Search

The paper is devoted to development of atypical excitation approaches of bistatic laser monitor active elements for the imaging of high-speed processes at a powerful background radiation. The practical significance is increasing the temporal resolution of the bistatic laser monitor, as well as improving the imaging parameters by minimizing the jitter of radiation pulses. To achieve this goal, semiconductor excitation sources of active media based on copper bromide vapor were developed, and their synchronization was performed in a pulse-repetition mode. The developed pump sources are set of identical commutation cells. Each cell contains storage capacitor, commutator and transformer. Powerful HGTG27N120BN insulated-gate bipolar transistors (IGBT) were chosen as commutators. Their switching storage capacitors are discharged through the primary winding of the transformer and as result the voltage pulse is induced in the secondary winding. The transformer load was the gas discharge tube (GDT) of the small-size brightness amplifier with the specified geometric parameters (l = 40 cm, d = 2.5 cm, V = 196 cm3). The simultaneous switching of 10 identical cells provided GDT breakdown. The radiation power of the active element in oscillator mode was 665 mW. The developed brightness amplifier with semiconductor pump source was used in the bistatic scheme of the laser monitor for the imaging of the test object. The pumping of the second active element, the illumination source (l = 90 cm, d = 5 cm, V = 1767 cm3), was performed by means of thyratron TGI1-1000-25. The pulse repetition frequency of the illumination source and the brightness amplifier was 10.5 and 21 kHz respectively. As result each second image was formed with increased brightness and contrast. The maximal jitter of radiation pulses in this case was 16 ns. The average jitter was 6 ns. Two identical semiconductor pump sources were tested simultaneously. The resulting array of waveforms (GDT current and GDT voltage) show that in most cases the jitter was completely absent, and when it appeared, it did not exceed 4 ns. The imaging at this configuration of the pump sources was not performed due to semiconductor source power (465 W) turned out to be insufficient for the excitation of the illumination source, and therefore options for increasing it were proposed. [ABSTRACT FROM AUTHOR]

• A new technique for imaging the combustion front of energetic materials has been implemented. • CuBr laser monitor with moving field of view is used for nanothermite combustion imaging. • Rotation of the concave mirror provides high-speed movement of the laser monitor beam. • The technique makes it possible to study the inhomogeneity of combustion through the flame. • The technique allows one to study combustion with variable rate. This paper discusses a technique for monitoring the combustion of high-energy materials in real time using a laser monitor modified to track the combustion front at the relatively long distance between the object of study and optical system. Options for moving the platform with the sample at a fixed beam of a laser monitor and a system with a motorized rotary mirror are considered. The system provides moving the observation area over the surface of the sample at an adjustable speed up to 22 cm/s. The advantages of the proposed technique are the possibility of high-speed control the combustion front propagation through the sample, full suppression of background lighting and the distance increasing when monitoring high-temperature objects. The paper presents the results of imaging the combustion in air of nanothermite compositions in a real time with movable field of view. The video images allow observing the changes in morphology of the nanopowder surface during combustion. In contrast to previously used laser monitors, the system allows studying the uniformity and linearity of combustion front propagation including the local burning rate at different moments of time. [ABSTRACT FROM AUTHOR]

