Brightness Amplifier Research Articles

Semi-empirical model of a copper bromide vapor brightness amplifier

We propose the semi-empirical mathematical model of the brightness amplifier based on the self-terminating transitions in laser active media. The model is applied to the copper bromide vapor brightness amplifier. The feature of the model is that it allows one to distinguish the amplified spontaneous emission and amplified input optical signal. Due to that we have managed to study the “real” gain and theoretical maximum of contrast for the brightness amplifier depending on temporal and energy characteristics of the input optical signal.

Super broadband light source: a promising master oscillator source for high brightness and high-power fiber amplifiers.

Stimulated Raman scattering (SRS) and transverse mode instability (TMI) effects are crucial limitation factors for further power scaling of high-power fiber amplifiers with near-diffraction-limited beam quality. It is an important research direction to carry out laser system optimization from the perspective of seed construction. In this work, we experimentally investigated the impact of utilizing different seed lasers on the SRS and TMI characteristics in high power ytterbium-doped fiber amplifiers. Both the phase modulated single frequency fiber laser (PMSFL), fiber oscillator laser (FOL), and superfluorescent fiber source (SFS) as a typical type of temporally stable broadband light source (SBLS) are employed as seed lasers. The experimental results indicated that the SRS intensity in the fiber amplifier is influenced by the properties of the seed laser source. Notably, the SRS threshold of the SBLS could be comparable to that of a low-noise PMSFL source. There is a significant increase in TMI threshold when employing SBLS as a seed laser in high-power fiber amplifiers, which is 3.86times that of the injected seed laser with a 3dB narrow linewidth of 0.74nm. Considering the combined threshold characteristics of SRS and TMI, it can be found that SBLS is a promising master oscillator source for high brightness and high-power fiber amplifiers. Our work could provide a good reference for the selection of a master oscillator source, and we believe that it is an important direction to go beyond the power limitation of high-power fiber lasers by constructing a light source with broader spectral linewidth and temporal stability.

A Dual-Branch Autoencoder Network for Underwater Low-Light Polarized Image Enhancement

Underwater detection faces uncomfortable illumination conditions, and traditional optical images sensitive to intensity often cannot work well in these conditions. Polarization imaging is a good solution for underwater detection under adverse lighting conditions. However, the process of obtaining polarization information causes it to be more sensitive to noise; serious noise reduces the quality of polarized images and subsequent performance in advanced visual tasks. Unfortunately, the flourishing low-light image enhancement methods applied to intensity images have not demonstrated satisfactory performance when transferred to polarized images. In this paper, we propose a low-light image enhancement paradigm based on the antagonistic properties of polarization parameters. Furthermore, we develop a dual-branch network that relies on a gradient residual dense feature extraction module (GRD) designed for polarized image characteristics and polarization loss, effectively avoiding noise introduced during the direct amplification of brightness, and capable of restoring target contour details. To facilitate a data-driven learning method, we propose a simulation method for underwater low-light polarized images. Extensive experimental results on real-world datasets demonstrate the effectiveness of our proposed approach and its superiority against other state-of-the-art methods.

Optimization of the CuBr＋Ne＋HBr brightness amplifier operating mode for high-speed imaging

The paper presents the research and development of a low-volume brightness amplifier for imaging laser active optical systems (laser monitors) with a pulse repetition frequency (PRF) of up to 100 kHz. A small-sized active element and pumping source based on tasitron have been developed. The effect of the brightness amplifier’s operating features (concentration of CuBr and HBr) on the numerical characteristics of images obtained in the laser monitor has been studied. The optimal concentrations were determined, and it was proven for the first time that they should be 30% lower than what is needed for obtaining maximum laser power. It was shown that increasing the CuBr concentration leads to a decrease in the field of view. The effect of the one-pass amplification profile on the quality of LOAS-based images was experimentally determined. A small-sized active element (40 cm3) excited with a specific pulse energy input of 238 μJ/cm3 can be used to obtain images with a time resolution of up to 10 μs.

