We present an experimental investigation of the amplification of soliton molecules (SM) in an erbium-doped all-fiber amplifier. The amplification of a 10-pulse regime (with 509 fs pulse duration, 2.64 ps pulses separation, and low repetition rate Allan deviation of 1.98 & sdot;10-9 at a 1 s averaging interval of 10-hour free-running measurement), generated by an erbium-doped fiber ring laser mode-locked through nonlinear polarization evolution (NPE), achieved an average power of 152 mW for stable amplified soliton molecules (SM). This process resulted in high coupling states with the same number of pulses and spectrum broadening leading to coherent super-continuum generation. A wide spectrum with a comb-teeth structure in the range [1400 nm-1700 nm] was obtained without pulse fission (10 pulses remains coherently in time domain with increased pulse duration up to 1.129 ps and without changing in the time separation between pulses), achieved through precise amplification of the SM without the use of high-nonlinearity fibers (HNLFs), and with low relative intensity noise of 0.0108 % in the range of 10 kHz-1 MHz. Additionally, we demonstrate the characteristics of amplified SM as a function of the number of pulses, which was varied by adjusting the pump power of the master oscillator. The number of solitons remained constant during extra-cavity amplification; however, the results for SM amplification with 3, 4, 5, 7, 9, and 10 pulses indicate tunability in both the average and peak power of the amplified pulses. These findings position soliton molecules as a novel tool for optical frequency comb spectroscopy and with spectrum broadening suitable for potential application in f-2f interferometry.

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. Such measurement devices are most useful when they are simple to build and operate and also have high speed and high sensitivity. The GRENOUILLE measurement device with few components, no moving parts, sensitivity of hundreds of picojoules, and measurement speed of hundreds of milliseconds, is commonly used to solve this problem at other wavelengths. In this paper, the measurement of ultrashort pulses by a GRENOUILLE device, developed using a silicon matrix sensor, for pulses in the wavelength range of 1.8 to 2 µm has been demonstrated. It is shown that ultrashort pulses with durations of 74 to 900 fs and a maximum spectral FWHM of 85 nm can be measured with this device. The recently developed ultra-reliable RANA approach was used for pulse retrieval from the measured traces. The device's performance was validated by comparing its measurements with those obtained by the robust FROG technique.

An Er-doped all-fiber ultrashort pulse laser with positive total net-cavity group-velocity dispersion is demonstrated based on a hybrid mode-locking mechanism ensured by single-walled carbon–boron–nitrogen nanotubes with coaction of the nonlinear polarization evolution effect. The generation regime with a similariton-like spectrum is obtained. The spectrum width is ~31.5 nm, and the minimal pulse duration is ~294 fs at full width at half maximum. The average output power is ~3.2 mW, corresponding to 0.376 nJ pulse energy and 1.25 kW peak power. The fundamental pulse repetition rate is ~8.5 MHz, with a signal-to-noise ratio of 60 dB. The standard deviation of average output optical power stability, measured for 12 h, is about ~1% RMS, and the maximum level of relative intensity noise (RIN) does not exceed <−120 dBc/Hz in the 30 Hz–1 MHz frequency range. To prove the similariton-like regime generation, we also studied numerically and experimentally the pulse evolution during propagation through a laser resonator and output single-mode fiber with anomalous dispersion.

We report on the generation and amplification of soliton molecule regime in master oscillator fiber amplifier based on erbium-doped fiber laser. The amplification of 15 pulses regime with 432 fs pulses duration and 46 mW average power in 1m long erbium-doped fiber amplifier led to the generation of 20 pulses regime with 449 fs pulses duration and 102 mW average power.

Numerical study based on nonlinear Schrodinger equation was conducted to optimize the characteristics of all-fiber master oscillator fiber amplifier based on erbium-doped fiber laser. The generation of supercontinuum in high-nonlinearity fiber (HNLF) was achieved. The optimization of HNLF length, and the average power of amplified pulses led to 1155 nm spectral width at -20dB.

The effective launch of low-noise soliton molecules was obtained using newly developed partially-ordered densely packed single-walled carbon nanotubes in a hybrid scheme of an Er-doped ultrashort pulse fiber laser.

The self – assembly method was used to prepare aligned single - walled carbon nanotubes for application as a saturable absorber in ultrashort pulses lasers. The alignment of nanotubes was investigated by polarized Raman spectroscopy. Moreover, the nonlinear characteristics of the prepared aligned nanotubes film were compared to typical film with random nanotubes. The saturable absorber modulation depth has increased by 6% due to the alignment features.

A fiber laser generating noise-like two-pulse bunches with duration of $\sim 66 \ \mathrm{fs}$ is presented. The transformation of these pulses into a multi-bound soliton regime with a duration of 142 fs is investigated.