• The new high speed imaging system is presented. • The results of Nd:Y2O3 laser evaporation are obtained. • It was experimentally demonstrated the ability of obtaining the images of prepossess under high intensive background radiation. • The diagnostic complex is designed to study the dynamic phenomena that occur in the interaction zone between a laser pulse and refractory oxides such as Nd:Y2O3, Fe2O3, ZnSe, and TiO2. The diagnostic complex is designed to study the dynamic phenomena that occur in the interaction zone between a laser pulse and refractory oxides such as Nd:Y 2 O 3 , Fe 2 O 3 , ZnSe, and TiO 2. This complex includes a compact brightness amplifier that utilizes copper bromide vapors, an optical objective, high-speed cameras (AOS Q-PRI and MegaSpeed-130MK), a digital synchronization system, a 1070 nm ytterbium fiber laser (LS-07N), a focusing lens, a quartz plate, a neutral density filter set, a pin photodiode (SFN2500FA), and a coaxial photocell (FEK-22). The active imaging system has a temporal resolution of 45 µs. Due to the intense glow of the laser torch resulting from the laser pulse impact on the target, it is not possible to capture images of the interaction zone and the evaporation process using passive filters. However, this issue is resolved by using the small-sized brightness amplifier (with dimensions of l = 38 cm, d = 1.5, V = 67 cm3), which allows for imaging of the droplets formed during the laser torch's presence. Additionally, the surface of the target in the interaction zone is also captured. The characteristics of the melt and the formation of large droplets during the laser pulse impact on the target are determined through this setup. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The results of research and development of a high-speed brightness amplifier based on an active medium on copper bromide vapors with a pulse repetition frequency of up to 200 kHz are presented. Operation at such repetition frequency was made possible owing to the mode of reduced energy input into the discharge (less than 60 μJ/cm3 per pulse) by means of shortening the front of the high-voltage pump pulse to 20 ns and the duration (at half-height) to 30 ns. [ABSTRACT FROM AUTHOR]

This work discusses the optical systems with brightness amplification based on two copper bromide brightness amplifiers for studying the combustion of aluminum-based nanopowders. It is proposed to use a system with brightness amplification and independent illumination–bistatic laser monitor to increase the brightness and sharpness of images. Independent illumination is realized using a second copper bromide laser and makes it possible to increase the exposure of the object under investigation in comparison with the conventional laser monitor with one brightness amplifier. In addition to independent illumination, a two-channel laser monitor is proposed to examine the surface of burning materials with different magnifications in one area of the sample, as well as simultaneously in two areas of the sample. The delay between the lasing pulses of the brightness amplifiers can be adjusted with high accuracy so that the radiation from one amplifier does not affect the images of the other. The proposed experimental technique makes it possible to investigate the surface of powder materials during high-temperature combustion, accompanied by intense glowing and scattering of combustion products. This article presents the results of real-time visualization of the surface of burning metal nanopowders and mixtures using bistatic and two-channel laser monitors. [ABSTRACT FROM AUTHOR]

A laser monitor system with independent brightness amplifier and a mirror scheme of image formation based on active copper bromide vapor medium is described that allows visualization of the surface of metal nanopowder during high-temperature combustion. Independent brightness amplification using second active element based on copper bromide vapor significantly increases the image contrast as compared to that in a laser monitor with single active element, which is advantageous for studying the surface of materials with low optical reflectance. In addition, it is demonstrated that a two-channel generator of pulses for pumping active elements on copper bromide vapor can be implemented on a single high-voltage power-supply source. [ABSTRACT FROM AUTHOR]

In this paper, we present a laser monitor with two image acquisition channels based on two brightness amplifiers and two digital cameras that allows visualizing 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 allows studying the surface of samples of powder materials during high-temperature combustion accompanied by intense glow and scattering of combustion products. The use of two-channel visualization allows studying the surface of a burning sample in more detail—in particular, studying the inhomogeneity of the combustion process. [ABSTRACT FROM AUTHOR]

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.

This paper presents the results of real-time monitoring of air combustion of aluminum nanopowder and its mixtures with aluminum micropowder and iron oxide III. An optical system with a brightness amplifier was used along with visual monitoring to characterize the reflectivity of the sample surface. The reflectivity was analyzed after registering by a photodiode the intensity of radiation reflected from the surface and then amplified by the brightness amplifier at 510.6- and 578.2-nm wavelengths. Analysis of the images obtained with a high-speed camera and the photodiode output oscillograms showed that the intensity of the brightness amplifier output corresponds to the main stages of the combustion process, including the beginning of combustion, spreading of the heat wave and rise of the second combustion wave. The proposed technique is adequate for real-time monitoring of the combustion process with temperatures of 2200 °C–2400 °C, which is accompanied by intensive lighting. [ABSTRACT FROM AUTHOR]

