rus
The possibility to create materials with the reverse refractive index in the visible range is subject to criticism. The article invites to discussion, coming to an end with the description of Goos-Henchen effect.
Теги: goos-henchen effect metamaterials photonic crystals reverse refractive index метаматериалы обратный показатель преломления фотонные кристаллы эффект гуса-хенхен
In order to answer the question, whether it is possible to make metamaterial for visible portion of wavelengths or not, it is necessary to separate bold forecasts of a number of scientists from actually observed optical effects. Dealing with their physical essence and discarding the methods of their mathematical modeling, we will continue to consider a number of observed optical effects.
2.8. BRAGG-WOLF CONDITION
This condition defines the provision of interferential maxima of the X-rays disseminated by crystal without wavelength change. Bragg-Woolf condition was found in 1913 independently from each other by the English scientist W. L. Bragg and Russian scientist G. V. Wolf soon after discovery of X-ray diffraction by the German scientist M. v. Laue et al. [54, 55]. According to Bragg-Wolf theory, intensity maxima (diffraction peaks) arise when X-rays are reflected from a system of the parallel crystallographic planes when the beams reflected by different planes of this system have path-length difference equal to integral number of wavelengths (fig. 17). Bragg-Wolf condition can be written down as follows: 2dsinθ = mλ, where d is an interplanar distance, θ is a gliding angle, i. e., an angle between the reflecting plane and the falling beam, λ is the wavelength of X-ray radiation and m is the so-called order of reflection (positive integral number).
Bragg-Wolf condition allows defining interplanar distances d in a crystal since λ is usually known, and angle θ (Bragg angle) is measured experimentally. Bragg-Wolf condition is received without refractive effect for the boundless crystal having ideal periodic structure. In fact, the diffracted radiation propagates in a final angular interval θ ± Δθ, where the width of this interval is defined in a kinematic approach by a number of the reflecting nuclear planes (i. e., it is proportional to the crystal linear dimensions), similar to a number of strokes of diffraction grating.
Distortions of crystal lattice, depending on their character, cause change of angle θ, or Δθ increase, or both in the same time. Bragg-Wolf condition is a starting point of researches in X-ray structure analysis, X-ray study of materials, X-ray topography; it remains true for diffraction of γ-radiation, electrons and neutrons in crystals, for diffraction in layered and periodic structures of radio- and optical radiation, as well as acoustic. In nonlinear optics and quantum electronics, when describing parametrical and inelastic processes, different conditions of wave spatial synchronism, similar to Bragg-Wolf condition, are applied.
2.9. GROUP VELOCITY OF LIGHT
For monochromatic light beam, the concept of phase velocity Vph, the traverse velocity of certain phase of wave in the set direction, is used. If the medium refractive index depending on frequency is equal to n(ω), then Vph= c/n(ω). The phase velocity does not correspond to real physical propagation of light.
Let us consider the way the pulse containing several different frequency components (with narrow content frequency) passes through the linear medium where the superposition principle is observed. The medium with the refractive index depending on frequency, e. g., carbon sulfur [56], changes the nature of interference, forcing the waves of each separate frequency to extend at their phase velocity. Such movement is described using the group velocity Vg = c/(n(ω) + ν∙dn/dω)=c/ng, where ng is a group refractive index. Group velocity of waves is the motion velocity of group of waves causing wave formation localized in space of superposition of plane simple harmonic waves with near-frequencies values (ω) and wave vectors (k) in each moment of time.
Under strong dispersion, group velocity can be some orders less than light velocity in vacuum. If the medium does not possess dispersion, all harmonious waves propagate at the same phase velocity, and the package behaves as a strictly stationary wave, i. e., its group velocity coincides with phase velocity.
The normal and abnormal dispersions of light can be distinguished.
• Normal (negative) dispersion of the medium – when the refractive index increases with growth of frequency of harmonious wave (dn/dω>0). Group velocity is less than the phase velocity; long waves propagate faster than the short ones. Examples of mediums with normal dispersion: substances, transparent for optical waves, wave guides, isotropic plasma.
