Gleb M. Katyba

Band-gap nonlinear optical generation: The structure of internal optical field and the structural light focusing

A novel approach for the enhancement of nonlinear optical effects inside globular photonic crystals (PCs) is proposed and systematically studied via numerical simulations. The enhanced optical harmonic generation is associated with two- and three-dimensional PC pumping with the wavelength corresponding to different PC band-gaps. The interactions between light and the PC are numerically simulated using the finite-difference time-domain technique for solving the Maxwells equations. Both empty and infiltrated two-dimensional PC structures are considered. A significant enhancement of harmonic generation is predicted owing to the highly efficient PC pumping based on the structural light focusing effect inside the PC structure. It is shown that a highly efficient harmonic generation could be attained for both the empty and infiltrated two- and three-dimensional PCs. We are demonstrating the ability for two times enhancement of the parametric decay efficiency, one order enhancement of the second harmonic genera...

Terahertz Photonic Crystal Waveguides Based on Sapphire Shaped Crystals

In this paper, an ability for highly efficient terahertz (THz) waveguiding in multichannel sapphire shaped crystals is demonstrated. The edge-defined film-fed growth (EFG) technique (or Stepanov technique) of shaped crystal growth has been implemented to manufacture the THz photonic crystalline (PC) waveguide. The PC waveguide has been characterized using both numerical simulations and experimental study. It allows guiding the THz waves in multimode regime with the minimal dispersion in frequency range of 1.0-1.55 THz and the minimal power extinction coefficient of 0.02 dB/cm at 1.45 THz. The mode interference phenomenon has been observed in this waveguide highlighting the prospectives of its use for intrawaveguide interferometry. These results demonstrate the capabilities of combining the EFG/Stepanov technique advantages with unique properties of sapphire, such as relatively low THz-wave absorption, high mechanical, thermal, chemical, and radiation strength, for manufacturing the THz waveguides characterized with low loss and dispersion and suitable for use in wide range of THz technology applications in biomedical and material sciences, including sensing in aggressive environment.

Numerical simulation of terahertz-wave propagation in photonic crystal waveguide based on sapphire shaped crystal

Terahertz (THz) waveguiding in sapphire shaped single crystal has been studied using the numerical simulations. The numerical finite-difference analysis has been implemented to characterize the dispersion and loss in the photonic crystalline waveguide containing hollow cylindrical channels, which form the hexagonal lattice. Observed results demonstrate the ability to guide the THz-waves in multi-mode regime in wide frequency range with the minimal power extinction coefficient of 0.02 dB/cm at 1.45 THz. This shows the prospectives of the shaped crystals for highly-efficient THz waveguiding.

Parametric emission generation in cubic noncentrosymmetrical crystals

The physics of polariton radiation generation in cube noncentrosymmetrical crystals is discussed. Theoretical values of polariton radiation frequencies in GaP, ZnSe, ZnTe and GaAs crystals were found. The basic circuit of parametrical terahertz radiation generator is introduced.

A potential of terahertz solid immersion microscopy for visualizing sub-wavelength-scale tissue spheroids

We have developed a method of the terahertz (THz) solid immersion microscopy for the reflection-mode imaging of soft biological tissues. It relies on the use of the solid immersion lens (SIL), which employs the electromagnetic wave focusing into the evanescent-field volume (i.e. at a small distance behind the medium possessing high refractive index) and yields reduction in the dimensions of the THz beam caustic. We have assembled an experimental setup using a backward-wave oscillator, as a source of the continuous-wave THz radiation featuring λ= 500 μm, a Golay cell, as a detector of the THz wave intensity, and a THz SIL comprised of a wide-aperture aspherical singlet, a truncated sphere and a thin scanning windows. The truncated sphere and the scanning window are made of high-resistivity float-zone silicon and form a unitary optical element mounted in front of the object plane for the resolution enhancement. The truncated sphere is rigidly fixed, while the scanning window moves in lateral directions, allowing for handling and visualizing the soft tissues. We have applied the experimental setup for imaging of a razor blade to demonstrate the advanced 0:2λ resolution of the proposed imaging arrangement. Finally, we have performed imaging of sub-wavelength-scale tissue spheroids to highlight potential of the THz solid immersion microscopy in biology and medicine.