Многофункциональная система визуализации на основе лазера и усилителя яркости на парах бромида меди

A multifunctional system meant to image the surface of energetic materials during combustion based on copper bromide vapor gain media is proposed. The system allows quickly implement various methods of active visualization and is based on a high-speed video camera, an illuminating laser, and a copper bromide vapor brightness amplifier. Depending on imaging needs, the main components of the system can be configured as a laser-illuminating system, a single-channel laser monitor, or a laser monitor with synchronous laser illumination. A high-voltage pulsed power supply allows connecting both one laser tube and two at the same time, while switching operating modes can be carried out on- the-fly. The source generates one or two synchronized sequences of high-voltage pulses for pumping gasdischarge tubes with a voltage of up to 6 kV and a frequency of 20 kHz. Due to the use of gas discharge tubes with independent control of temperature parameters, the operating modes with a pump power of 500–700 W for each channel can be realized. To generate pump pulses for laser media, a two-channel thyratron circuit for the direct discharge of storage capacitors were used, charged by a common stabilized voltage source provided by a step-down pulse stabilizer and a pulse shaper for charging storage capacitors based on a bridge inverter. A transistor modulator with adjustable delay lines carries out synchronization of the laser illumination and the brightness amplifier in the mode with synchronous laser illumination with an accuracy of ±1 ns.The experimental data of the system operation in various modes are presented. The imaging results for the surface of mixtures of metal nanopowders during combustion, obtained with various configurations of the laser system, are presented.

High-speed optical imaging technique for combusting metal nanopowders

This paper discusses a technique for studying laser initiation and combustion of high-energy materials in real time using a two-channel video recording system. Traditional high-speed imaging is used as one channel, and a brightness-amplified laser projection system (laser monitor) is used as the second channel. The synchronization of laser ignition and high-speed imaging of the flame and the sample surface is considered in detail. The relationship between the propagation of the flame glow and the change in the surface of the nanoAl + MnO2 thermite mixture during combustion has been established. A method of simultaneous high-speed recording of images of a laser monitor by two cameras with different recording frame rates is proposed to provide the possibility of studying the initial stage of combustion and the entire combustion process of the same nanopowder sample with different temporal and spatial resolutions. Imaging of the surface of nanoAl + MnO2 thermite mixtures at a recording frame rate of 20,000fps has been implemented using a laser monitor. The possibility of determining the propagation velocity of the combustion wave on the surface of the sample is demonstrated to be up to 85 mm/s. The influence of the exposure time of a high-speed camera on the image quality of a laser monitor is investigated. It is demonstrated that the image quality is almost the same for the images formed by 1–9 emission pulses of the brightness amplifier.

Physical bases of meteor registration methods and the instrument complex of the NKU Observatory

One of the actual directions of studying the physical characteristics of near–Earth space is the assessment of the concentration of meteoroids in it, and the time change of this parameter. In this regard, the principles of setting and implementing meteor observations at the observatory of the North Kazakhstan university named after Manash Kozybayev are considered in chronological order. Meteor observations were carried out on the basis of an integrated approach, including the use of meteor patrols, an All Sky camera, a system for recording radio wave reflections from a remote station from meteor tracks, and a camera based on an optical image intensifier.  Based on the analysis of the practical experience of using this equipment, the advantages and disadvantages of each of the methods of meteor registration are revealed. It is shown that the use of the latest image brightness amplifiers and wide–angle cameras with the highest possible sensor sensitivity is the most progressive for their optical observations. The closest attention is paid to the analysis of the experience of implementing the registration of plasma meteor tracks in the radio range. The method is based on the selection of reflected (scattered) musical–speech signals of a remote radio station having a specific pulse structure. Comparison of the obtained results on the frequency of meteor phenomena with the data of known observation points allows us to speak about the effective operation of the newly created meteor monitoring system in the radio range. In the final part of the work, ways to improve the efficiency of recording meteor phenomena in the optical range based on the use of the latest radiation receivers are considered.

Synchronized Two-Camera Laser Monitor for Studying Combusting Powder Systems

In this paper, we offer a laboratory facility for in situ visualization of the combustion of ultrafine metal powders, which combines laser initiation and simultaneous high-speed recording of images of the flame of a burning material and a surface covered by a flame. Visualization of the surface through the flame is realized using a laser monitor—an optical projection system with brightness amplification. The proposed imaging system makes it possible to get more detailed information about the combustion process, in particular, to study the change in the surface through the flame in the area of laser initiation, and the propagation of heating and combustion waves over the sample, as well as to study the change in the surface reflectance during combustion. To study the area of laser initiation, it is proposed to simultaneously record images of a laser monitor with two cameras. The symmetry of the combustion wave front propagation and the combustion products’ formation during laser initiation of the nanoAl + Fe3O4 thermite mixture was demonstrated. The nature of propagation in the form of a ring is a consequence of the symmetry of the properties of the system under study, at the micro and macro levels.