The influence of the brightness amplifier operation mode on images formed with a bistatic laser monitor is studied. The bistatic laser monitor is an active optical system with two active elements. A possibility of imaging remote (to more than 5 m) objects with this instrument is evaluated. It is shown that a change in the concentration of active substance (copper bromide) of the amplifier significantly affects the amplification of the input signal. The active substance temperature rise from 480 to 550°C increases the gain throughout the input signal range. A further increase in the temperature (up to 570°C) increases the gain only at a relatively weak input signal (less than 100 mW). The resulting amplification characteristics of the active optical system are described and compared with the parameters of images formed (distortion and brightness). [ABSTRACT FROM AUTHOR]

Abstract This paper addresses the theoretical study of the spatio-temporal gain profile of the copper vapor active media. The description of a kinetic model of a copper vapor amplifier which allows us to study spatio-temporal evolution of the amplifying characteristics is described. Using the kinetic model time and radial evolution of the medium optical gain and factors which governs the radial gain profile inhomogeneity of the brightness amplifier are shown. [ABSTRACT FROM AUTHOR]

Abstract This study focused on the synthesis of aluminium nitride (AlN) by combusting aluminium nanopowder in air. To investigate the combustion of aluminium nanopowder, a copper bromide laser monitor was used. The optical system equipped with brightness amplification allowed the elimination of the background lighting effect and enabled the high time-resolved recording of the process. In particular, the laser monitor enabled us to detect changes in the morphology and optical properties of the surface of the aluminium nanopowder sample as well as to observe the propagation of the combustion waves in spite of the intense background lighting during combustion. The main time parameters of the combustion of aluminium nanopowder in air were determined. To improve and facilitate the processing of laser monitored high-speed video recordings, we proposed to analyse the time dependence of the intensity of the output signal of the laser monitor. The dependence was used to successfully detect the occurrences of all combustion waves and describe their dynamics. The time dependence also favourably represented the evolution of the reflection coefficient of the combustion products of aluminium nanopowder. This is the first time that this property of aluminium nanopowder has been investigated. The reflection coefficient evolution coupled with video recordings of the sample surface development during the combustion of nanopowder could be used to control the combustion process. [ABSTRACT FROM AUTHOR]

Results of the experimental study of two high-frequency active elements of different sizes of a CuBr laser operating in the generator, single-pass amplification, and superradiance modes are presented. A pulse repetition rate of 195 kHz is attained for the first time in the supperradiance mode. Using the method of express estimation of the radial profile, it is shown that the gain profile does not change significantly throughout a wide pulse repetition rate range (up to 195 kHz) in the case of a small-diameter active element. [ABSTRACT FROM AUTHOR]

The methods for real-time visual diagnostics of high-speed processes of materials modification and production are presented. The main problem of visualization of such processes is the intense glare which blocks the investigated area. To decrease the negative effect of the glare (high intensive background light) the copper bromide vapor brightness amplifier is used. It has been shown that the imaging method with a brightness amplifier proposed in this paper proves to be the most reliable to obtain the information about objects or processes in a real time mode using high frequency copper bromide vapor brightness amplifier. The results of visualization of different processes, including nanoparticles production, are presented. The benefits and limitations of both methods used for imaging have been also demonstrated. [ABSTRACT FROM AUTHOR]

This paper addresses the experimental study of the beam profile of the CuBr brightness amplifier operating at a wide range of pulse repetition frequencies. The use of a medium-size gas discharge tube (2 cm) ensures the operation of the brightness amplifier both at typical PRFs (520 kHz) and at higher PRFs (up to 100 kHz), either with or without HBr additive. The effect of the active additive on the beam profile is demonstrated. The testing results on kinetic modeling of radial processes in the laser (brightness amplifier) plasma are also discussed. [ABSTRACT FROM AUTHOR]

