Method development to secure the stability of the parameters of pulsed and continuous radiation in laser systems with semiconductor pumping

The necessity of increasing the stability of the parameters of pulsed and cw laser radiation when operating at peak powers is substantiated. Particular attention is paid to the parameters of pulsed laser radiation in systems with semiconductor pumping. The main requirement in this case is the repeatability of the parameters of the output pulses with high accuracy. This condition is ensured by the stability of the diode supply drivers, especially at peak powers, which are required for scientific research. It was found that even a short-term excess (about 1 ms) of the upper range of the permissible current leads to damage to the laser diode, which instantly degrades the parameters of laser radiation. The developed technique can significantly reduce the likelihood of these phenomena and increase the reliability of the laser.

Assessment of Radiation Risk on Healthcare Workers and Public in & around Two Largest Hospital Campuses of Bangladesh

Ionizing radiation gives tremendous benefit to mankind in the hospital through diagnosis and treatment to patients but unnecessary radiation may cause harm to healthcare workers & the public. The purpose of the study is to continuous radiation monitoring in & around the three largest radiological facilities of Bangladesh such as Atomic Energy Centre Dhaka (AECD), Dhaka Medical College Hospital (DMCH) & Bangabandhu Sheikh Mujib Medical University (BSMMU) campuses, and estimation of radiation risk on healthcare workers & public health. Continuous radiation monitoring was performed in & around the AECD, DMCH, BSMMU campuses from August-October 2020 using the Chemiluminescent Dosimeters. The yearly effective doses to healthcare workers and the public due to radiation released from the facilities were ranged from 0.606 ± 0.031 mSv to 0.801 ± 0.0.042 mSv with a mean of 0.707 ± 0.053 mSv. The excess lifetime cancer risk (ELCR) on healthcare workers & public health were evaluated based on the yearly effective dose and ranged from 2.486 Χ 10-3 to 3.287 Χ 10-3 with a mean of 2.900 Χ 10-3. The average yearly effective dose and ELCR on healthcare workers & public health were lower than those of the worldwide permissible values. Continuous radiation monitoring in & around the largest radiological facilities is required for detection of the radiation generating equipment’s malfunctions and improper handling of the radioactive materials. The study would help for minimization of radiation risk on healthcare workers & the public and this keeps the hospital’s environment free from radiation hazard.

Justification of requirements for digital signal synthesizers for various types of radar

