Compact diode-pumped chirped pulse regenerative amplifier systems with pulse repetition rate of hundreds kilohertz based on Yb³⁺-doped crystals are of practical importance for wide range of applications such as materials processing, medicine, scientific research, etc. The aim of this work was to study the Yb³⁺:LuAlO crystal based dual wavelength chirped pulse regenerative amplifier.

Perovskite-like aluminate crystals have unique spectroscopic properties that allowed to use amplifier active element gain spectrum as an amplitude filter for amplified pulse spectrum and even obtained dual wavelength amplification without any additional components.

In our work a simple way to obtain dual-wavelength operation of chirped pulse regenerative amplifier by using the active medium gain spectrum as an amplitude filter for the formation of the amplified pulses spectrum demonstrated for the first time to our knowledge. Maximum output power of 5.4 W of chirped pulses (3.8 W after compression) and optical-to-optical efficiency of 22.5 % have been obtained for Yb:LuAP E//b-polarization at 200 kHz repetition rate. Compressed amplified pulse duration was about 708 fs while separate spectral components durations were 643 fs and 536 fs at 1018.3 nm and 1041.1 nm central wavelengths, respectively. Performed investigations show high potential of Yb³⁺:LuAP crystals as active elements of compact diode pumped chirped pulse regenerative amplifiers

The searching and designing new solutions for mirror systems, including afocal ones, has been studied for decades. In the design, it has always been difficult to combine optimization and cost. Nowadays, the problem remains relevant. The widespread use of mirror systems is due to some aspects: thermal stability, high resolution in a wide spectral range, and the absence of image defects due to chromatic aberrations. All this provides superior performance compared to lens systems. The purpose of this paper is the design of two compact afocal mirror systems with small axial dimensions.

Schemes of afocal three mirror systems with small axial dimensions are presented. The schemes can also be called compacts. A study was made of systems in which the diameter of the aperture diaphragm in the primary mirror is modified, which leads to a more compact system.

A calculation algorithm of new the systems is proposed, with correction of the image curvature. A summary of formulas of the main parameters of the system is given, and various design solutions are calculated for angular field of view 2ω = 20ˈ and diameter of the entrance pupil D = 35 and D = 70 mm.

Computer simulations were performed in the Opal, Zemax, and Code V software. The designed systems have good correction of aberrations for the given characteristics: in the spot diagrams, the values of the RMS scatter spot do not exceed 1,35 μm; GEO radius (distance from the reference point) – 0.105 μm; together with Airy disk sizes of about 9.16 μm, indicating that the images are close to diffraction.

The calculated systems can be successfully applied as part of a more complex system, as well as in systems with a synthesized aperture.

For the effective use of dielectric sensors, optimization of the design parameters of the sensors, such as the depth of penetration of the electromagnetic fi and the magnitude of the sensor signal, is of great importance. The purpose of the work was to build a mathematical model of a sensor with an open area of space and calculate its parameters.
Results of main parameters calculations of the open space sensor are presented. Methods of integral equations and mirror images are used for numerical 2D modeling. The surface of each electrode was considered as two parallel lamellae. This approach simplifi the procedure for numerically solving a two-dimensional problem. It allows you to calculate the electric fi of fl layered media with less time, using less powerful computers. The numerical calculation program is implemented in MAPLE.
The program adequacy was checked for a sensor made on one-sided foil Tefl (ε1 = 2,3) with a thickness of b = 1.0 mm. The electric fi was calculated for the sensor in a three-layer medium. The calculated picture of the fi showed that the distribution of force lines is not uniform. It was found that the depth of the control zone does not depend on the metallization of the sensor surface. The depth of the control zone for an open-type sensor is in the same range as the depth of the control zone for fl overhead measuring capacitorsan analog of fringing electric fi d (FEF) sensors.

One of the most important parameters of powerful hydro generators (HG) is the air gap between the rotor and the stator, and its deviation from the set norms is a defect that can lead to serious accidents. Therefore, the size and shape of the gap must be monitored both during inspections and during operation of the machine. The aim of this paper was to develop a secondary measuring transducer providing accuracy and resolution for a capacitive gap sensor formed by coplanar parallel electrodes.

It is shown that the reliability and safety of operation of powerful HG inextricably depend on the timely detection of their defects, especially during operation. One of the most important parameters of the HG is the air gap between the rotor and the stator, and its deviation from the set norms is a defect that can lead to serious accidents. Therefore, the size and shape of the gap must be monitored both: during inspections and during operation of the machine. The paper discusses the features of measuring the air gap in a powerful HG, as well as existing modern methods and means of measurement.

It is shown that for measuring the gap in capsule HG, one of the most suitable means is a meter, which includes a capacitive sensor mounted on a central bore of the stator core. Commercially available gap meters with capacitive sensors are not suitable for use on HGs. Commercially available meters with capacitive sensors, by their certain characteristics, are not always suitable for use on HGs.

A secondary measuring transducer with improved characteristics is proposed for a capacitive gap sensor formed by coplanar parallel electrodes.

The converter is developed on the basis of a balanced compensation bridge measuring circuit. The control action in the device is formed by the phase of the unbalancing signal.