• Abnormal (positive) dispersion of the medium (dn/dω<0) – when the group velocity of signal exceeds its phase velocity: dω/dk > ω/k (long waves propagate more slowly than the short ones). Abnormal dispersion is characteristic for capillary waves on water surface (Vg = 2Vph), for electromagnetic and acoustic waves in mediums with resonance absorption, and also, under certain conditions, for waves in periodic structures (crystals, slow-wave circuits, etc.). Thus, the situation where group velocity is directed opposite to the phase velocity is possible. The waves possessing this property are called reverse waves. Abnormal dispersion is observed within bands or lines of absorption, normal dispersion is observed far from own lines of absorption.
Group velocity determines the velocity and direction of energy transfer by waves. In anisotropic mediums (in crystals, in plasma, in constant magnetic field) where the number of waves depends on frequency and direction of propagation, group velocity is defined as vector derivative Vg = dω/dk, and usually does not coincides in the direction with phase velocity. In mediums with strong absorption instead of group velocity, the value characterizing the velocity of energy transfer Ven = <S> / <W>, where <S> is the average energy flux density, and <W> is the average density of energy in waves, is introduced. In transparent mediums, Ven and Vg values coincide. According to the relativity theory, group velocity cannot exceed the velocity of propagation of light in vacuum [57–60].
2.10. PHOTONIC CRYSTALS
Much attention is paid to photonic crystals (PC), the structures where dielectric permittivity is modulated with the period, comparable with the wavelength of light [61]. Bragg diffraction of intrinsic electromagnetic conditions of Bloch[5] type on the border of Brillouin zone[6] of such structures leads to emergence of photonic band gap for radiation [62, 63].
Does it sound difficult? Let us try to simplify and reformulate.
PCs are the structures consisting of periodically alternating materials (fig. 18) when passing EMI through which Bragg diffraction arises (fig. 17) on periodically alternating borders of layers with different dielectric permittivity. This periodicity, by analogy with electronic zonal structure in regular crystal lattice, causes emergence of "photonic band gap", i. e., spectral area within which propagation of light is suppressed in all or in some chosen directions of PC.
When scales of modulation of dielectric permittivity and wavelength of probing radiation coincide, transmission spectrums contain the characteristic bands caused by Bragg reflection of electromagnetic waves. Manifestation of photonic properties is also met in wildlife (fig. 19). The irisation phenomenon, characteristic for PC (iridescent play of light) is observed in some butterflies (Vanessa kershawi, Morpho rhetenor), sea worm (Genus aphrodita) and in some other types of organisms [65].
Opal is one of the gemstones demonstrating PC properties. This mineral is characterized in various play of light, i. e., opalescence[7], and represents silicon dioxide hydrogel SiO2∙nH2O with variable water content and has the following chemical composition,% wt.: SiO2 – 65–90, H2O – 4.5–20, Al2O3 – up to 9, Fe2O3 – up to 3, TiO2 – up to 5. Sometimes opals have NiO, MnO2 impurities, organic substance. Opals can be colorless or have different colors due to impurities. Their refractive index is 1.44–1.46.
By means of electronic microscopy it was established that jeweler’s opals consist of spherical particles, homogeneous by the size, α-SiO2 (fig. 20) with a diameter of 150–450 nm which, in turn, are formed of smaller globular structures with a diameter of 5–50 nm. Voids of spheres packaging α-SiO2 are filled with amorphous silicon dioxide. Intensity of diffracted light is defined by "ideality" of microspheres packaging and distinction in refractive indices of crystal and amorphous silicon dioxide. The most noticeable irisation is observed for black opals, where distinction in refractive indices makes ~0.02.
PCs are of interest both to basic researches, and to different applications: in optical interconnection, laser technologies, for creation of essentially new appliances and devices. For example, it is possible to create new devices for control of luminous fluxes. Possibilities of management of group and phase velocity of light pulses, and also increase in efficiency of nonlinear and optical processes in such structures cause perspectives of PCs use in telecommunication systems (light filters, miniature wave guides, wavelength converters) [65].
Coverings and paints based on colloid microspheres are widely used. When they dry up, the film is formed opalescent in the sun at change of light incidence angle (especially popular for automotive industry).
