Bypassing and cutting through 1D photonic crystals by ultra-shallow wet-etched resonant gratings

The electromagnetic field in subwavelength resonant diffractive optical elements is so concentrated that a very shallow surface corrugation obtained by wet chemical micro–nano-etching is sufficient to give rise to high contrast diffraction effects allowing a high wavelength-, polarization- or transverse-mode-selectivity which is not achievable by conventional diffractive elements. Two examples of polarizing laser mirrors at both extremes of the optical spectrum with wet-etched grating bypassing and cutting through the 1D photonic crystal are demonstrated.     

Dynamic theory of resonant X-ray Bragg diffraction in perfect crystals

An exact solution is found to the problem of mirror reflection and resonant Bragg diffraction of X rays in a perfect crystal. An anomalous transmission of radiation with the energy close to the K-edge absorption of the atoms is shown to be feasible.     

Defects and diffraction in photonic crystals

Photonic crystals are very promising because they provide the ability to create high performance microcavities with a high quality factor for a small modal volume. These cavity modes are obtained by creating defects in the periodicity and the defect design must be optimized to obtain the highest transmission. We investigate defect properties in the graphite structure by varying the size of some cylinders. Using the Transfer Matrix Method, we calculate the in-plane diffraction of defect rows and show how this diffraction affects the transmission of the cavity mode.     

Optical waves in photonic crystals and the photonic flame effect

We present the coupled-mode equations for inclined waves in photonic crystals. Among the eigenmodes, we focus on the evanescent modes. We consider the conjugation of the waves at the interface of the crystal and its metallic substrate. We underscore the role of resonant coupling of the fields at this interface and briefly discuss the field structure in the open space.     

Extension of the resonant scattering technique to liquid crystals without resonant element

We report X-ray resonant scattering experiments performed on the prototype liquid-crystalline compound MHPOBC doped with a chemical probe containing a resonant atom (selenium). We determined directly for the first time the microscopic 3- and 4-layer structure of the ferrielectric subphases ( SmC_FI1^* and SmC_FI2^*) present in MHPOBC. Despite the low fraction of the selenium probe, the resonant signal is strong enough to allow an unambiguous determination of the basic structure of the ferrielectric subphases. These experiments demonstrate that the resonant scattering technique can be extended to liquid crystalline materials without resonant element and may stimulate new studies. A non-resonant Bragg reflection was also found in the SmC_FI1^* phase in pure MHPOBC, consistent with the 3-layer distorted model, but never detected before.     

Molière's theory of multiple scattering applied to the spark chamber

The statistical theory of the Onsager symmetry-relations given by R.T.Cox is extended to non-isolated systems. The symmetry-relations are identical to the existence of a detailed balance. The conditions for the existence of a detailed balance are discussed. These conditions are microscopic reversibility in connection with a special type of correlation between the system and its surroundings. This type of correlation characterizes the thermal contact with thermal surroundings. In the appendix the process of pumping in a three-level-maser is discussed as an example for non-existence of a detailed balance in spite of microscopic reversibility.     

Interference of additional modes in spectra of opal-like photonic crystals in the multiple diffraction regime

The mechanisms of formation of Bragg reflectance and transmittance spectra have been investigated for films of three-dimensional opal-like photonic crystals. Attention has been drawn to the fact that the spectra exhibit an additional short-period interference structure of the novel type due to the multiple Bragg diffraction of light. The spectra have been calculated in the framework of the dynamical three-wave diffraction model taking into account strong spatial modulation of the dielectric function. It has been found that short-period oscillations appear in the spectra due to the spatial quantization of additional modes with a low group velocity.     

On the theory of diffraction of light in photonic crystals with allowance for interlayer disordering

Electrodynamic Green’s functions are used to construct an analytical theory of the Bragg diffraction of polarized light in photonic crystals having a close-packed structure. For opal-based photonic crystals, the Bragg diffraction intensity is calculated with allowance for permittivity periodic modulation and for the presence of an optical crystal boundary and interlayer disordering, which usually appears during sample growth. A comprehensive study is made of the effect of the structure disorder caused by the random packing of growth layers on diffraction. For a random constructed twinned fcc structure, the average structure factor and the scattering (diffraction) cross sections (which are dependent on the linear polarization of the incident and scattered waves) are calculated. Numerical examples are used to show that the theory developed can be applied to analyze and process experimental diffraction patterns of real photonic crystals having a close-packed structure disordered in one direction.     

