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A sensor of refractive index of analytical liquid operating in the Kretschmann geometry and based on an oblique-incidence reflection interferometer (RI) is simulated for the first time, and its spectral properties are investigated. The principle of operation of the sensor is based on the effect of inverted surface plasmon resonance (ISPR). The sensitive structure represents the metal–dielectric multilayer coating consisting of thin nickel film in combination with quarter-wave dielectric layers. Simulation of the principle of RI fabrication under oblique incidence of light is described. Expressions governing sensitivity, spectral width of the ISPR-induced maximum in reflection, along with the figure of merit, are derived. It is demonstrated that this type of sensor can exhibit extremely high values of the figure of merit (>103) due to high Q factor.

We investigate possibilities of using a multicore fiber containing fiber Bragg grating (FBG) in sensing applications. We use the advantages of the femtosecond point-by-point technique to inscribe FBGs in the selected cores of polyimidecoated 7-core fiber. Besides the results on 3D shape sensing we present new approaches for acoustic wave detection and environment refractive index sensing. In particular, we show that spatial division multiplexing with a multicore fiber allows one to create multipoint acoustic sensor based on a single laser source. In addition, to detect the change in environment refractive index by using point-by-point FBG, there is no need in fiber coating removal. Thus, durability of the fiber along with the FBG inscription approach is of great potential for fabrication of next generation multiple parameter sensors.

Formation of highly ordered nanostructures on a crystalline silicon surface is highly demanded for novel optoelectronic and nanophotonic designs pushing toward development of inexpensive and high-performing nanostructuring technologies. Here, we demonstrate that laser-induced periodic surface structuring of c-Si protected by a thin Hf over-layer allows one to fabricate extremely uniform high-aspect-ratio gratings with a characteristic periodicity of ≈900–950 and 450 nm. Corresponding ordering originates from interference of incident IR femtosecond laser pulses with surface plasmons as well as doubling of the grating period via interference of counter-propagating plasmons. A high-melting-point Hf over-layer regulates the c-Si ablation in the plasmon-mediated interference maxima and prevents its excessive oxidation upon multi-pulse exposure in ambient environment. Considering unique high-aspect ratio morphology (a depth-to-period ratio of up to 1.24 and a depth-to-width ratio of up to 8) of the reported nanogratings, their outstanding uniformity, and rather fast printing rate of ≈0.2 mm2/s as well as possibility for its further upscaling, we envision high practical applicability of this technology in novel optoelectronic devices, visible and near-IR optics, all-dielectric metasurfaces, and sensors.

Various issues of creation of diffractive optical elements transforming one laser beam with small divergence to a matrix of converging beams with a diffraction size of focused spots in the plane of object illumination and their application for problems of DNA sequencing and microscopy are considered. The parameters of diffractive elements are calculated and optimized in the approximation of the Fresnel–Kirchhoff diffraction theory. Diffractive elements are fabricated by the method of direct laser writing on a photoresist by using a circular laser writing system. Experimental characteristics of a diffractive element creating a matrix consisting of 33 × 33 beams, which are focused in one plane at a distance of 210 mm, are presented. The degree of nonuniformity of beam intensities determined by the ratio of beam intensities in the central region to intensities of peripheral beams is 1/2.5, which is potentially sufficient to be used in DNA sequencing problems. The maximum distortions of spot positions in the entire focusing field is

We have demonstrated the possibility of making a Raman laser with a random distributed feedback ensured by an array of 57 fibre Bragg gratings with random phases and amplitudes inscribed in a 13-m-long polarisation-maintaining passive fibre. The linearly polarised cw output power at a wavelength of 1092.3 nm reaches 5.7 W. The laser linewidth at the highest output power is about 80 pm. In the nearthreshold regime, we observe single-frequency lasing with a linewidth under 100 kHz as determined by self-heterodyne measurements.

We use 7-core optical fiber containing Fabry-Perot interferometers for a spatial division multiplexing of acoustic sensors. The interferometers are inscribed in different cores of the fiber using the femtosecond point-by-point inscription technique.

We present the results of high-ordered surface structure formation by femtosecond laser pulses $(\lambda$ =1026 nm, $\tau$ =232 fs) using an astigmatic Gaussian beam on the surface of thin metal films (thickness 30–40 nm) of Cr and Hf sputtered on the glass substrate. The difference in the structure quality and formation performance between the cases of Cr and Hf metal films was analyzed. The fabrication productivity increase by an order of magnitude was achieved in the case of Hf metal film.

The paper presents the results of the thermochemical laser-induced periodic surface structures formation on Cr film at femtosecond irradiation with elliptical spot shape at different powers, repetition rate and scanning speeds.

Numerical modelling demonstrates the possibility of fabricating an all-fibre multibeam two-mirror reflection interferometer based on a metal–dielectric diffraction structure in its front mirror. The calculations were performed using eigenmodes of a double-clad single-mode fibre. The calculation results indicate that, using a metallic layer in the structure of the front mirror of such an interferometer and a diffraction effect, one can reduce the Ohmic loss by a factor of several tens in comparison with a continuous thin metallic film.