Solid Energetic Material Based on Aluminum Micropowder Modified by Microwave Radiation

The paper discusses the application of pulsed microwave radiation for the modification of crystalline components of a high-energy material (HEsM). The model aluminized mixture with increased heat of combustion was studied. The mixture contained 15 wt.% aluminum micron powder, which was modified by microwave irradiation. It was found that the HEM thermogram has an exo-effect with the maximum at 364.3 °C. The use of a modified powder in the HEM composition increased the energy release during combustion by 11% from 5.6 kJ/g to 6.2 kJ/g. The reason for this effect is the increase in the reactivity of aluminum powder after microwave irradiation. In this research, we confirmed that the powders do not lose the stored energy, even as part of the HEM produced on their basis. A laser projection imaging system with brightness amplification was used to estimate the speed of combustion front propagation over the material surface. Measurement of the burning rate revealed a slight difference in the burning rates of HEMs based on irradiated and non-irradiated aluminum micropowders. This property can be demanded in practice, allowing a greater release of energy while maintaining the volume of energetic material.

High-speed metal vapor brightness amplifier for visual inspection and diagnostic systems

High-speed metal vapor brightness amplifier for visual inspection and diagnostic systems

ЕФЕКТИ ЕЛІПТИЧНОСТІ ГРАВІТАЦІЙНО-МІКРОЛІНЗОВАНОГО ДЖЕРЕЛА ВИПРОМІНЮВАННЯ З РОЗПОДІЛОМ ЯСКРАВОСТІ СТЕПЕНЕВОГО ТИПУ

Gravitational microlensing of elliptical sources in the linear caustic approximation is considered, based on the formula for the power-law distribution of brightness over the source plane; , where . This expression is convolved with the brightness amplification of the point source (linear caustic approximation). We have constructed the total amplification coefficients (amplification curves) that allow us to estimate the increase in the integral brightness of the source in microlensing processes for various orientations with respect to the linear caustic. The averaged amplification curves are built within the framework of a simplified statistical model when the source is crossed by linear caustics with an isotropic distribution of velocities (with fixed caustic strength and velocity modulus) , . The value of appears to be independent of the model parameter . The resulting estimates are qualitatively consistent with the conclusions obtained for the Gaussian source model, although there are differences related to the shape of the source brightness distribution. The results show that in view of the accuracy of the modern photometry, the effects of ellipticity are significant; however, they are obscured by other effects due to various conditions of a specific microlensing event. Moreover, registration of the ellipticity signal in real observations requires long-term monitoring with a large number of microlensing events.

A CuBr-Based Brightness Amplifier with a Repetition Frequency of Superradiance/Amplification Pulses up to 200 kHz

A CuBr-Based Brightness Amplifier with a Repetition Frequency of Superradiance/Amplification Pulses up to 200 kHz

Two-brightness-amplifier imaging system for energetic-materials-combustion study.

This paper discusses a laser monitor with two channels for acquiring images synchronized in time and its use for visualizing the surface of metal nanopowders during combustion. Each channel is an independent optical system based on a copper bromide vapor brightness amplifier and a high-speed camera that allows visualizing a specified area of the sample. Thus, the laser monitor allows real-time imaging of the same sample area with different spatial resolutions and simultaneously two areas of the sample. In comparison with the "master oscillator-power amplifier" system and a bistatic laser monitor in the proposed system, the radiation pulses of the brightness amplifiers are synchronized in such a way that the inversion in the active media is formed at different time intervals. Such a system makes it possible to register processes in one area of the sample in the mode of double frames with a time shift of 35ns. As an additional option in the proposed system, it is possible to implement a laser illumination mode in which an additional camera is used with a narrow-band filter installed on it for the emission wavelength of brightness amplifiers, and the same radiation from the brightness amplifier is used as an illuminating light source. The proposed technique was used to visualize the combustion of aluminum nanopowders without additives in real time in the area of laser initiation with different spatial resolutions and nanoAl + microAl + microFe powder mixtures in the laser ignition area and the adjacent area of the sample simultaneously as the combustion wave propagates.

