An improved method for determining the temperature of a laser diode and the thermal resistance of the main elements of an equivalent thermal circuit based on measuring the transient temperature-sensitive characteristics of the forward voltage at the p-n junction in response to a step-like effect of a heating current pulse was proposed. The individual components and the total thermal resistance of the laser diode were experimentally studied and analyzed. It was found that the main contribution to the total thermal resistance, which was similar to 7.4 K/W, was made by the laser crystal layer itself from the p-n junction to the lower plane (similar to 2.8 K/W) and the AlN-switching thermally conductive substrate (similar to 2.6 K/W), for which no further reduction paths were visible. It was shown that a continuous mode of operation was realized without significant overheating Delta T < 40 K with the threshold I approximate to 2 A exceeded by six times, generation power P approximate to 2.5 W, efficiency similar to 30%, and differential quantum output eta approximate to 60%.

В ходе одного из важнейших процессов круговорота углерода в биосфере – фотосинтеза, происходят не только фотохимические и биохимические реакции, но и изотопное фракционирование основных биогенов и других элементов. Условия минерального питания, факторы влаго- и теплообеспеченности, видовые и сортовые особенности, световые условия при фотосинтезе влияют не только на его интенсивность, но и определяют изотопный состав ряда метаболитов, в том числе в зависимости от специфики растений по типу фиксации углерода (C3-, C4-, CAM- пути), чем и обоснован выбор объектов исследования – пшеница яровая (Triticum aestivum L.), как классический представитель C3- пути фиксации углерода и амарант (Amaranthus hopochondriacus L.), как классический представитель C4- культуры. Исследование изотопного состава метаболитов в целом, и углерода метаболитов в особенности, позволяют раскрыть физические и физиолого-биохимические механизмы протекания важнейших процессов в растениях. В настоящее время наиболее развитыми методами являются радиоизотопные исследования и методы с использованием масс-спектрометрии стабильных изотопов, требующие особых условий работы и сложной подготовки такой как: общее разложение проб (твердофазное окисление), методы хроматографии и другие. Нами предложен и апробирован ранее метод метаболизацации растворимых метаболитов с использованием культуры Saccharomyces cerevisiae в качестве альтернативного для последующей изотопной масс-спектрометрии – биологический метод пробоподготовки. Данный метод показал свою применимость для подготовки растительных проб к изотопному анализу углерода, а отсутствие фоторецепторных систем позволяет использовать Saccharomyces cerevisiae для определения влияния спектрального состава света на изменение изотопного состава углерода метаболитов растения. Инкубирование дрожжей с растительной пробой в прозрачной камере дает возможность облучать фотосинтезирующие листья растений, переводить углеводы растения в углекислый газ и отбирать пробы для масс-спектрометрических исследований изотопного состава углерода одновременно в динамике, когда как метод твердофазного окисления не позволяет исследовать нативные пробы при изменении факторов внешней среды. В работе показано влияние световых условий на фракционирование изотопов углерода листьями растений с различным типом фотосинтеза. С применением биологического метода подготовки проб в условиях динамического измерения состава метаболических газов определены и оценены скорости изменения изотопного отношения углерода 13С/12С в зависимости от спектральных характеристик освещения. Выявлено более значительное обогащение изотопом 13С листьев растений пшеницы с С3-типом фотосинтеза при облучении синим светом и листьев амаранта с С4-типом фотосинтеза при воздействии красным светом по сравнению с другими областями спектра.

The energy and spectral characteristics of the most powerful AlInGaN LEDs with emission spectrum peaks at wavelengths of 440, 470, and 510 nm were studied in relation to the pumping of two laser media: Ti:Sapphire (Ti:Al2O3) and alexandrite (Cr:Al2BeO4). The absorption coefficients of the LED radiation in the laser media were studied experimentally with respect to the peak wavelength, operating mode, and excitation level. The corresponding spectral matching values (the efficiency of absorption of the pump radiation) were calculated for various combinations of the LEDs and active laser media. The energy characteristics (radiation power, pulse energy) of the LED emitters were studied over a wide range of excitation levels. The maximum energy capabilities of the LED emitters were assessed in terms of both output optical power and efficiency. The optimum combinations of LEDs and active laser media to achieve laser generation were determined.

High-power AlGaInN LEDs are of interest for pumping of dyes lasers. In this regard, comprehensive studies of the power and spectral characteristics of LEDs in short-pulse modes used to laser pump were carried out. The energy capabilities and spectral properties of LED excitation of coumarin dyes were revealed.

The work is devoted to the creation and study of high-power AlGaInN LED source with emission wavelengths (460–480) nm for pumping of solid-state lasers. The electrical, spectral, power and thermal characteristics were studied in a wide range of currents, continuous and pulsed modes. The design of LED matrices, which provides a tight “packing” of LEDs, their electrical commutation, efficient heat removal and a power supply for a wide pulse range has been proposed. The developed emitter comprises the most powerful and efficient to date LE Q8W (Osram) LEDs and is intended primarily for pumping Ti:Sapphire laser, the absorption band of which is well matched with the emission spectrum of the used LEDs. The achieved optical pumping power density in the pulsed mode is ~25 W/mm2, which corresponds to the lasing threshold.

