Maxim M. Nazarov

Excitation and focusing of terahertz surface plasmons using a grating coupler with elliptically curved grooves

Using a diffraction grating with elliptically curved grooves engraved at the top of an aluminum slab, surface plasmons in the terahertz frequency range are efficiently excited with an incoming parallel beam and focused over the metal surface down to the diffraction limit. At 0.5 THz, the lateral confinement of the surface plasmon is 1 mm while its extension in air is 0.74 mm, much smaller than the calculated value for a semi-infinite substrate having the conductivity of bulk aluminum.

THz time-domain spectroscopy study of grating couplers and segmented grating filters

THz waves can be used to test devices scaled in the millimeter range before manufacturing micron-sized optical devices. We demonstrate this concept by studying diffraction grating structures by THz time-domain spectroscopy. We show that 1D silicon grid gratings behave as narrow band high reflectivity mirror for focused THz beams.

Characterization of Highly Doped Si Through the Excitation of THz Surface Plasmons

We excite surface plasmons (SPs) at the surface of highly doped Si using a prism coupler, and we study the propagation properties of these SPs in order to characterize the terahertz (THz) response of the doped semiconductor. Thanks to the long interaction length of the propagating SP with the substrate material, the method is more sensitive than classical THz time-domain spectroscopy in reflection or in transmission. Moreover, we propose a new technique based on measuring the SP signal, for which the delicate problem of accurately measuring the phase of the signal is solved. All of these different experiment techniques allow us to determine reliably the dielectric function of highly doped Si in the THz range. It appears that the experimentally determined values differ strongly from the ones calculated with a Drude model.

GaSe 1−x S x and GaSe 1−x Te x solid solutions for terahertz generation and detection

Dielectric properties of Bridgman grown GaSe single crystals as well as those of GaSe<inf>1−x</inf>S<inf>x</inf> and GaSe<inf>1−x</inf>Te<inf>x</inf> solid solution crystals have been measured by terahertz time-domain spectroscopy. Terahertz generation via optical rectification of femtosecond laser pulses and electro-optic detection in these crystals have been studied.

In-vitro terahertz spectroscopy of rat skin under the action of dehydrating agents

In the paper we present the results of study of rat skin and rat subcutaneous tumor under the action of dehydrating agents in terahertz (THz) range (15-30 THz). Frustrated Total Internal Reflection (FTIR) spectra were obtained with infrared Fourier spectrometer Nicolet 6700 and then they were recalculated in the transmittance spectra with Omnic software. Experiments were carried out with healthy and xenografted tumor in skin tissue in vitro. As the dehydrating agents 100% glycerol, 40%-water glucose solution, PEG-600, and propylene glycol were used. To determine the effect of the optical clearing agent (OCA), the alterations of terahertz transmittance for the samples were analyzed. The results have shown that PEG-600 and 40%-glucose water solution are the most effective dehydrating agent. The transmittance of healthy skin after PEG-600 application increased approximately by 6% and the transmittance of tumor tissue after PEG- 600 and 40%-glucose water solution application increased approximately by 8%. Obtained data can be useful for further application of terahertz radiation for tumor diagnostics.

Properties of aqueous solutions in THz frequency range

Terahertz time-domain spectroscopy has been used for measuring of bovine serum albumin and glucose solutions response. The transmission and the attenuated total internal reflection geometries have been combined for analyzing the dielectric properties of aqueous solutions spectra at 0.07-3.2 THz.

Terahertz applications of the materials made from nanostructured alumina oxyhydroxide (NOA), its modifications and composites

The properties of new porous materials made from nanostructured alumina oxyhydroxides (NAO) were studied in THz range. The effects observed with the raw, annealed, and chemically modified NOA have revealed properties allowing using such materials for various terahertz devices, particularly for a low loss holey waveguides. We also discuss the results of THz-TDS detection of adsorbed molecular layers at the NAO surface.

A flexible terahertz waveguide for delivery and filtering of quantum-cascade laser radiation

We demonstrate that a specially designed microstructured polymer waveguide can improve the quality of quantum cascade laser radiation. It can filter out undesired side frequencies and transform the delivered radiation to a sub-millimeter size beam with a Gaussian-like cross-section. The spatial distribution of the bended waveguide mode is measured, and low bending losses of the fundamental mode are confirmed. Detailed optimization of a capillary structure for 3u2009THz frequency allows delivering single frequency radiation up to a 1 meter distance. The results of the experimental study are confirmed by calculations with an accurate mode solver that explains the achieved losses of ∼10u2009dB/m. A further improvement strategy is suggested.We demonstrate that a specially designed microstructured polymer waveguide can improve the quality of quantum cascade laser radiation. It can filter out undesired side frequencies and transform the delivered radiation to a sub-millimeter size beam with a Gaussian-like cross-section. The spatial distribution of the bended waveguide mode is measured, and low bending losses of the fundamental mode are confirmed. Detailed optimization of a capillary structure for 3u2009THz frequency allows delivering single frequency radiation up to a 1 meter distance. The results of the experimental study are confirmed by calculations with an accurate mode solver that explains the achieved losses of ∼10u2009dB/m. A further improvement strategy is suggested.

Investigation of bovine serum albumin glycation by THz spectroscopy

Protein glycation is accelerated under hyperglycemic conditions resulting to loss in the structure and biological functions of proteins. The transmission THz spectroscopy has been used for measuring of bovine serum albumin glycation dynamics. It was found that amplitude of albumin THz absorption depends on type of sugars and incubation time.

THz emission from a femtosecond laser focus in a bicolor scheme in the ionization-free regime

The interaction between high intensity ultrashort laser pulses and the atomic gas in the ionization-free regime leads to the emission of coherent, short pulse radiation at terahertz frequency. In this work we discuss a model for this effect and its experimental realization.