It is considered that in the near future photons can already "replace" electrons not only in the information transfer systems, but also in computers (projects on creation of optical computer are under development) that will lead to revolutionary changes in all information technology. Use of PCs in designing of telecommunication systems can promote decrease in attenuation coefficient of optical fibers, creation of low-threshold laser radiators (visible and near Infrared ranges) and superfast optical switches of information flows.
From the point of view of achievement of required photon properties, synthetic opal-based nanocomposites filled with semiconductor materials are very perspective. It is caused both by low cost and technological effectiveness of preparation of relatively perfect opals and opal-based composites with thickness over 100 and even 1000 structural cells, and possibility of variation of their optical properties.
2.11. BIREFRINGENCE. KERR EFFECT
Birefringence is the effect of splitting in anisotropic mediums of ray of light into two components. For the first time the effect was found on crystal of Icelandic spar. If the ray of light is incident perpendicularly to crystal surface (fig. 21), it is split into two beams. The first beam continues to propagate directly and is called ordinary (o - ordinary), the second deviates and is called extraordinary (e - as extraordinary). As a result, two waves having mutually perpendicular linear polarization and diverging with different velocitys (respectively, with different indices of refraction) occur in the crystal.
The difference of refractive indices of two formed waves is used to characterize birefringence: Δn = no – ne. On the exit from crystal phase shift occurs due to different velocity.
Kerr effect is the emergence of birefringence in optically isotropic substances (liquids, glasses, crystals with the center of symmetry) under the influence of constant electric field. The isotropic substance placed in electric field becomes anisotropic, gaining properties of uniaxial crystal. Birefringence value Δn is proportional to square of electric field intensity E: Δn = nkE2, where n is refractive index of substance in lack of field, k is Kerr constant.
2.12. GOOS-HДNCHEN EFFECT
Goos-Hдnchen (GH) effect represents longitudinal shift of reflected beam in the conditions of total internal reflection relative to location determined by ray optics (fig. 22). This effect was discovered in 1943 by F. Goos and H. Hдnchen for multibeam interference in a glass plate. The observed shift was 1–2 λ at the wavelength of 578 nm.
One of the approaches to GH shift explanation was suggested in work [66]. With total internal reflection on dielectric surface, there is exponential attenuating evanescent field (see section 2.5). The energy flow through the plane, perpendicular to the plane of beam incidence and interface of two mediums, is not equal to zero, and the intensity of the incident and reflected beams are identical. In this case the law of energy conservation is true only in case of shift of reflected beam.
There are a number of publications [67–74] where the authors argue on negative GH shift. The majority of these works is theoretical, i. e. authors model negative GH shift in different mediums (absorbing mediums, Me surfaces) and under different incidence angles. Experimental confirmation of negative GH shift would prove the existence of NIM. And now M. Merano et al. [73] declare experimental confirmation of existence of negative GH shift in under conditions of reflection from gold film. However, surprisingly, the values of negative shift Dp (shift for p-polarized light) and positive shift Ds (for s-polarized light) are not specified in the text of article. Instead the difference Dp – Ds is given becoming negative with significant incidence angles (laser beam slides on gold film surface). One can only guess why the authors have presented experimental data in such form and what they have obtained in reality. Whether negative shift was recorded or simply shift Ds exceeded shift Dp? Experimental data in work [74] where the difference ΔTM – ΔTE is analyzed (TM is p-polarized light, and TE is s-polarized light) are similarly presented.
It should be noted that nowadays the researchers have not managed to confirm the existence of negative GH shift experimentally.
The list of the most interesting optical effects concerning EMI passing through substance can be continued. For example:
• parametrical dispersion of light – inelastic dispersion of light in homogeneous nonlinear medium where the parameters are modulated by light wave;
• Mandelstam-Brillouin dispersion – the dispersion of light on adiabatic fluctuations of density of condensed mediums which is followed by frequency change;
• Tyndall dispersion – elastic dispersion of light by non-uniform mediums;
• multiphoton absorption – interaction of EMI with substance where several photons are absorbed in one elementary act.
But these should be the subjects of other publications.
CONCLUSION
The first part of the overview concerned the NIMs and their critical analysis. Actually observed complex optical effects were briefly described in the second and third parts. Analyzing the material stated in the first part of article, it is possible to draw conclusion that NIM operating in the visible range and corresponding to Veselago and Pendry assumptions/predictions will not be created.