On the ability of resonant diffraction gratings to differentiate a pulsed optical signal

The passage of an optical pulse through a resonant grating is considered. The conditions under which the resonant grating differentiates the envelope of the incident pulse are determined. It is shown that the necessary condition for computing the k-order derivative is the presence of k resonances in the transmission spectrum of the grating in the vicinity of the central frequency of the incident pulse. A method is described for constructing the stacked structure for computing the kth derivative on the basis of repetition of the structure for computing the first derivative. The results of numerical simulation of diffraction of the pulse from the analyzed structure for computing the first, second, and third derivative are presented.     

Photonic resonant transmission in the quantum-well structure of photonic crystals

A photonic quantum-well is constructed by sandwiching a uniform medium between two photonic barriers due to the photonic band gap mismatch, similar to electronic quantum well. The transmission coefficient is calculated by a plane-wave expansion method in combination with multiple-scattering techniques. The transmission peaks indicate that some photonic states exist in a quantized way, satisfying a quantized frequency relation. We also show that the finite photonic potential barrier plays different confined roles on the different photonic levels. The positions and number of the resonant peaks can be artificially tuned by varying the well width. By appropriately choosing the parameters of the well and barrier, a high-quality multichannel filtering can be achieved.     

Comparison between a thin matrix decomposition method and the rigorous coupled wave theory applied to volume diffraction gratings

Diffraction gratings have been an interesting field during the last decades. A great deal of research has been done in order to understand how light propagates inside diffraction gratings. Since its formulation, the Rigorous Coupled Wave Theory (RCWT) has been applied to different periodic structures providing a basis to check the validity of approximate theories, such as Kogelnik's coupled wave theory or the coupled wave theory neglecting second derivatives. In this work we will compare the results of the diffraction efficiencies of the first and second orders at second on-Bragg replay angular condition, obtained by using an analytical formula provided by Alferness using an approximate thin-matrix decomposition method (TMDM) with the results obtained by using the RCWT. Good agreement between the results obtained using TMDM and the RCWT were found.     

Investigation of magnetostatic waves in photonic crystals

The frequency dependence of the Lyapunov index in the bandgap of a magnetic photonic (spin) crystal has been experimentally determined for the first time.     

Color of shock waves in photonic crystals

Unexpected and stunning new physical phenomena result when light interacts with a shock wave or shocklike dielectric modulation propagating through a photonic crystal. These new phenomena include the capture of light at the shock wave front and reemission at a tunable pulse rate and carrier frequency across the band gap, and bandwidth narrowing as opposed to the ubiquitous bandwidth broadening. To our knowledge, these effects do not occur in any other physical system and are all realizable under experimentally accessible conditions. Furthermore, their generality make them amenable to observation in a variety of time-dependent photonic crystal systems, which has significant technological implications.     

X-ray diffraction diagnostics methods as applied to highly doped semiconductor single crystals

Si(As, P, B) and GaSb(Si) single crystals are used as examples to demonstrate the possibilities of methods of X-ray diffraction for the diagnostics (examination of a real structure) of highly doped semiconductor crystals. Prominence is given to characterizing the state of impurity: whether it is in a solid solution or at a certain stage of its decomposition. An optimum combination of X-ray diffraction methods is found to obtain the most complete information on the microsegregation and structural heterogeneity in crystals with low and high X-ray absorption. This combination is based on X-ray diffraction topography and X-ray diffractometry methods having an increased sensitivity to lattice strains.     

Role of confined Bloch waves in the near field heat transfer between two photonic crystals

The near field heat transfer between two finite size one-dimensional photonic crystals separated by a small vacuum gap and maintained in nonequilibrium thermal situation is theoretically investigated. The main features of this electromagnetic transfer are discussed and compared with what is generally observed with media that support surface polaritons. It is shown that the presence of surface Bloch waves can significantly enhance heat transfers beyond the far field limit for both polarization states of electromagnetic field at subwavelength separation distances. A specific attention is addressed to the consequence of the slopes of surface Bloch waves dispersion curves on the heat transfer. In particular, it is shown that the localization of surface Bloch waves close to the light line allows to observe a transfer exaltaion at larger separation distances than the Wien wavelength. These results could open new possibilities for the development of innovative near-field technologies such as near-field thermophotovoltaic conversion, plasmon assisted nanophotolitography or near-field spectroscopy.     

Bloch waves and non-propagating modes in photonic crystals

We investigate the propagation of electromagnetic waves in finite photonic band gap structures. We analyse the phenomenon of conduction and forbidden bands and we show that two regimes are to be distinguished with respect to the existence of a strong field near the interfaces. We precise the domain for which an effective medium theory is sounded.