A Laser Monitor with Independent Lighting and Brightness Amplification for Imaging High-Temperature Combustion of Metal Nanopowders

A Laser Monitor with Independent Lighting and Brightness Amplification for Imaging High-Temperature Combustion of Metal Nanopowders

Random forests for statistical modeling of experimental data for CuBr vapor lasers used as brightness amplifiers

This study demonstrates the high capabilities of data mining and the random forest (RF) machine learning technique for processing experimental data in the field of laser equipment and technology and extracting significant information from these. The subject of study is the copper bromide vapor laser, used as a brightness amplifier and as an active medium in active optical systems actively developed in recent years. Published data from 465 experiments on this type of laser are statistically examined. RF regression models are built to predict the output power as a basic laser characteristic. The dependence of the output power on the input electric power, the pulse repetition frequency, the pressure of the additional gases in the discharge, and other operating and geometric parameters of the laser is determined. The models fit up to 98% of the experimentally measured laser output power data.

Двухканальный лазерный монитор для наблюдения процессов высокотемпературного горения нанопорошков металлов

A laser monitor with two image acquisition channels based on two brightness amplifiers and two digital cameras is presented. The laser monitor makes it possible to visualize the surface of metal nanopowders during combustion simultaneously in two regions of the sample or in one region with different magnifications. The delay between the radiation pulses of the brightness amplifiers is set in such a way that the radiation of one brightness amplifier does not affect the image formed by the other brightness amplifier. The proposed experimental technique makes it possible to study the surface of samples of powder materials during high-temperature combustion, accompanied by intense glowing and scattering of combustion products. The use of two-channel visualization makes it possible to study the surface of a burning sample in more detail, in particular, to study the inhomogeneity of the combustion process.

CuBr-усилитель яркости с частотой следования импульсов сверхизлучения/усиления до 200 kHz

The paper presents the results of research and development of a high-speed brightness amplifier based on copper bromide vapor active medium, with a pulse repetition frequency of up to 200 kHz. This became possible due to the use of the reduced input energy into the discharge mode (less than 60 µJ / cm3 per pulse), by shortening the leading edge of the high-voltage pump pulse to 20 ns and the duration (at half-height) to 30 ns.

Two-Channel System With Brightness Amplification for Monitoring the Combustion of Aluminum-Based Nanopowders

Two-Channel System With Brightness Amplification for Monitoring the Combustion of Aluminum-Based Nanopowders

In situ nanopowder combustion visualization using laser systems with brightness amplification

In this paper, we report on an experimental demonstration of a new technique for real-time monitoring of the air combustion of aluminum-based nanopowders and mixtures. An optical system having a brightness amplifier is used for sample-surface imaging during high-temperature combustion. The main advantage of the laser-monitor application, compared with direct high-speed imaging, is the possibility of seeing through the intense glowing of a burning sample. Furthermore, the proposed laser monitor has an increased monitoring distance compared with known systems, which is provided by a mirror-imaging scheme applied to the laser monitor. The proposed technique allows real-time monitoring of high-temperature combustion processes accompanied by intensive lighting and product scattering at a distance of up to 50 cm from the optical system. The operation of the optical system is tested using both a quietly burning aluminum nanopowder and aluminum-based explosive mixtures. The combustion of a nanoAl+µAl+µFe powder mixture and aluminized blended propellant is visualized using a laser monitor for the first time.

Operating features of a copper bromide brightness amplifier in the monostatic laser monitor

The paper presents the research results of operation features of the copper bromide brightness amplifier in the monostatic laser monitor with frame-by-frame imaging. The dependence of the gain on the input signal level is determined. The small-signal gain reaches 0.22 cm−1 without the hydrogen-containing additive. It is proposed to estimate the sensitivity of a laser monitor based on the analysis of digital images formed by a single pulse amplification. The influence of the input signal energy attenuation on the contrast of images formed in the monostatic scheme of the laser monitor is established. The sensitivity of the copper bromide brightness amplifier in the laser monitor is experimentally determined. It is shown that the minimal level of input signal required to form the image with a contrast sufficient for mathematical processing is 1.4% of ASE power. The sensitivity of the laser monitor is limited by the power of “technical” noise caused by parasitic reflections from elements of the optical scheme.