Modern researchers need to learn to distinguish the real-life complex, unusual phenomena (effects) from the foggy assumptions and hypotheses based, first of all, on ambitions of their authors. It is a very thin edge demanding the researchers to possess profound knowledge in subject domain, intuition in critical analysis of any new information and at the same time flexible thinking and ability to perceive new information, positively reacting to criticism.
One of the main directions of development of modern nanotechnologies is based on use of unique properties of the spatially arranged nanostructures and creation of optical analogs of elements of microelectronics on their base (conductors, diodes, transistors, memory elements, etc.). Such researches have ultimate goal to develop element base for creation of quantum computers and neural networks. And though the current level of development of technologies is still very far from direct implementation of such projects, it is possible to note undoubted importance of this area for creation of qualitatively new computing systems.
As for researches on creation of different composition materials, they, undoubtedly, will yield practical result [75–89]. For example, composites with nanoparticles (nanotubes, nanofibres) or submicronic particles are applied in Stealth technology, for creation of thermophotoelectric cells, photodetectors (sensors), for radiation cooling/heating of optoelectronic devices, in spectroscopy of huge Raman scattering, for manufacturing LC devices.
Imperceptibly for most of the readers, the researchers have shifted from the area of practical physics into the area of abstract mathematics. Therefore, the criticism concerning predictions for existence of metamaterials in the field of visible light remained almost unnoticed because of a large number of theoretical works in favor of such possibility.
[5] Bloch wave is a wave function of the particle moving in periodically non-uniform medium (crystal).
[6] Brillouin zones are the ranges of values of wave vector k, where energy of electrons changes continuously, and discontinues on the borders.
The wave vector k is one of the main characteristics of electron condition in a solid body. According to the band theory, the electron in crystal cannot have ionization continuum of values of energy, therefore the dependence of energy of electrons E(k) should not have sites corresponding to band gaps, i. e. curve E(k) should have discontinuities in some points.
The physical sense of the Brillouin zone borders is that they show such values of wave vectors or electron quasi-momentums where the electronic wave cannot propagate in a solid body [64].
[7] Ability of a mineral to emit multi-colored highlight from its surface (iridescence, iridescent change of colors). The effect is caused by the interferential phenomena connected with the regular structure of mineral, corresponding to lengths of waves of visible light by scale of frequency.
2.8. BRAGG-WOLF CONDITION
This condition defines the provision of interferential maxima of the X-rays disseminated by crystal without wavelength change. Bragg-Woolf condition was found in 1913 independently from each other by the English scientist W. L. Bragg and Russian scientist G. V. Wolf soon after discovery of X-ray diffraction by the German scientist M. v. Laue et al. [54, 55]. According to Bragg-Wolf theory, intensity maxima (diffraction peaks) arise when X-rays are reflected from a system of the parallel crystallographic planes when the beams reflected by different planes of this system have path-length difference equal to integral number of wavelengths (fig. 17). Bragg-Wolf condition can be written down as follows: 2dsinθ = mλ, where d is an interplanar distance, θ is a gliding angle, i. e., an angle between the reflecting plane and the falling beam, λ is the wavelength of X-ray radiation and m is the so-called order of reflection (positive integral number).
Bragg-Wolf condition allows defining interplanar distances d in a crystal since λ is usually known, and angle θ (Bragg angle) is measured experimentally. Bragg-Wolf condition is received without refractive effect for the boundless crystal having ideal periodic structure. In fact, the diffracted radiation propagates in a final angular interval θ ± Δθ, where the width of this interval is defined in a kinematic approach by a number of the reflecting nuclear planes (i. e., it is proportional to the crystal linear dimensions), similar to a number of strokes of diffraction grating.
Distortions of crystal lattice, depending on their character, cause change of angle θ, or Δθ increase, or both in the same time. Bragg-Wolf condition is a starting point of researches in X-ray structure analysis, X-ray study of materials, X-ray topography; it remains true for diffraction of γ-radiation, electrons and neutrons in crystals, for diffraction in layered and periodic structures of radio- and optical radiation, as well as acoustic. In nonlinear optics and quantum electronics, when describing parametrical and inelastic processes, different conditions of wave spatial synchronism, similar to Bragg-Wolf condition, are applied.
