The theory of electromagnetically induced transparency (EIT) in a nonlinear conductive medium, which utilizes the classical approach instead of the traditional quantum optics scheme, has been recently suggested. We present the results of the bichromatic parametric irradiation experiments which validate the EIT effect within the mid-infrared spectrum. The studied materials include a highly dispersive gold (Au) and a low dispersive semiconductor zinc telluride (ZnTe). When the irradiation parameters satisfy the requirements of the EIT theory, the effect was shown to be strongly pronounced in both Au and ZnTe despite the very different optical properties of these conductors. The predictions of the theory regarding the existence of the EIT effect are shown to be in agreement with the experiment.
The effect of electromagnetically induced transparency (EIT) in non-Ohmic conductors, based on the concepts of classical nonlinear optics has been studied theoretically. We report an experimental demonstration of this effect within the mid-IR wavelength range. A low-dispersion semiconductor, i.e. ZnTe, and a highly dispersive gold film were subjected to bichromatic parametric irradiation and when specific phase matching conditions are satisfied, experimental evidence for a strong signature of EIT was found.
Homogeneous negative refractive index materials are introduced as an alternative to normally utilized inhomogeneous metamaterials. The theory of such materials was developed several years ago (A. Kussow and A. Akyurtlu, PRB 78, 205202 (2008)), and the effect is due to the coexistence of the spin-wave mode with the plasmonic mode, and both modes are activated by the electromagnetic field with simultaneous negative permittivity and permeability responses within the narrow frequency band close to the ferromagnetic resonance. To justify this theory, the thin films of ferromagnetic semiconductor, Cr-doped indium oxide, were fabricated, with clearly measured ferromagnetism at high saturation magnetization and a Curie temperature which is much higher than room temperature. The refractive index, within mid-IR, was extracted from combined transmittance and reflectance data and was compared with theoretical prediction. Also, a direct standard beam displacement method validates the effect of negative refraction in this material.
A mechanism based on two-wave mixing to dramatically reduce optical losses in non-ohmic conductors is proposed. The
losses in the probe mode are compensated due to the flow of energy from the support mode. The effect is derived from
the solution of non-linear Maxwell’s equations combined with coherence conditions for two parametrically coupled
waves. We provide a case which shows that this scheme can be realized experimentally in bulk semiconductors, e.g. zinc
telluride (ZnTe), within the mid-IR frequency range.
In this work, we show that natural crystals, or magnetic semiconductor, Cr-doped indium oxide, has a
negative refractive index at ~ 27.8 micron wavelength. The effect was predicted by two of us a few years
ago (A.G. Kussow and A. Akyurtlu, Phys. Rev. B, 78, 205202 (2008)). Our result seriously undermines
wide-spread opinion that only composite artificial metamaterials can demonstrate negative refractive index.
Thin ferromagnetic films of ICO were fabricated by original post-annealing sputtering method. FTIR R and
T measurements were processed to extract refractive index within the range of interest. The extracted from
combined transmittance and reflectance FTIR data negative refractive index band parameters are found to
be close to expected one.
If two parametrically-coupled fields, with the frequency of the probe p wave twice the frequency of the support s wave, are applied to a metal plasma, the non-linearity of the Boltzmann equation affects the permittivity. Based on the solution of the Boltzmann equation for the bichromatic problem, an analytical expression for the permittivity was derived. The amplitudes and the relative phase of the p and s waves can be adjusted to suppress the dielectric loss to almost zero within a narrow frequency band. If this frequency band overlaps with a negative-refractive-index band of a composite metamaterial, which contains a metallic component, the optical losses can be reduced by a factor of ∼ 30, with a figure of merit exceeding 100. An isotropic metamaterial comprising spherical Au and SiC nanoparticles can show that effect.
Novel mechanism of suppression losses in plasmonic subsystem in metals and semiconductors is suggested. If two
parametrically coupled fields are applied to a metal plasma, a non-linearity of the transport equation affects the electric
response, or the permittivity. If the coupling constant between the probe wave and the support wave is small, the
permittivity, at the frequency of the probe wave, is still Drude-like, with the re-normalized plasmon frequency. In the
case of a strong coupling, unusual response effects are possible (the induced transparency and the considerable
suppression of the plasmon losses), with profoundly non-Drude permittivity function.