Purpose: This section reflects the level of influence of laser sources in reducing the harmful effects of various medical procedures, as well as in increasing their efficiency. Current trends of further reduction of the laser procedures invasiveness are analysed, and the method of reducing negative factors by decreasing the laser pulses duration is highlighted. Analysis of the adverse effects of laser treatment in medical operations and procedures: The key factors of intra- and postoperative damage in laser surgery and procedures in urology, dermatology, ophthalmology and dentistry are analysed. The magnitude of these factors when using currently clinically available laser equipment is reflected. Analysis of the possibility of reducing negative factors in subpicosecond and femtosecond laser operations and procedures: The dynamics of the same harmful factors and complications for similar medical procedures using subpicosecond and femtosecond laser radiation have been reviewed. A significant reduction in harmful factors and complications of their application is shown in comparison with the use of currently available medical laser systems. Conclusion: The basic data on harmful factors reduction in urology, dermatology, ophthalmology and dentistry using laser sources with subpicosecond and femtosecond pulses are presented. Prospects for the implementation of laser systems based on ultrashort duration sources in various fields of medicine are considered.

We report the production of a saturable absorber (SA) based on aligned single-walled carbon nanotubes SWCNTs by the self-assembly method. The ultrafast saturation behavior of prepared aligned and random nanostructures shows an increase of modulation depth by 6 % due to the alignment method. We also observed the dependence of aligned SWCNTs loss on the polarization direction of laser radiation. All-fiber Er-doped hybrid mode-locked fiber laser was demonstrated based on the aligned/random SWCNTs-based SAs. We achieved the generation of stable stretched pulses with a pulse duration of 490/569 fs and an average output power of 20.7/18.25 mW. We also investigated the advantages of using aligned SWCNTs compared to the typical structure with random tube distribution. We show that the use of aligned SWCNTs film increased the SNR by 24.5, decreased the mode-locking threshold power by 42 mW, and decreased the RIN level by (20-25) dB in the frequency range [similar to 0 Hz- 100 kHz] and similar to 8 dB in the range [100 kHz-1 MHz].

Accurate laser spot-size measurements are important in many scientific and industrial applications: the knife-edge technique is commonly used to measure the laser beam dimension due to the relative ease, low cost, and reliability of the measurement. We propose an original use of a numerical method to evaluate the standard uncertainty of the measured laser spot-size in knife-edge measurements and we apply it to the analysis of experimental data from two different laser sources. The method allows obtaining the sensitivities of the spot-size uncertainty to the uncertainties of relevant input quantities such as the measured optical power and the knife-edge displacement. Since the indirect measurement of laser spot-size by the knife-edge technique is non-linear, analytical calculation of the uncertainty sensitivities is not possible and they are evaluated numerically based on experimental data and specific input noise/uncertainty conditions. By our analysis, calculation of specific sensitivities for two different experimental conditions is done and then used to estimate the standard uncertainty of the measured parameter: the standard radius of a Gaussian-beam laser spot. More generally, the method proposed allows evaluating the effects of different uncertainty contributions on the laser spot-size uncertainty estimation. This can then suggest proper design of the measurement experiment with the goal of reducing the final uncertainty. Accurate measurements, and of known and tailorable accuracy, of the laser parameters are of interest in different industrial applications where precise beam shaping is important.

The work is devoted to the optimal wavelengths selection for the task of methane monitoring using an acousto-optical spectrometer installed on board a satellite. The results of mathematical modeling are given. It is shown that the spectral width of the instrumental function has a significant impact on the selection result, while the atmosphere model used does not have a significant effect.

We report on the experimental study of the stability of ultrashort pulse (USP) generation. Two types of mode-locking (ML) mechanisms were carried out in an Er-doped fiber laser: first, passive ML based on the nonlinear polarization evolution (NPE) and second, hybrid ML based on high-density, well-aligned single-walled carbon nanotubes (HDWA-SWCNT) as a saturable absorber (SA). The output pulse characteristics of both states were compared. The average output power was 28.8 and 29.96 mW, with pulse durations of 174 and 211 fs for NPE-based ML and hybrid ML, respectively. The maximum level of the relative intensity noise (RIN) was -130.35 dBc/Hz for NPE-based ML and -133.83 dBc/Hz for HDWA- SWCNT-based ML in the frequency range of 476 mu Hz to 100 kHz. This result provides direct evidence of the high-frequency filter effect in the nanotubes used. Furthermore, the measured value of the deviation of the pulse repetition frequency in a time interval equal to 1 s was 1.9610(-7) and 1.3310(-7) for the ML mechanisms of the NPE and hybrid modes, respectively.