Introduction. Diseases accompanied by a violation of the blood supply to the intestinal wall occupy one of the main places in urgent surgery of the abdominal organs. Intraoperative assessment of intestinal viability is one of the most difficult tasks and plays a leading role in determining the volume of surgical aid, predicting the course of the postoperative period.Aim. To study the possibility of using contrast imaging using a controlled polychrome LED light source to assess the viability of the intestinal wall of a model animal in conditions of acute ischemia.Materials and methods. The work is based on the results of experimental studies conducted on 15 clinically healthy sexually mature laboratory rats. The simulation of acute small intestine ischemia lasting from 15 minutes to 12 hours was performed by ligation of the major vessels. Each animal underwent a relaparotomy after a corresponding time interval. The intestine was extracted from the abdominal cavity and visual parameters of wall necrosis were assessed using the Kerte method and using a polychrome LED light source for contrast imaging of biological tissues during surgery. After determining the visual signs of necrosis, intestinal fragments were submitted for pathomorphologic examination. The study was ended by removing the animal from the experiment according to the protocol approved by the Ethics Committee.Results. The spectral composition of the light source providing the most reliable detection of necrosis of the intestinal wall is represented by two spectral bands with maximum wavelengths of peak = 503 nm, peak = 594 nm and an approximate ratio of band intensities of 2:1. By morphological study, the following intervals were found to be significant when simulating small intestinal ischemia in the experiment: 1 hour after ligation - time of onset of ischemia, 6 hours - time when ischemia is reversible, and 12 hours - time when small intestine necrosis is recorded. Conclusions. The use of a controlled shadowless semiconductor light source for contrast imaging of biological tissues during surgery in the selected mode improves the definition of visual parameters of intestinal viability.

The object of study in this work was the most advanced AlInGaN LEDs of the “UX:3” design with a distributed system of reflective contacts located on the back side of the emitting chip. The current dependences of the output optical power and emission spectral characteristics, including their distribution (mapping) over the emitting surface, in a wide range of operating currents up to ~ 30A have been studied. An analysis of the near-field emission by intensity and spectrum revealed a high uniformity of the current density distribution at all levels of excitation (no current crowding). Thus, the saturation of the optical power and the quantum efficiency droop are explained by purely internal factors, which are well described by the ABC-model.

High-power AlGaInN LEDs are of interest for pumping of Ti-sapphire lasers. In this regard, comprehensive studies of the power and spectral’ characteristics of LEDs in short-pulse modes used to laser pump were carried out. The energy capabilities and spectral properties of LED excitation of Ti-Sapphire were revealed. Designs of LED arrays and a laser head have been developed, the distribution of pumping in the active element have been simulated.

The design and operation of a small-sized LED-based device for psychophysiological express diagnostics of functional states is considered. Diagnostics of functional states is carried out using dihaploscopic techniques for measuring the critical frequency of flicker fusion. The construction of the device includes a tablet computer with software for select, conFigure and run tests and a virtual reality glasses with LED matrix forming the color and shape of the test signal.

The electroluminescent characteristics of powerful AlInGaN LEDs in the regime of high-pulsed current are investigated. The current dependencies of power and emission spectra of blue-green LEDs are established in their relationship with the efficiency of active medium Ti:Sapphire pumping. The reached values of the optical pumping power density using LEDs are estimated.

Comprehensive analysis of current spreading, temperature distribution and near field electroluminescence of high-power "UX:3" AlInGaN emitting chips with a distributed system of reflective contacts, located on the back of the chip, has been performed by combination of different experimental methods. Current dependences of power and spectral characteristics, including their distribution (mapping) over the emitting surface, were studied in a wide range of operating currents. A thermal resistance evaluation was based on transient electrical processes under heating by direct current and analysis of thermal equivalent circuit (the Cauer's model). The high resolution mapping of electroluminance and thermal radiation was obtained by optical microscope and infrared images technique. It has been established distribution pattern of light and temperature at different levels of excitation. The conclusions were drawn about the degree of uniformity of the current and light spreading and their influence on the power characteristics of devices.

The object of study in this work was the most advanced AlInGaN LEDs of the "UX : 3" design with a distributed system of reflective contacts located on the back side of the emitting chip. The current dependences of the output optical power and emission spectral characteristics, including their distribution (mapping) over the emitting surface in a wide range of operating currents up to ~ 30 A have been studied. An analysis of the near-field emission by intensity and spectrum revealed a high uniformity of the current density distribution at all levels of excitation (no current crowding). Thus, the saturation of the optical power and the quantum efficiency droop are explained by purely internal factors, which are well described by the ABC model. Keywords: AlInGaN LED, quantum efficiency, emission spectrum, near-field emission.