The existing Quantum Optics- based models of negative refractive index in <i>atomic-vapor</i> medium (e.g. Ne,
Na) require unrealistically strong magnetic response of atoms combined with high atomic density. In
contrast to these gas-based models, our approach explores <i>solid-state</i> n-type semiconductor with well-defined
hydrogen-like donor atomic states within the band gap. Based on methods of Quantum Optics, we
have found that optically transparent indium oxide is negative refractive index material if doped with tin
and zinc <i>(In<sub>2-x</sub> Sn<sub>x/2</sub> Zn<sub>x/2</sub> O<sub>3</sub></i> (zinc-doped ITO)). The desirable negative refractive index effect is due to
coherent coupling an electric dipole transition with magnetic transition with proper detunings of the probe
and support laser beams (A.-G. Kussow and A. Akyurtlu, Int. J. Mod. Physics (2010)). The calculations
demonstrate the feasibility of the effect at ~ 10 THz with extremely high figure of merit FOM >> 10.
We examined materials which are homogeneous and which posses a negative index of refraction in (10-100) THz frequency range based on the following two ideas. Firstly, there are materials such as magnetic semiconductors (e.g. In2-xCrxO3,), and 3D transition metals (Fe, Ni), in which the high-frequency spin wave modes coexist with the plasmonic modes. Consequently, the spin wave mode, along with the plasmonic mode, are activated by the electromagnetic field of the light, with simultaneous negative permittivity and permeability responses at the edge of the Brillouin zone of the magnon spectra. This permeability response is weakly space-dispersive and anisotropic in the case of a single crystal, and is fully isotropic in a polycrystal with a small grain size. As a result, the polycrystalline material exhibits the negative refractive index effect within the narrow frequency band close to the ferromagnetic resonance. Secondly, based on methods of quantum optics, we investigated the possibility of achieving the negative index of refraction in a doped semiconductor. The quantum states of a hydrogen-like donor atom and states of an electron in the conduction band constitute a discrete-level atomic medium, and the coupling of an electric dipole transition with a magnetic dipole transition leads to coherent permeability and permittivity responses which results in the negative index effect. This scheme was implemented with tin-zinc-doped indium oxide, In2-xSnxO3 :Zn, and calculations show feasibility of this effect with a figure of merit (FOM) greater than 10.
We introduce a family of materials which are homogeneous and which posses a negative index of
refraction at optical frequencies. The desirable negative effect is not based on the chirality of the molecules,
but rather on two other ideas (A.-G. Kussow and A. Akyurtlu, Phys. Rev. B, 78, 205202 (2008)):
Firstly, there are known materials such as magnetic semiconductors (e.g. <i>In<sub>2-x</sub>Cr<sub>x</sub>O<sub>3</sub></i>,), and 3 d <i>transition
metals</i> (Fe, Ni), in which the high-frequency spin wave modes coexist with the plasmonic modes. The spin
wave (magnon) mode is coupled with the e.m. field of the light close to the boundary of the Brillouin zone.
Consequently, the spin wave mode, along with the plasmonic mode, are activated by the e.m. field of the
light, with simultaneous negative permittivity and permeability responses. As a result, the material exhibits
the negative refractive index effect within the frequency band close to the ferromagnetic resonance.
Secondly, based on methods of <i>Quantum Optics</i>, we discuss the possibility of achieving the negative index
of refraction in an <i>n-type doped semiconductor</i>. The quantum states of hydrogen-like donor atom and
states of an electron in conduction band constitute a discrete-level atomic medium within the optical range.
The coherent coupling of an electric dipole transition with a magnetic dipole transition leads to negative
permeability and permittivity responses and ensures the negative refractive index effect. The implementation
of this scheme is carried out in tin-doped indium oxide, <i>In<sub>2-x</sub>Sn<sub>x</sub>O<sub>3</sub></i> (ITO), and calculations show
feasibility of this effect with FOM > 10.