2.9. GROUP VELOCITY OF LIGHT
For monochromatic light beam, the concept of phase velocity Vph, the traverse velocity of certain phase of wave in the set direction, is used. If the medium refractive index depending on frequency is equal to n(ω), then Vph= c/n(ω). The phase velocity does not correspond to real physical propagation of light.
Let us consider the way the pulse containing several different frequency components (with narrow content frequency) passes through the linear medium where the superposition principle is observed. The medium with the refractive index depending on frequency, e. g., carbon sulfur [56], changes the nature of interference, forcing the waves of each separate frequency to extend at their phase velocity. Such movement is described using the group velocity Vg = c/(n(ω) + ν∙dn/dω)=c/ng, where ng is a group refractive index. Group velocity of waves is the motion velocity of group of waves causing wave formation localized in space of superposition of plane simple harmonic waves with near-frequencies values (ω) and wave vectors (k) in each moment of time.
Under strong dispersion, group velocity can be some orders less than light velocity in vacuum. If the medium does not possess dispersion, all harmonious waves propagate at the same phase velocity, and the package behaves as a strictly stationary wave, i. e., its group velocity coincides with phase velocity.
The normal and abnormal dispersions of light can be distinguished.
• Normal (negative) dispersion of the medium – when the refractive index increases with growth of frequency of harmonious wave (dn/dω>0). Group velocity is less than the phase velocity; long waves propagate faster than the short ones. Examples of mediums with normal dispersion: substances, transparent for optical waves, wave guides, isotropic plasma.
• Abnormal (positive) dispersion of the medium (dn/dω<0) – when the group velocity of signal exceeds its phase velocity: dω/dk > ω/k (long waves propagate more slowly than the short ones). Abnormal dispersion is characteristic for capillary waves on water surface (Vg = 2Vph), for electromagnetic and acoustic waves in mediums with resonance absorption, and also, under certain conditions, for waves in periodic structures (crystals, slow-wave circuits, etc.). Thus, the situation where group velocity is directed opposite to the phase velocity is possible. The waves possessing this property are called reverse waves. Abnormal dispersion is observed within bands or lines of absorption, normal dispersion is observed far from own lines of absorption.
Group velocity determines the velocity and direction of energy transfer by waves. In anisotropic mediums (in crystals, in plasma, in constant magnetic field) where the number of waves depends on frequency and direction of propagation, group velocity is defined as vector derivative Vg = dω/dk, and usually does not coincides in the direction with phase velocity. In mediums with strong absorption instead of group velocity, the value characterizing the velocity of energy transfer Ven = <S> / <W>, where <S> is the average energy flux density, and <W> is the average density of energy in waves, is introduced. In transparent mediums, Ven and Vg values coincide. According to the relativity theory, group velocity cannot exceed the velocity of propagation of light in vacuum [57–60].
2.10. PHOTONIC CRYSTALS
Much attention is paid to photonic crystals (PC), the structures where dielectric permittivity is modulated with the period, comparable with the wavelength of light [61]. Bragg diffraction of intrinsic electromagnetic conditions of Bloch[5] type on the border of Brillouin zone[6] of such structures leads to emergence of photonic band gap for radiation [62, 63].
Does it sound difficult? Let us try to simplify and reformulate.
PCs are the structures consisting of periodically alternating materials (fig. 18) when passing EMI through which Bragg diffraction arises (fig. 17) on periodically alternating borders of layers with different dielectric permittivity. This periodicity, by analogy with electronic zonal structure in regular crystal lattice, causes emergence of "photonic band gap", i. e., spectral area within which propagation of light is suppressed in all or in some chosen directions of PC.
When scales of modulation of dielectric permittivity and wavelength of probing radiation coincide, transmission spectrums contain the characteristic bands caused by Bragg reflection of electromagnetic waves. Manifestation of photonic properties is also met in wildlife (fig. 19). The irisation phenomenon, characteristic for PC (iridescent play of light) is observed in some butterflies (Vanessa kershawi, Morpho rhetenor), sea worm (Genus aphrodita) and in some other types of organisms [65].