The AlInGaN LEDs of the UX:3 design with a distributed system of reflective contacts located on the emitting crystal back, which are most advanced to date, are studied. The current dependences of power and spectral characteristics including their mapping over the radiating surface in a wide range of operating currents up to ~30 A have been investigated. Analysis of the radiation near-field according to intensity and spectrum has revealed a high uniformity of the current density at all levels of excitation (no crowding effect). The optical power saturation and the drop in quantum efficiency have been explained using only internal factors, which are well described by the ABC model.

The goal of the study is examination of current-crowding effect in high power AlInGaN LEDs. This effect was presented by mapping of EL (electroluminescence) near filed under high pulse current. LED chip of vertical design was study in high range of current (10 −9 ÷ 70A). This operating mode of LEDs are interesting for different applications, such as pumping lasers, VLC and LiFi, as well as for investigation accelerated degradation process of LEDs.

LEDs operating under high pulsed current are of a great interest for different applications, in particular, for VLC (LiFi) systems and laser pumping. Current dependences of the efficiency and emission spectra as well as the rise and fall times of high-power blue LEDs were investigated under extremely high pulse current density up to 7 kA/cm2 and pulse duration from 100 ns to 3 μs. Analysis of the pulse behaviour of the LEDs reveals that the main droop in the efficiency and change in spectra occur up to the current densities ~ 1 kA/cm2 and seems to be non-thermal.

LEDs operating under high pulsed current density, which excludes self-heating, are of great interest for different applications, in particular, for pumping lasers with a short time of activator relaxation, such as Ti:Sapphire. The current dependences of the efficiency emission spectra as well as the rise and fall times of high-power blue and green LEDs were investigated under extremely high pulse current density up to 7 kA/cm 2 and a pulse duration of 100 ns to 3 μs. An analysis of the pulse behaviour of the LEDs reveals that the main droop in efficiency and a change in the spectrum occur up to the current densities ∼ 1 kA/cm 2 and seem to be non-thermal. The energy and spectral pulse characteristics of the radiation were studied with simultaneous recording the excited Ti:Sapphire photoluminescence in order to determine the optimal pumping conditions.

The article reviews the main theoretical, engineering and technological, circuit-engineering and software aspects of development of a dynamically controlled luminaire based on light emitting diodes for contrast visualisation of biological tissues during surgical procedures. The design concept of such surgical luminaire is proposed, which combines high-quality white lighting and coloured accent lighting increasing the contrast of visualisation of particular tissues and borders between them. The calculation model of the luminaire optical system allows maximising the level of illumination and uniformity of illuminance and colour of the surgical area. The software of the luminaire allows to independently modifying intensity of radiation of six coloured light emitting diodes with blue (460 nm), turquoise (505 nm), green (530 nm), green-yellow (550 nm), orange (590 nm) and red (630 nm) light colours for synthesis of coloured lighting of virtually any chromaticity. The level of general lighting by means of phosphor light emitting diodes can also be varied within a wide range. Chromaticity and level of lighting are adjusted by means of pulse-duration modulation of light emitting diode current and the light parameters of the luminaire are controlled by a remote computer via a radio channel. This medical luminaire is primarily designed for lighting during surgical procedures and it can also be used for visual diagnostics based on the colour of analysed tissues.

The theoretical, design, technological and software aspects of creating a dynamically controlled LED surgical lamp for contrast visualization of biological tissues during surgical operations are considered. The concept of design a surgical lamp, which combines white light illumination and dynamic control colored illumination, is proposed. It allowed both to reach high-quality illumination of the operational field and to improve the contrast of visualization of different biological tissues and objects. An optical system of the lamp, which allows achieving maximum and uniform illumination and provides uniform color mixing all over the operating field, is considered. Surgical lamp used both phosphor-conversion white LEDs for general illumination and monochrome AlInGaN, AlGaInP LEDs for precision control of color illumination. The developed software allows you to independently change the intensity of six spectral LED components: blue (460 nm), cian (505 nm), green (530 nm), lime (550 nm), orange (590 nm) and red (630 nm) to synthesize colored lighting in wide chromaticity scale. Also, within a wide range, it is possible to change the luminance and color temperature of the general illumination from white phosphor LEDs. Color and luminance evels are controlled by pulse-width modulation of the LED current. The light parameters of the surgical lamp are set by remote computer connected to the lamp via Bluetooth. To determine optimum illumination conditions for contrast visualization, optical characteristics of different biological tissues in combination with color LED emission are investigated. As a result, the experiments on animals showed the contrast of biological tissues imaging increases when they were illuminated with specially selected spectra emitted by developed lamp.

Current dependences efficiency, emission spectra, rise and fall time of 3 different design high-power blue LEDs have been investigated under extremely high pump current density up to 7 kA/cm 2 and pulse duration 100 ns. Analysis of the pulse-behavior of the LEDs reveals revealed that the main droop in efficiency and a change in the spectrum occurs up to current densities of ~2kA/cm 2 and have a non-thermal character. The rise and fall time are more than 20 ns due to the high capacitance of the LEDs.