High-sensitivity and high-speed measurements of ultrashort pulses as short as 74 fs at 1.9 µm using a GRENOUILLE device.

Ultrashort laser pulse sources in the wavelength range of 1.8 to 2 µm have many potential applications including medicine, materials processing, and sensing. In the use of such lasers, a crucial task is to measure their pulse's temporal intensity and phase.

Femtosecond Er-Doped All-Fiber Laser with High-Density Well-Aligned Carbon-Nanotube-Based Thin-Film Saturable Absorber.

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.

Distributed Acoustic Sensor Using a Double Sagnac Interferometer Based on Wavelength Division Multiplexing.

We demonstrated a fiber optic distributed acoustic sensor based on a double Sagnac interferometer, using two wavelengths separated by CWDM modules. A mathematical model of signal formation principle, based on a shift in two signals analysis, was described and substantiated mathematically. The dependence of the sensor sensitivity on a disturbance coordinate and frequency was found and simulated, and helped determine a low sensitivity zone length and provided sensor scheme optimization.

Far-infrared and terahertz emitting diodes based on graphene/black-P and graphene/MoS heterostructures.

We propose the far-infrared and terahertz emitting diodes (FIR-EDs and THz-EDs) based on the graphene-layer/black phosphorus (GL/b-P) and graphene-layer/MoS (GL/MoS) heterostructures with the lateral hole and vertical electron injection and develop their device models. In these EDs, the GL serves as an active region emitting the FIR and THz photons. Depending on the material of the electron injector, the carriers in the GL can be either cooled or heated dictated by the interplay of the vertical electron injection and optical phonon recombination.

High-efficiency continuous-wave single-mode room-temperature operation of Cr:CdSe single-crystal laser with output power of 2.3 W.

We report on the study of quenching and thermal lensing based on simple effective lens approximation in a Cr:CdSe active medium, including detailed research on the medium's luminescence lifetime dependence on temperature in the 236-391 K range. This work has allowed us to partially overcome the limitations associated with thermal effects in the medium and build a laser system that allowed power scalability to be realized for the Cr:CdSe laser. Longitudinal pumping using a continuous-wave Tm-doped fiber laser at 1.

Terahertz spectroscopy of gelatin-embedded human brain gliomas of different grades: a road toward intraoperative THz diagnosis.

We applied terahertz (THz)-pulsed spectroscopy to study ex vivo the refractive index and absorption coefficient of human brain gliomas featuring different grades, as well as perifocal regions containing both intact and edematous tissues. Glioma samples from 26 patients were considered and analyzed according to further histological examination. In order to fix tissues for the THz measurements, we applied gelatin embedding, which allows for sustaining their THz response unaltered, as compared to that of the freshly excised tissues.

Wide-aperture aspherical lens for high-resolution terahertz imaging.

In this paper, we introduce wide-aperture aspherical lens for high-resolution terahertz (THz) imaging. The lens has been designed and analyzed by numerical methods of geometrical optics and electrodynamics. It has been made of high-density polyethylene by shaping at computer-controlled lathe and characterized using a continuous-wave THz imaging setup based on a backward-wave oscillator and Golay detector.

Note: Gaussian mixture model for event recognition in optical time-domain reflectometry based sensing systems.

We propose a novel approach to the recognition of particular classes of non-conventional events in signals from phase-sensitive optical time-domain-reflectometry-based sensors. Our algorithmic solution has two main features: filtering aimed at the de-nosing of signals and a Gaussian mixture model to cluster them. We test the proposed algorithm using experimentally measured signals.

Stable Similariton Generation in an All-Fiber Hybrid Mode-Locked Ring Laser for Frequency Metrology.

Ultrashort pulse lasers constitute an important tool in the emerging field of optical frequency metrology and are enabling unprecedented measurement capabilities and new applications in a wide range of fields, including precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. We demonstrate the generation of stable 127-fs self-similar pulses at a central wavelength of 1560 nm with 7.14-mW average output power.

High-energy, sub-100 fs, all-fiber stretched-pulse mode-locked Er-doped ring laser with a highly-nonlinear resonator.

We report on ultra-short stretched pulse generation in an all-fiber erbium-doped ring laser with a highly-nonlinear germanosilicate fiber inside the resonator with a slightly positive net-cavity group velocity dispersion (GVD). Stable 84 fs pulses were obtained with a 12 MHz repetition rate at a central wavelength of 1560 nm with a 48.1 nm spectral pulse width (full width at half maximum, FWHM) and 30 mW average output power; this corresponds to the 29.

A hybrid continuous-wave terahertz imaging system.

A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object.

Note: Improved technique for ultrashort lasers pulse width stabilization.

We have developed an improved pulse width stabilization method based on the second harmonic generation (SHG) technique using the relationship between pulse width, input intensity, and SHG intensity. On the basis of an analysis of the improved method accuracy, we then proposed a novel processing algorithm, which allowed us to increase the accuracy of pulse width stabilization to 1.2%.

[Hygienic principles of physical load standardizing in physical education of school children].

The paper outlines the hygienic principles of standardizing exercises in schoolchildren's physical training. Proceeding from the optimal (proper) daily body's energy requirements, including organized physical activities, the authors propose a method of their determination. The proper values of daily energy requirements are defined from their ratio to rated maximum values by the maximum oxygen consumption.

[Hygienic substantiation of physical load standards in physical education of schoolchildren].

The research specific to the changes in body functioning under the effect of various loads of cyclic character was carried out. The results thus obtained made it possible to analyze sex- and age-specific characteristics of body functional capacities of schoolchildren aged 6-15 (yearly characteristics). It was pointed out that by 13-14 years the schoolchildren, primarily girls, lost some of their adaptation capacity to physical load.