Opal is one of the gemstones demonstrating PC properties. This mineral is characterized in various play of light, i. e., opalescence[7], and represents silicon dioxide hydrogel SiO2∙nH2O with variable water content and has the following chemical composition,% wt.: SiO2 – 65–90, H2O – 4.5–20, Al2O3 – up to 9, Fe2O3 – up to 3, TiO2 – up to 5. Sometimes opals have NiO, MnO2 impurities, organic substance. Opals can be colorless or have different colors due to impurities. Their refractive index is 1.44–1.46.
By means of electronic microscopy it was established that jeweler’s opals consist of spherical particles, homogeneous by the size, α-SiO2 (fig. 20) with a diameter of 150–450 nm which, in turn, are formed of smaller globular structures with a diameter of 5–50 nm. Voids of spheres packaging α-SiO2 are filled with amorphous silicon dioxide. Intensity of diffracted light is defined by "ideality" of microspheres packaging and distinction in refractive indices of crystal and amorphous silicon dioxide. The most noticeable irisation is observed for black opals, where distinction in refractive indices makes ~0.02.
PCs are of interest both to basic researches, and to different applications: in optical interconnection, laser technologies, for creation of essentially new appliances and devices. For example, it is possible to create new devices for control of luminous fluxes. Possibilities of management of group and phase velocity of light pulses, and also increase in efficiency of nonlinear and optical processes in such structures cause perspectives of PCs use in telecommunication systems (light filters, miniature wave guides, wavelength converters) [65].
Coverings and paints based on colloid microspheres are widely used. When they dry up, the film is formed opalescent in the sun at change of light incidence angle (especially popular for automotive industry).
It is considered that in the near future photons can already "replace" electrons not only in the information transfer systems, but also in computers (projects on creation of optical computer are under development) that will lead to revolutionary changes in all information technology. Use of PCs in designing of telecommunication systems can promote decrease in attenuation coefficient of optical fibers, creation of low-threshold laser radiators (visible and near Infrared ranges) and superfast optical switches of information flows.
From the point of view of achievement of required photon properties, synthetic opal-based nanocomposites filled with semiconductor materials are very perspective. It is caused both by low cost and technological effectiveness of preparation of relatively perfect opals and opal-based composites with thickness over 100 and even 1000 structural cells, and possibility of variation of their optical properties.
2.11. BIREFRINGENCE. KERR EFFECT
Birefringence is the effect of splitting in anisotropic mediums of ray of light into two components. For the first time the effect was found on crystal of Icelandic spar. If the ray of light is incident perpendicularly to crystal surface (fig. 21), it is split into two beams. The first beam continues to propagate directly and is called ordinary (o - ordinary), the second deviates and is called extraordinary (e - as extraordinary). As a result, two waves having mutually perpendicular linear polarization and diverging with different velocitys (respectively, with different indices of refraction) occur in the crystal.
The difference of refractive indices of two formed waves is used to characterize birefringence: Δn = no – ne. On the exit from crystal phase shift occurs due to different velocity.
Kerr effect is the emergence of birefringence in optically isotropic substances (liquids, glasses, crystals with the center of symmetry) under the influence of constant electric field. The isotropic substance placed in electric field becomes anisotropic, gaining properties of uniaxial crystal. Birefringence value Δn is proportional to square of electric field intensity E: Δn = nkE2, where n is refractive index of substance in lack of field, k is Kerr constant.
2.12. GOOS-HДNCHEN EFFECT
Goos-Hдnchen (GH) effect represents longitudinal shift of reflected beam in the conditions of total internal reflection relative to location determined by ray optics (fig. 22). This effect was discovered in 1943 by F. Goos and H. Hдnchen for multibeam interference in a glass plate. The observed shift was 1–2 λ at the wavelength of 578 nm.
One of the approaches to GH shift explanation was suggested in work [66]. With total internal reflection on dielectric surface, there is exponential attenuating evanescent field (see section 2.5). The energy flow through the plane, perpendicular to the plane of beam incidence and interface of two mediums, is not equal to zero, and the intensity of the incident and reflected beams are identical. In this case the law of energy conservation is true only in case of shift of reflected beam.