Experimental method of temperature and strain discrimination with fiber Bragg gratings (FBGs) sensors embedded in carbon fiber-reinforced plastic is proposed. The method is based on two-fiber technique, when two FBGs inscribed in different fibers with different sensitivities to strain and/or temperature are placed close to each other and act as a single sensing element. The nonlinear polynomial approximation of Bragg wavelength shift as a function of temperature and strain is presented for this method. The FBGs were inscribed with femtosecond laser by point-by-point inscription technique through polymer cladding of the fiber. The comparison of linear and nonlinear approximation accuracies for array of embedded sensors is performed. It is shown that the use of nonlinear approximation gives 1.5–2 times better accuracy. The obtained accuracies of temperature and strain measurements are 2.6–3.8°C and 50–83 μεin temperature and strain range of 30–120°C and 0–400 με, respectively.

The paper presents the results of the formation of thermochemical laser induced periodic surface structure on Cr thin films (40–350 nm) that was sputtered on the glass substrate. The different dependence of TLIPSS formation on processing rate in case of thin (40 nm) and thick (350 nm) is observed.

We consider the use of a two-mirror multibeam reflection interferometer as a selector of linear-cavity single-mode fibre laser radiation and present experimental data on continuous wavelength tuning of an erbium-doped fibre laser. Conditions are found for single-longitudinal-mode operation of the fibre laser cavity using a reflection interferometer, with the possibility of broadband wavelength tuning.

The paper presents the results of investigation of the thermochemical laser-induced periodic surface structures (TLIPSS) formation on metalls film (Ti, Ni, Cr) at femtosecond irradiation with different spot sizes, pulse powers, polarization directions. Also the results of selective TLIPSS etching for transfer a topology of TLIPSS into metal underlayer are presented.

In this paper, we present the study of the thermochemical laser-induced periodic surface structures (TLIPSS) formation on a thin chromium film under femtosecond laser (λ = 1026 nm, τ = 232 fs) irradiation focused on the astigmatic spot with an axis ratio of ≈1/10 and a width along the long side of 155 µm. The effect of the number of laser pulses and the repetition rate (2–200 kHz) on the formation of the structures is investigated. Variation of the number of pulses allowed us to observe the dynamics of the formation of structures. It has been found that the ordering of TLIPSS structures increases with increasing repetition rate of laser pulses, which is explained by the heat accumulation effect on the oxidation process and, consequently, on the formation of TLIPSS structures in the case of a high repetition rate of pulses, which is confirmed by the results of numerical modelling. This effect leads to a different oxidation dynamics and the formation of various types of oxides: predominance of CrO2 in the case of a high-rate impact and an increase in the contribution of Cr2O3 in the case of a low repetition rate of pulses.

A multibeam interferometer with oscillating mirrors is theoretically investigated. Transfer functions are presented and analyzed for two extreme cases, namely, for an interferometer with stationary mirrors and an interferometer operating in the mode of “superslow” mirror oscillations.

A multibeam interferometer with oscillating mirrors is theoretically investigated. The exact solution to the main equation for the interferometer and expressions for its transfer functions, i.e., generalized reflection and transmission factors, are obtained in a plane-wave approximation.

A total of 182 patients (95 men and 87 women) aged 15-49 years with insulin-dependent diabetes mellitus were treated using argon laser coagulation. Late results of laser therapy were followed up for 6 months to 3 years. In the patients with nonproliferative diabetic retinopathy (DR) on the fundus oculi the improvement consisted in partial resolution of solid exudative foci and retinal hemorrhages in 20%o of cases. In patients with preproliferative DR, soft exudative foci partially resolved and the number of retinal hemorrhages and microaneurysms decreased in 17%o of cases. In patients with proliferative DR, regressive development of proliferative tissue, desolation of newly formed vessels, and resolution of preretinal hemorrhages were observed in 13.9%o of cases. Stabilization for 3 years was attained in 75%) of patients with nonproliferative and proliferative and in 72.5%o of those with preproliferative DR.

A total of 185 children (93 boys and 92 girls) aged 6 months to 15 years and disease duration of 1 to 13 years, residents of different regions of Russia, were examined. Pathological changes of the retina caused by diabetes were detected on the fundus oculi of 56 (30.3%) children. In 42 (22.7%)) of these, the initial changes (solitary retinal hemorrhages, microaneurysms) and in 14 (7.6%)) more pronounced micro- vascular pathological changes typical of nonproliferative diabetic retinopathy were detected, in 2 patients - the proliferative stage. Later argon coagulation of the retina was carried out in 10 patients with nonproliferative diabetic retinopathy and in 2 with proliferative diabetic retinopathy. The initial stages of nonproliferative and proliferative diabetic retinopathy are an indication for laser coagulation in children. The status of 6 (50%) children improved in remote periods (6-24 months) after laser coagulation: hemorrhages resolved and microaneurysms decreased; in 4 (33.3%) children the process was stabilized. Deterioration was observed in 2 (16. 7%o) children with nonproliferative and proliferative diabetic retinopathy.

A technique of single-longitudinal-mode selection in a fiber laser by means of a fiber multiple-beam reflection interferometer (FRI) has been experimentally demonstrated for the first time. The laser is based on a semiconductor optical amplifier placed in a linear fiber cavity formed by a fiber Bragg grating (FBG), and the FRI generates at 1529.24 nm with output power of 1 mW in single-frequency regime with a linewidth of about 217 kHz and polarization extinction ratio of >30 dB. The FRI technique potentially enables fast tuning (within the FBG bandwidth of ~0.9 nm in our case) by varying the base length of the FRI that can be used in a number of practical applications.