The paper presents a laser monitor with 10 μs time-resolution based on a high-frequency copper bromide vapor brightness amplifier. A sync circuit has been designed for single-pulse imaging. The analysis of amplifying characteristics of the active elements and active optical system (laser monitor) parameters allowed to determine the optimal concentration of HBr at which the images can be obtained with minimum distortions. For the active element operating at high frequencies (more than 50 kHz) as a brightness amplifier, the concentration of HBr must be lower than that needed for obtaining the maximum output power. The limiting brightness temperature of the background radiation which does not affect the image quality is determined. The potential feasibility of using a proposed brightness amplifier for visualizing processes blocked from viewing by the background radiation with the brightness temperature up to 8000 K is demonstrated. [ABSTRACT FROM AUTHOR]

Gas-dynamic processes that run in pulse-periodic discharges initiated by runaway electrons in atmospheric pressure air are studied with CuBr-laser based laser monitor and schlieren method. Voltage pulses ( U = 13 kV, FWHM is 10 ns, front length is 4 ns, negative polarity, f = 60-3200 Hz) applied to a coneshaped copper cathode with cone base diameter, apex angle, and corner radius of cone vertex of 6 mm, 30°, and 0.2 mm, respectively. A flat copper anode was located at a distance of 2 mm from the cathode. It is established that discharge plasma products with copper vapors are carried in a radial direction along the anode surface to a distance of 24 mm for 2.5 ms. The temperature of the gas heated is ~1 × 10 K. It is shown that the use of the laser monitor in transmitted light provides for contrast images of optical inhomogeneities that appear in gas discharges. [ABSTRACT FROM AUTHOR]

The paper presents first results on the use of a CuBr laser for high-speed imaging of the process of nanomaterial synthesis. Various imaging circuits are considered. A possibility of full suppression of stray background light, which is the laser monitor main advantage for diagnostics, is shown. The application areas for each circuit are discussed. [ABSTRACT FROM AUTHOR]

Frequency and energy characteristics of a MnBr vapor laser with a built-in reactor, i.e., with gas vapors being produced within a gas discharge tube, and the dependence of the average output power on different parameters are studied in this work. The values of the GDT wall temperature and buffer gas pressure required for obtaining the maximum output power are determined. It is shown that active media of this kind are as good as media with a conventional method of gas vapor production. A pulse repetition frequency of 100 kHz is attained for the first time for a medium on Mn atom transitions. The use of this active medium as a brightness amplifier in active optical systems is described; the amplifying characteristics are analyzed. [ABSTRACT FROM AUTHOR]

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. • The dependence of the CuBr brightness amplifier gain on the input signal level is determined. • 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. • The minimal level of input signal required to form the image with a contrast sufficient for mathematical processing is 1.4% of ASE power. [ABSTRACT FROM AUTHOR]

This paper presents the theoretical study of the optical gain of copper vapor active media for a wide range of input signal power. The modified kinetic model is used to identify the effect of the optical saturation on the amplified spontaneous emission and the spatio-temporal evolution of amplifying characteristics. Also, the dependence of these characteristics on the copper concentration is studied. The results obtained are discussed in the context of using copper vapor active media in laser monitors. [ABSTRACT FROM AUTHOR]

• CuBr-laser monitor is used for imaging a growing diamond crystal in microwave plasma of CVD reactor. • Contrast images of diamond surface through H 2 -CH 4 plasma background radiation. • The optical configuration provides 4 × 4 mm2 field of view with spatial resolution up to 30 µm. We used an active optical system referred to as 'laser monitor' based on a copper bromide vapor brightness amplifier for imaging a diamond crystal surface during its synthesis in a microwave plasma in CH 4 -H 2 gas mixture. The approach allows observation of an entire crystal without interrupting the chemical vapor deposition process. It is demonstrated that the broadband plasma background radiation with the brightness temperature of about 3000 K does not interfere with object real-time monitoring at the laser wavelength of 510.6 nm. High quality images obtained using both passive (laser illumination) and active (laser monitor) methods provide information about the surface relief of the growing crystal with resolution of a few tens of micrometer. Each frame is formed through one pulse (about 30 ns), with the maximum frame rate being 20,000 frames/sec. [ABSTRACT FROM AUTHOR]