The structural diagram of the converter is presented and the algorithm of its operation is described. The process of forming a measuring output signal proportional to the sensor working capacitance in the circuit is considered.

The use of a capacitive sensor with coplanar parallel electrodes and the proposed secondary measuring transducer will ensure high accuracy and resolution when measuring the air gap.

Computer simulations are commonly used to support design and optimisation of powerful negative ion sources for the needs of future thermonuclear reactors like e. g. ITER. The aim of the paper was to study changes of produced beam quality (described by its emittance and brightness) with the geometry of the extraction system as well as extraction voltage.

A two-dimensional Particle-in-Cell (PIC) method based code was applied to model Hions and electrons extraction from the ion source plasma chamber through the opening with bevelled surface. The root-meansquare emittance of the extracted beam was calculated according to Chasman and Lapostolle approach. Ion beam phase space portraits were also presented to enrich the discussion.

Growth of ion (electron) beam emittance was observed both with the increasing radius of the extraction opening and the inclination of its bevelled surfaces. This degradation of beam quality is partially balanced by increasing extracted Hion current. On the other hand, increasing length of the extraction channel improves the beam quality.

It was demonstrated that for wider extraction opening the Hion beam consist of two parts coming form the two different regions of the chamber. According to calculated beam brightness the optimal wall inclination was found to be near 26o in the studied case. The decrease of the beam emittance saturates for larger channel length values. In the considered case the optimal channel length was h = 1.7 mm. The evolution of ion beam emittance and brightness shows that the best beam quality is achieved for extraction voltages between 0.5 kV and 2 kV.

The sensor design features and the sensing material properties which can influence the response time of the polymer-based capacitive humidity sensors are shortly discussed. The ways of specifying the dynamic properties of capacitive humidity sensors in technical data sheets by the leading companies on the market are briefly characterized and discussed.

The schematic view and operation of the experimental setup for determining of the dynamic parameters of capacitive humidity sensors at different temperatures of humid air are described. The dynamic behaviour of polymer-based capacitive humidity sensors was registered as the measurement profiles for both positive and negative step changes in humidity level. The response and recovery times, as well as the time constants for the exponential approximation fits of the step responses, were determined either graphically or analytically, based on the collected data.

The changes of these parameters under atmospheric pressure within the temperature range from – 30 °C to + 20 °C were analysed. The exemplary transient measurement profiles are shown, together with the illustrations of the graphical method for determining the response and recovery times. Also, the plots of the relationship between response and recovery times as well as time constants, and temperature, are presented. Some explanations of the obtained results are suggested.

The article exposes description of features of the combined approach application to the evaluation of measurement results uncertainty. The aim of this work is the justification and development of new science-driven approaches to achieve maximum efficacy of measurements on the criteria "accuracy/costs" at the stated level of confidence.

It provides theoretical base for correctness of combined approach to assess measurement results uncertainty. There is proposition to conventionally divide measurement process into fragments – combining objects, each from shall be considered as individual element for evaluation. It is well known that combining objects can be formed by grouping individual components (resources) of the measurement process either via separate stages of the measurement process.

Correctness of such approach is based on the application of "resource" and "process" approaches as regards identification of the factors that affect the measurement results uncertainty. This article provides recommendations on selection of model or empiric approach for evaluating of particular contributions from combining objects of different types into total uncertainty of the final measurement result. In order to improve the validity of empiric approach of the criteria of sufficiency of measurement method uncertainty examination was formulated. It is recommended to evaluate the total uncertainty of the final measurement result by complexation of evaluations of particular total uncertainty of the results for all fragments according to the uncertainties distribution law.

It is determined two typical cases of effective application of the combined approach to evaluation of measurement results uncertainty: method of direct measurements and method of indirect measurements. This article considers features of effective application of the combined approach for both situations providing corresponding examples. Special attention is paid to the application of the combined approach to assessing the test results uncertainty. As distinct from the measurement process realized under normal conditions, testing process includes additional external influence factors that are determined by test conditions.

Receiving modules of single-photon communication systems should provide the smallest loss of transmitted information when measuring low-power optical signals. In this regard, it is advisable to use photon counters. They are the most highly sensitive, but characterized by data recording errors. The aim of this work was to develop a method for determining the intensity of recorded optical signal in a singlephoton communication channel with a receiving module based on a photon counter, which ensures the least probability of erroneous registration of transmitted binary symbols.

Methods of achieving the least loss of information in asynchronous photon binary communication channel with a receiver-based photon counter has been developed. A device for implementing this methods has been created. The method is based on using the statistical distribution of the mixture of the number of dark and signal pulses received at the output of the photon counter when registering binary symbols "0" P_st 0 (N ) and symbols "1" P_st 1 (N ). The essence of the method consists in determining the intensities of optical signals for transmitting binary symbols ("0" and "1") and threshold levels of the pulses N₁ and N₂ registered at the output of the photon counter. 

The method allows to determine the lower and upper threshold levels of recorded pulses and the intensity of optical signals in the transmission of binary data. Moreover, the probability of erroneous registration of binary symbols is minimal.