E. V. Naumova

Study of the properties of artificial anisotropic structures with high chirality

The chiral properties of an artificial anisotropic structure composed of microhelices are numerically simulated using the example of a sample developed by a team of authors from the Institute of Semiconductor Physics of the Russian Academy of Sciences. It is shown that this artificial structure can exhibit strong chiral properties in the THz range. Analytical expressions for the dielectric, magnetic, and chiral susceptibilities of the structure are derived on the condition of strong gyrotropy. The calculated values of the angle of the electromagnetic-wave polarization plane rotation and the circular dichroism are compared with the experimental results.

Manufacturing chiral electromagnetic metamaterials by directional rolling of strained heterofilms

We show that THz chiral metamaterials consisting of large regular arrays of metal–semiconductor microhelices can be manufactured from strained heterofilms by directional rolling. We also report the results of an experimental study of the electromagnetic properties of such arrays.

Investigation of electromagnetic properties of a high absorptive, weakly reflective metamaterial—substrate system with compensated chirality

In the present paper, a theoretical and experimental study of a highly absorptive, weakly reflective coating designed and fabricated on the basis of 3D THz resonant elements is reported. Transmission and reflection of electromagnetic waves from the metamaterial-substrate structure involving a highly absorptive, weakly reflective array of artificial bi-anisotropic elements were analyzed. The samples contained paired right-handed and left-handed helices, due to the fact that the chirality was compensated. The parameters of helices were optimized to achieve roughly identical values of dielectric permittivity and magnetic permeability. As a result, the metamaterial exhibited weak reflectivity in the vicinity of resonance frequency. On the other hand, effective resonance properties of the helices were tuned to ensure substantial absorption of THz radiation. Analytical expressions for the coefficients of radiation reflection and transmission in the samples were derived by solving a boundary-value problem for th...

Terahertz-range chiral metamaterials based on helices made of metal-semiconductor nanofilms

Chiral metamaterials of the terahertz range are formed by means of rolling of strained nanofilms. Structural elements of these metamaterials are metal-semiconductor microhelices. Resonant optical activity of new metamaterials in the terahertz range is demonstrated. Arrays of model wire helices are formed and tested in the microwave range.

Polarization rotation of THz radiation by an array of helices.

Novel approach to controlling polarization of THz radiation is introduced. Polarization plane rotation of transmitted wave by a monolayer of precise microhelices was demonstrated by experiments on the Novosibirsk free electron laser. It had strongly resonant character. Modulation of polarization opens up new possibilities in communication, biomedical, chemistry, security, imaging and spectroscopy applications.

Investigation of the properties of weakly reflective metamaterials with compensated chirality

The properties of an artificial anisotropic structure formed by microhelices have been numerically simulated by the example of a specially designed sample. The sample contains paired helices with right- and left-handed twisting directions, due to which the metamaterial chirality is compensated for. Helices are characterized by precalculated optimal parameters; as a result, the permittivity and permeability of metamaterial are approximately equal. Therefore, the wave impedance of the structure is close to the impedance of free space in the frequency range near 2 THz and the reflection of normally incident electromagnetic waves is weak. A boundary problem is solved and an analytical expression is obtained for the reflection and transmission coefficients of an electromagnetic wave passing through the structure. The simulated properties of the structure are compared with experimental results.

High power THz applications on the NovoFEL

High power THz applications on the Novosibirsk terahertz free electron laser are described.

Terahertz optical activity and metamaterial properties of 2D array of metal-semiconductor microhelices

The terahertz optical activity of 2D arrays of metal-semiconductor microhelices was investigated by Fourier spectroscopy and free electron laser methods. We found strong resonance at first harmonic with wavelength twice helix length and weaker resonances at the second and third harmonics. The resonances are present in the transmittance, reflectance, and absorption spectra. For linear polarized radiation, a chirality of the media leads to their ellipticity at resonance frequency and rotation of the polarization plane in opposite directions (up to 16.5 degrees) on both sides of the resonance. It has been shown by direct interferometric method on free electron laser that the refraction index of the investigated layer has negative values for definite circular wave at certain frequencies. Its minimal value is −0.11.