In vitro terahertz spectroscopy of gelatin-embedded human brain tumors: a pilot study

We have performed the in vitro terahertz (THz) spectroscopy of human brain tumors. In order to fix tissues for the THz measurements, we have applied the gelatin embedding. It allows for preserving tissues from hydration/dehydration and sustaining their THz response similar to that of the freshly-excised tissues for a long time after resection. We have assembled an experimental setup for the reflection-mode measurements of human brain tissues based on the THz pulsed spectrometer. We have used this setup to study in vitro the refractive index and the amplitude absorption coefficient of 2 samples of malignant glioma (grade IV), 1 sample of meningioma (grade I), and samples of intact tissues. We have observed significant differences between the THz responses of normal and pathological tissues of the brain. The results of this paper highlight the potential of the THz technology in the intraoperative neurodiagnosis of tumors relying on the endogenous labels of tumorous tissues.

Sapphire shaped crystals for laser-assisted cryodestruction of biological tissues

We have developed cryo-applicators based on the sapphire shaped crystals fabricated using the edge-defined film-fed growth (EFG) and noncapillary shaping (NCS) techniques. Due to the unique physical properties of sapphire: i.e. high thermal, mechanical, and chemical strength, impressive thermal conductivity and optical transparency, these cryo-applicators yield combination of the tissue cryo-destruction with its exposure to laser radiation for controlling the thermal regimes of cryosurgery, and with the optical diagnosis of tissue freezing. We have applied the proposed sapphire cryo-applicators for the destruction of tissues in vitro. The observed results highlight the prospectives of the sapphire cryo-applicators in cryosurgery.

Technological aspects of manufacturing terahertz photonic crystal waveguides based on sapphire shaped crystals

Recently, terahertz (THz) photonic crystal waveguides based on sapphire shaped crystals have been proposed. These waveguides combine unique properties of sapphire with advantages of the edge-defined film-fed growth (EFG) or Stepanov technique of shaped crystal growth and allow guiding THz waves in a wide spectral range with small dispersion and losses. The sapphire photonic crystal waveguides are capable for operation in aggressive environment, which makes possible to perform high-temperature and high-pressure THz measurements, as well as THz measurements of aggressive chemicals. In this paper, the technological aspects of sapphire THz photonic crystal waveguide manufacturing by the EFG/Stepanov technique (including, the problems of seeding and automated control of multichannel shaped crystal growth) have been described. Prospective applications of sapphire photonic crystal waveguides in various branches of THz science and technology have been discussed.

Terahertz waveguides based on multichannel sapphire shaped crystals

In this paper, an advantage of sapphire shaped crystal use for highly efficient terahertz (THz) waveguiding is discussed. The THz photonic crystal waveguide has been manufactured using the edge-defined film-fed growth (EFG) or Stepanov technique of shaped crystal growth. The effective mode index and extinction coefficient of the waveguide have been experimentally studied using the THz pulsed spectroscopy. The observed results have shown that the multichannel sapphire crystal allows guiding the THz waves with minimal dispersion in frequency range of 1:0 to 1:55 THz and minimal loss of 2 dB/m at 1:45 THz. The waveguides based on sapphire shaped crystals can be employed in wide range of THz technology applications, including non-destructive evaluation of materials, medical diagnostics, and sensing in aggressive environment.

Structural light focusing phenomenon and enhanced second harmonic generation in NaNO2-infiltrated opal photonic crystal

We report new experimental results on enhanced second harmonic generation using a structural light focusing phenomenon in photonic crystals (PCs). We use opal-based PC, infiltrated with NaNO2 and pumped with femtosecond laser pulses at various incidence angles, in order to examine the dependence of second harmonic generation efficiency on the pumping wavelength location toward the PC band-gap. We demonstrate one order enhancement of second harmonic generation in case of PC band-gap pumping in comparison to non-band- gap pumping. Second harmonic generation is performed in reflection mode with the maximum of generation in the direction of mirror reflection. We demonstrate that the spectrum of second harmonic does not narrow with the quasi-phase matching condition in case of band-gap generation, and second harmonic spectrum corresponding to non-band-gap generation undergoes 1.5 times narrowing due to the quasi-phase matching.