There are a number of publications [67–74] where the authors argue on negative GH shift. The majority of these works is theoretical, i. e. authors model negative GH shift in different mediums (absorbing mediums, Me surfaces) and under different incidence angles. Experimental confirmation of negative GH shift would prove the existence of NIM. And now M. Merano et al. [73] declare experimental confirmation of existence of negative GH shift in under conditions of reflection from gold film. However, surprisingly, the values of negative shift Dp (shift for p-polarized light) and positive shift Ds (for s-polarized light) are not specified in the text of article. Instead the difference Dp – Ds is given becoming negative with significant incidence angles (laser beam slides on gold film surface). One can only guess why the authors have presented experimental data in such form and what they have obtained in reality. Whether negative shift was recorded or simply shift Ds exceeded shift Dp? Experimental data in work [74] where the difference ΔTM – ΔTE is analyzed (TM is p-polarized light, and TE is s-polarized light) are similarly presented.
It should be noted that nowadays the researchers have not managed to confirm the existence of negative GH shift experimentally.
The list of the most interesting optical effects concerning EMI passing through substance can be continued. For example:
• parametrical dispersion of light – inelastic dispersion of light in homogeneous nonlinear medium where the parameters are modulated by light wave;
• Mandelstam-Brillouin dispersion – the dispersion of light on adiabatic fluctuations of density of condensed mediums which is followed by frequency change;
• Tyndall dispersion – elastic dispersion of light by non-uniform mediums;
• multiphoton absorption – interaction of EMI with substance where several photons are absorbed in one elementary act.
But these should be the subjects of other publications.
CONCLUSION
The first part of the overview concerned the NIMs and their critical analysis. Actually observed complex optical effects were briefly described in the second and third parts. Analyzing the material stated in the first part of article, it is possible to draw conclusion that NIM operating in the visible range and corresponding to Veselago and Pendry assumptions/predictions will not be created.
Modern researchers need to learn to distinguish the real-life complex, unusual phenomena (effects) from the foggy assumptions and hypotheses based, first of all, on ambitions of their authors. It is a very thin edge demanding the researchers to possess profound knowledge in subject domain, intuition in critical analysis of any new information and at the same time flexible thinking and ability to perceive new information, positively reacting to criticism.
One of the main directions of development of modern nanotechnologies is based on use of unique properties of the spatially arranged nanostructures and creation of optical analogs of elements of microelectronics on their base (conductors, diodes, transistors, memory elements, etc.). Such researches have ultimate goal to develop element base for creation of quantum computers and neural networks. And though the current level of development of technologies is still very far from direct implementation of such projects, it is possible to note undoubted importance of this area for creation of qualitatively new computing systems.
As for researches on creation of different composition materials, they, undoubtedly, will yield practical result [75–89]. For example, composites with nanoparticles (nanotubes, nanofibres) or submicronic particles are applied in Stealth technology, for creation of thermophotoelectric cells, photodetectors (sensors), for radiation cooling/heating of optoelectronic devices, in spectroscopy of huge Raman scattering, for manufacturing LC devices.
Imperceptibly for most of the readers, the researchers have shifted from the area of practical physics into the area of abstract mathematics. Therefore, the criticism concerning predictions for existence of metamaterials in the field of visible light remained almost unnoticed because of a large number of theoretical works in favor of such possibility.
[5] Bloch wave is a wave function of the particle moving in periodically non-uniform medium (crystal).
[6] Brillouin zones are the ranges of values of wave vector k, where energy of electrons changes continuously, and discontinues on the borders.
The wave vector k is one of the main characteristics of electron condition in a solid body. According to the band theory, the electron in crystal cannot have ionization continuum of values of energy, therefore the dependence of energy of electrons E(k) should not have sites corresponding to band gaps, i. e. curve E(k) should have discontinuities in some points.
The physical sense of the Brillouin zone borders is that they show such values of wave vectors or electron quasi-momentums where the electronic wave cannot propagate in a solid body [64].
[7] Ability of a mineral to emit multi-colored highlight from its surface (iridescence, iridescent change of colors). The effect is caused by the interferential phenomena connected with the regular structure of mineral, corresponding to lengths of waves of visible light by scale of frequency.
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