Polarization dynamics, stability and tunability of a dual-comb polarization-multiplexing ring-cavity fiber laser

In this paper, we present a polarization-multiplexed system capable of generating two stable optical frequency combs with tunable frequency differences in the range from 100 to 250 Hz and an extinction ratio of 16.5 dBm. Also, the polarization dynamics of a dual-frequency comb generated from a single mode-locked Er-doped fiber laser are experimentally studied. The obtained results will extend the application to areas such as polarization spectroscopy and dual-comb-based polarimetry

The light-oxygen effect in biological cells enhanced by highly localized surface plasmon-polaritons

Here at the first time we suggested that the surface plasmon-polariton phenomenon which it is well described in metallic nanostructures could also be used for explanation of the unexpectedly strong oxidative effects of the low-intensity laser irradiation in living matters (cells, tissues, organism). We demonstrated that the narrow-band laser emitting at 1265 nm could generate significant amount of the reactive oxygen species (ROS) in both HCT116 and CHO-K1 cell cultures. Such cellular ROS effects could be explained through the generation of highly localized plasmon-polaritons on the surface of mitochondrial crista. Our experimental conditions, the low-intensity irradiation, the narrow spectrum band (<4 nm) of the laser and comparably small size bio-structures (~10 μm) were shown to be sufficient for the plasmon-polariton generation and strong laser field confinement enabling the oxidative stress observed

Effects of high and low level 1265 nm laser irradiation on HCT116 cancer cells

The mechanism responsible for the oxidative stress due to photobiomodulation induced by 1265 nm laser is still unclear. Mitochondria are assumed to be the most probable acceptors of the 1265 nm laser irradiation. We study oxidative stress, mitochondrial potential, GSH, cell viability, DNA damage. We demonstrated that narrowband (highcoherent) and wideband lasers employed at the doses of 9.45 and 66.6-400 J/cm2, respectively, induce a dose-dependent cell death, increase ROS level, disturb mitochondrial functioning and can damage DNA. Thus, the 1265 nm lasers can affect the HCT116 cells through mitochondrial damage. Energy density increase contributes to cell damaging without heating effects

Ultra-short laser pulses propagation through mouse head tissues: experimental and computational study

We present a prototype and verification of a multichannel laser system applicable to optogenetic research. In vivo photostimulation of neural cells expressing photoconvertible phytochromes or opsins requires enough light irradiation delivery to the brain that cannot be supported by continues-wave (CW) light sources. The use of ultra-short pulsed (USP) lasers operating in the second near-infrared region (II-NIR) and allowing nonlinear activation and deactivation of the photoactuators is a promising method that allows to increase the penetration depth and provide spatio-temporal localisation of radiation in tissues. This study aimed to investigate the efficiency of USP light propagation in the skin, skull, and brain of the mouse head, as well as to compare it with the corresponding CW radiation propagation in the 750–830 nm and 1086–1183 nm wavelength ranges. The experimental results and computer modelling demonstrate that about 10–12% of the initial laser radiation can reach the brain tissues. These results prove that under certain conditions, the USP laser radiation can reach a penetration depth with required power that will be sufficient for non-linear activation of opsins/phytochromes in the brain of living animals

Comparison of nonlinear properties of monomer and dimer of bacterial phytochrome from Deinococcus radiodurans

Current medicine might be greatly enhanced by the ability to in vivo control and monitor neurons using opsins/phytochromes expressed in neural cells. The fundamental challenge with non-invasive neural cell activity regulation is a high absorption of visible light into biological tissues. This drawback could be mitigated by the photoconversion of phytochromes in spectral ranges with higher tissue transparency. In this study, we first demonstrated two-photon Pr-Pfr conversion of monomeric phytochrome at 1.2 µm wavelength. We did a comparison of linear and nonlinear conversion of truncated DrBphP bacterial phytochromes. This work provides a structured understanding of the optical properties of the dimer and monomer of phytochrome as well as their potential for use in optogenetics