A study of the optimal parameters of a distributed fiber microphone circuit based on a laboratory setup of a phase-sensitive optical reflectometer (φ-OTDR), which reproduces the work of φ-OTDR at one point, has been carried out. Various schemes for constructing a microphone based on φ-OTDR and various sampling rates of the analog-to-digital converter are investigated. The optimal configuration of the φ-OTDR circuit is substantiated, which made it possible to ensure high quality of human speech recognition during voice recording by the proposed method with a sampling frequency of 40 kHz. In a standard phrase based on Harvard sentences containing 80 words, 71 words were recognized, i.e., 88.75

We report the experimental generation of soliton molecules (SM) with a controlled number of pulses in an all-fiber erbium laser. The change in the number of pulses (from 7 to 18 coupled states) occurred without changing time-separation between pulses. The ability to increase or decrease the number of pulses is repeatable and easily controlled by changing the pump power in both directions without changing the output characteristics of the reported regime. The average pulse duration was < 0.5 ps at full width at half maximum with a time interval between pulses of similar to 4.7 ps. We also experimentally and numerically studied the evolution of soliton molecules regime with N = 23 during propagation along a standard telecommunication fiber with anomalous dispersion. In this case, we observed the appearance of a dispersive wave, which led to a rapid broadening of the pulses and the subsequent decay of the SM.

Distributed optical fiber sensors are important for continuous remote monitoring of large infrastructures, such as gas and oil pipelines, civil controlled perimeters, dams, roads, railroads, and also telecommunication networks. We present the theoretical study and practical implementation of a phase-sensitive distributed fiber sensor, capable of real-time monitoring of an urban area telecommunication network. The traditional data processing is here enhanced by CNN machine learning algorithms providing recognition accuracy >98 % for different perturbation or intrusion processes in the inspection wells located along the fiber network. In addition to this specific application to a telecommunication network, other applications of this fiber sensor are possible -and also already implemented- for gas&oil pipelines, railroads, power plants, and transportation and industrial sites in general.

In this article, we report on experimental studies of the influence of several laser radiation parameters, such as the duration of the laser pulse, the radiation wavelength, and the pulse energy, on the efficiency of the destruction of urinary calculi. The study used a laser lithotripter based on a fiber Tm laser generating at a wavelength of 1940 nm with pulses with a duration of about 1800 μs and pulse energy of up to 6 J, as well as a femtosecond solid-state Yb laser generating at a wavelength of 1032 nm with a pulse duration of about 250 fs and pulse energy of up to 400 μJ. A comparative analysis was carried out according to such criteria as the productivity of lasers when removing a unit mass of images and the amount of sample displacement resulting from the retropulsion effect. The results obtained in this work demonstrated that the femtosecond laser loses approximately two times its efficiency in terms of sample material removal. However, this shows the absolute advantage of the photoionization mechanism of femtosecond laser ablation in the study of retropulsion and thermal heating, which were completely absent in this case.

An instrument and technique for assessing errors of measuring optical surface radius of curvature with a laser rangefinder are presented. Errors of optical instrument alignment with a wave-front sensor are shown to influence the accuracy of measuring the mirror radius. Errors of the rangefinder-aided technique for measuring the surface radius are estimated. A computer analysis shows that the developed scheme of misalignment measurement allows a relative error of 0.02 – 0.3 % to be attained for mirrors ranging in radius from 1 m to 10 m. The choice of the accuracy characteristics of the rangefinders used for measuring the optical surface radius of curvature is justified.

The choice and justification of optimal wavelengths of spectral radiance density registration for the task of monitoring methane emissions in the atmosphere from the orbit of an artificial satellite by a passive optical sensor in the spectral region near 1.65 μm have been performed. Mathematical modelling of the spectra recorded by the optical sensor for tropical and subarctic atmospheric models of the Earth’s atmosphere, different widths of the spectral function of the acousto-optic spectrometer, and different solar zenith angle were performed. It is assumed that methane emissions in the Earth’s atmosphere will be monitored from a promising nanosatellite (weighing less than 6 kg) using an acousto-optic spectrometer, which uses two narrow (0.1 nm and 0.5 nm) wavelengths of radiation registration to implement a differential method of absorption spectroscopy based on acousto-optic filtering. A criterion for selecting optimal wavelengths for monitoring the integral methane content in the atmosphere from the orbit of the artificial satellite is proposed. The values of the central wavelengths of optimal wavelengths for recording the energy brightness of scattered radiation for the width of the spectral function of the acousto-optic spectrometer in range (0.0, 0.1, 0.2 and 0.5) nm have been obtained. It is shown that the choice of the optimal pair of wavelengths is determined by the width of the spectral function of the sensor, depends insignificantly on the model of the Earth’s atmosphere (tropical or subarctic model) and does not depend on the solar zenith angle in range (0–80) angular degree.