Dmitry A. Sidorov-Biryukov

Pressure control of phase matching in high-order harmonic generation in hollow fibers filled with an absorbing weakly ionizing gas

High-order harmonic generation in a hollow fiber filled with a weakly ionizing gas is theoretically analyzed within the framework of the slowly varying envelope approximation. The gas pressure that corresponds to maximum efficiency of frequency conversion, the absorption coefficient, the phase mismatch owing to gas dispersion, and the enhancement of harmonic-generation efficiency owing to waveguide phase matching are estimated for 27th-harmonic generation in hollow fibers filled with helium, neon, argon, krypton, or xenon. As a result of the ionization-induced self-phase modulation of the pump pulse in a hollow fiber filled with a weakly ionizing gas, the phase mismatch changes within the pump pulse, decreasing the overall efficiency of harmonic generation and making the harmonic-generation efficiency less sensitive to the gas pressure in the hollow fiber.

Soft-glass photonic-crystal fibers for frequency shifting and white-light spectral superbroadening of femtosecond Cr:forsterite laser pulses

Structural dispersion and nonlinearity management of multicomponent-glass photonic-crystal fibers is shown to allow wavelength-tunable frequency shifting and white-light spectral transformation of femtosecond Cr:forsterite laser pulses. Launching 200 fs pulses of 1.25 μm Cr:forsterite laser radiation into such dispersion-managed soft-glass photonic-crystal fibers in the regime of anomalous dispersion, we demonstrate spectrally tailored supercontinuum generation and frequency upshifting, yielding isolated spectral components with central wavelengths ranging from 400 to 900 nm.

Application of coherent four-wave mixing for two-dimensional mapping of the spatial distribution of excited atoms in a laser-produced plasma

Abstract An experimental technique for the two-dimensional mapping of the relative populations of excited states of atoms and ions in a low-temperature plasma of optical breakdown is developed on the basis of coherent four-wave mixing (FWM) with hyper-Raman resonances. The possibility to extract information concerning the spatial distribution of the populations of excited atomic and ionic states from two-dimensional maps of the FWM intensity allowing for phase mismatch and one-photon absorption is considered. Conditions when FWM in a plasma occurs in the phase-matched regime and is not subject to a considerable influence of one-photon absorption are experimentally determined.

Thermogenetic neurostimulation with single-cell resolution

Thermogenetics is a promising innovative neurostimulation technique, which enables robust activation of neurons using thermosensitive transient receptor potential (TRP) cation channels. Broader application of this approach in neuroscience is, however, hindered by a limited variety of suitable ion channels, and by low spatial and temporal resolution of neuronal activation when TRP channels are activated by ambient temperature variations or chemical agonists. Here, we demonstrate rapid, robust and reproducible repeated activation of snake TRPA1 channels heterologously expressed in non-neuronal cells, mouse neurons and zebrafish neurons in vivo by infrared (IR) laser radiation. A fibre-optic probe that integrates a nitrogen−vacancy (NV) diamond quantum sensor with optical and microwave waveguide delivery enables thermometry with single-cell resolution, allowing neurons to be activated by exceptionally mild heating, thus preventing the damaging effects of excessive heat. The neuronal responses to the activation by IR laser radiation are fully characterized using Ca2+ imaging and electrophysiology, providing, for the first time, a complete framework for a thermogenetic manipulation of individual neurons using IR light.

Light confinement and supercontinuum generation switching in photonic-molecule modes of a microstructure fiber

The modes guided in a ring system of microstructure-integrated fibers are shown to have much in common with electron wave functions in a two-dimensional polyatomic cyclic molecule. This photonic-molecule analogy provides, in particular, an illustrative and physically clear model of dispersion properties and the mode structure of an electromagnetic field in microstructure fibers of the considered type. A high degree of light confinement in waveguide modes of such a photonic molecule enhances nonlinear-optical processes, permitting an octave spectral broadening to be achieved for low-energy femtosecond laser pulses.

Hollow-Core-Waveguide Compression of 22-mJ 3.9-µm Pulses

We present post-compression of 22-mJ 90-fs pulses at 3.9 µm via spectralbroadening in a noble-gas-filled 1 mm core diameter 3 meter long capillary with over 60% throughput and recompressed in a bulk BaF2 plate down to 33 fs.

Multimodal nonlinear Raman microspectroscopy with ultrashort chirped laser pulses

We demonstrate the physical principles of multimodal nonlinear optical microspectroscopy, integrating methods of coherent and stimulated Raman scattering of ultrashort chirped laser pulses in a single optical scheme. Nonlinear phase distortions of ultrashort laser pulses are accurately compensated within a broad spectral range in this scheme to enable a high-spectral-resolution laser microspectroscopy that can reliably resolve groups of fingerprint molecular vibrations with close frequencies, thus facilitating an analysis of complex multicomponent systems.