near the spectral positions of the exciting line (532 nm) and the first satellite of stimulated Raman scattering of light in water (649 nm). We observe a substantial reduction of the threshold of stimulated Raman scattering of light in water-infiltrated artificial-opal matrices in comparison with that of pure water. Such a reduction is explained as the result of a sharp increase in the photonic density of states near the stop-band edges of investigated photonic crystals. The reduction in the threshold of stimulated Raman scattering of light in water-infiltrated artificial-opal matrices opens up the opportunity to observe stimulated Raman scattering in numerous water media, including water solutions, biological and medical samples, heavy waters, and others.     

Electro-optic behavior of liquid-crystal-filled silica opal photonic crystals: effect of liquid-crystal alignment

Photonic crystals made of nematic liquid crystal intercalated into the void space of close-packed silica spheres (synthetic porous opal) exhibit significant electric-field-induced shift of the optical Bragg reflection peak when the liquid crystal has the long molecular axis oriented parallel to the sphere surfaces. No such effect is observed for comparable fields when the long-axis orientation is normal to the sphere surfaces.     

高质量胶体晶体薄膜的快速制备及表征

通过控制温度和湿度，用垂直沉积法（vertical deposition method）快速制备出了可精确控制样品的厚度、在较大范围呈现好的有序性的密排结构的聚苯乙烯（PS）胶体晶体 薄膜.利用透射电子显微镜直观准确地确定了样品为面心（fcc）密排结构.通过控制样品干燥速度和加温处理，胶体颗粒排列更加有序,并且克服了胶体晶体干燥后易碎和在水等溶 剂中容易再分散等缺点，为胶体晶体实际应用创造了条件. 关键词： 胶体晶体薄膜 垂直沉积法 面心密排结构 再分散     

Raman scattering of light in N-benzylaniline crystals

Single crystals of N-benzylaniline (C₆H₅-CH₂-NH-C₆H₅) have been grown, X-ray structural analysis of these crystals has been performed, and their symmetry has been identified as corresponding to the space group C _2h ⁵ . Raman spectra of N-benzylaniline single crystals in polarized light for different geometries of the experiment have been analyzed. Frequencies and symmetry of lattice phonons have been determined.     

Nonlinear molecular scattering of light in crystals

Nonlinear molecular scattering of light in crystals KDP and LiIO₃ is studied experimentally and theoretically. Spectral distributions of scattered radiation intensity are obtained. Experimental results are compared with theory.     

Quantitative analysis of subdiffractive light propagation in photonic crystals

We present a qualitative study of the subdiffractive light beam propagation in photonic crystals, based on the theoretical analysis of full Maxwell equation system beyond the slowly varying envelope and paraxial approximations. We calculate the zero diffraction curve in the parameter space, we calculate the weak asymptotical broadening (spreading in transverse direction), and we also analyze the dependence of subdiffractive propagation on the polarization orientation (both for TM and TE polarization).