High-Peak Power Frequency Modulation Pulse Generation in Cascaded Fiber Configurations with Inscribed Fiber Bragg Grating Arrays

We explored the dynamics of frequency-modulated (FM) pulses in a cascaded fiber configuration comprising one active and one passive optical fiber with multiple fiber Bragg gratings (FBGs) of different periods inscribed over the fiber configuration length. We present a theoretical formalism to describe the mechanisms of the FM pulse amplification and pulse compression in such fiber cascades resulting in peak powers up to ~0.7 MW. In combination with the decreasing dispersion fibers, the considered cascade configuration enables pico- and sub-picosecond pulse trains with a sub-terahertz repetition rate and sub-kW peak power generated directly from the continuous optical signal

High-Peak Power Frequency Modulation Pulse Generation in Cascaded Fiber Configurations with Inscribed Fiber Bragg Grating Arrays

We explored the dynamics of frequency-modulated (FM) pulses in a cascaded fiber configuration comprising one active and one passive optical fiber with multiple fiber Bragg gratings (FBGs) of different periods inscribed over the fiber configuration length. We present a theoretical formalism to describe the mechanisms of the FM pulse amplification and pulse compression in such fiber cascades resulting in peak powers up to ~0.7 MW. In combination with the decreasing dispersion fibers, the considered cascade configuration enables pico- and sub-picosecond pulse trains with a sub-terahertz repetition rate and sub-kW peak power generated directly from the continuous optical signal

Evaluation of penetration depth of near-infrared irradiation generated by tunable ultra-short pulsed laser in ex vivo samples of mouse head

Optogenetic research has opened up the possibility to control neurons that will help detect and treat neurological diseases in the early stage. Treatment of dysfunctions requires exposure to a partial neural network accessible through the absorption of opsins or phytochromes expressed in the brain matter. The use of II-NIR USP lasers makes it possible to non-linear activate and deactivate photoactuators in neuronal cells through the skull. The possible obstacles for noninvasive stimulation are the limits in light penetration depth, scattering and absorption by biological tissues. This research aimed to investigate light propagation and penetration depth in skin, skull and brain matter of mouse head. To evaluate the light transmittance in brain tissues, we developed an experimental setup with a tunable ultra-short pulsed laser source operating at the wavelength range of 1.1-1.2 μm. This spectrum range corresponds to the spectra of nonlinear absorption of opsins/phytochromes and matches the second biological window where laser irradiation can penetrate the skin and skull bone without damaging and overheating them. The experimental results demonstrate that under certain conditions, the ultra-short pulsed laser radiation can reach a penetration depth with required power that will be sufficient for non-linear activation of opsins/phytochromes in the brain of living animals. These results could support applications of II-NIR USP laser in non-invasive optogenetics, photobiomodulation of the brain functioning and even neurological disorders diagnostics

Dissipative soliton breathing dynamics driven by desynchronization of orthogonal polarization states

Breathing solitons, i.e., dynamic dissipative solitons with oscillating pulse shape and energy caused by different mechanisms of spatiotemporal instabilities, have received considerable interest from the aspects of nonlinear science and potential applications. However, by far, the study of breathing solitons is still limited within the time scale of hundreds of cavity round trips, which ignores the slow dynamics. To fill this lacuna, we theoretically investigate a new type of vector dissipative soliton breathing regime and experimentally demonstrate this concept using mode-locked fiber lasers, which arise from the desynchronization of orthogonal states of polarization (SOPs) in the form of complex oscillations of the phase difference between the states. The dynamic evolution of polarization states of the vector breathings solitons takes the form of a trajectory connecting two quasi-equilibrium orthogonal SOPs on the surface of the Poincaré sphere. The dwelling time near each state is on the scale of a tenth of a thousand cavity round trip times that equals the breathing period, which is up to 2 orders of magnitude longer than that for common breathers. The obtained results can reveal concepts in nonlinear science and may unlock approaches to the flexible manipulation of laser waveforms toward various applications in spectroscopy and metrology