В работе обосновываются требования к уровню искажений радиолокационных станций с импульсным и квазинепрерывным излучением, построенных на основе цифровых синтезаторов сигналов четырех типов: цифровых синтезаторах отсчетов напряжения и цифровых синтезаторах отсчетов фазы с равномерной дискретизацией, цифровых синтезаторах отсчетов напряжения и цифровых синтезаторах отсчетов фазы с неравномерной дискретизацией. При построении задающего устройства РЛС возникает вопрос о выборе типа цифрового синтезатора сигналов. Основными исходными критериями при этом являются максимальный рабочий диапазон цифрового синтезатора и уровень внутриполосных искажений. При выборе типа цифрового синтезатора сигналов необходимо учитывать большое количество факторов, основными из которых являются сложность исполнения формирователя цифровых отсчетов, возможность реализации формирователя цифровых отсчетов с требуемым быстродействием и количеством разрядов [1, 2]. При предъявлении требований к суммарному уровню искажений используется критерий допустимого снижения вероятности правильного обнаружения по сравнению с её потенциальным значением при фиксированной вероятности ложной тревоги. Исходя из данного критерия в импульсных РЛС максимальное относительное среднеквадратическое значение искажений взаимокорреляционной функции сигнала с угловой модуляцией, формируемого цифровым синтезатором, не должно превышать $D_{\\delta x}\\le $-(51...67) дБ. В РЛС с квазинепрерывным излучением максимальное относительное среднеквадратическое значение искажений автокорреляционной функции сигнала с угловой модуляцией не должно превышать $D_{\\delta }\\le $-(80...120) дБ. Количество разрядов квантования фазы, напряжения и компенсации временной задержки в цифровых синтезаторах сигналов зависит не только от максимального относительного среднеквадратического значения искажений взаимокорреляционной функции но и от количества отсчетов сигнала с угловой модуляцией. Поэтому первоначально необходимо выбрать эталонную частоту цифрового синтезатора сигналов, задаваясь видом модуляции и эффективной шириной спектра сигнала с угловой модуляцией исходя из ТТХ РЛС. The paper substantiates the requirements for the level of distortion of radar stations with pulsed and quasi-continuous radiation, built on the basis of digital signal synthesizers of four types: digital synthesizers of voltage counts and digital synthesizers of phase counts with uniform sampling, digital synthesizers of voltage counts and digital synthesizers of phase counts with uneven sampling. When building a radar master device, the question arises about choosing the type of digital signal synthesizer. The main initial criteria are the maximum operating range of the digital synthesizer and the level of in-band distortion. When choosing the type of digital signal synthesizer, you must take into account a large number of factors, the main of which are the complexity of the execution of the digital readout shaper, the possibility of implementing a digital readout shaper with the required speed and number of digits [1, 2]. When making requirements for the total level of distortion, the criterion of acceptable reduction of the probability of correct detection in comparison with its potential value for a fixed probability of false alarm is used. Based on this criterion, in pulse radars, the maximum relative RMS value of the distortion of the intercorrelation function of a signal with angular modulation generated by a digital synthesizer should not exceed $D_{\\delta x}\\le $-(51...67) dB. In a radar with quasi-continuous radiation, the maximum relative mean-square value of the distortion of the autocorrelation function of the signal with angular modulation should not exceed $D_{\\delta }\\le $- (80...120) dB. The number of bits of phase quantization, voltage and time delay compensation in digital signal synthesizers depends not only on the maximum relative RMS value of the distortion of the intercorrelation function, but also on the number of samples of the signal with angular modulation. Therefore, initially you need to select the reference frequency of the digital signal synthesizer, setting the type of modulation and the effective spectrum width of the signal with angular modulation based on the tactical and technical characteristics radar.

Nanosecond laser-induced breakdown assisted by femtosecond laser pre-ionization in air: the effect on spatial resolution and continuous radiation

Laser-induced breakdown spectroscopy (LIBS) is a powerful technique for quantitative diagnostics of gases. The spatial resolution of LIBS, however, is limited by the volume of plasma. Here femtosecond-nanosecond dual-pulsed LIBS was demonstrated. Using this method, the breakdown threshold was reduced by 80%, and decay of continuous radiation was shortened. In addition, the volume of the plasma was shrunk by 85% and hence, the spatial resolution of LIBS was significantly improved.

Requirements Justification to Digital Signal Synthesizers for Various Types of Radar Systems

The paper justifies the requirements for the level of distortion of radar stations with pulse and quasi-continuous radiation, built on the basis of digital signal synthesizers of four types: digital synthesizers of voltage counts and digital synthesizers of phase counts with uniform sampling, digital synthesizers of voltage counts and digital synthesizers of phase counts with uneven sampling. When building a radar master device, the question arises about choosing the type of digital signal synthesizer. The main initial criteria are the maximum operating range of the digital synthesizer and the level of in-band distortion. When choosing the type of digital signal synthesizer, you have to take into account a large number of factors, the main of which are the complexity of the execution of the digital readout shaper, the possibility of implementing a digital readout shaper with the required speed and number of digits [1, 2]. When making requirements for the total level of distortion, the criterion of acceptable reduction of the probability of correct detection in comparison with its potential value for a fixed probability of false alarm is used. Based on this criterion, in pulse radars, the maximum relative RMS value of the distortion of the intercorrelation function of a signal with angular modulation generated by a digital synthesizer should not exceed Dδx ≤ –(51...67) dB. In a radar with quasi-continuous radiation, the maximum relative mean-square value of the distortion of the autocorrelation function of the signal with angular modulation should not exceed Dδ ≤ –(80...120) dB. The number of bits of phase quantization, voltage and time delay compensation in digital signal synthesizers depends not only on the maximum relative RMS value of the distortion of the intercorrelation function, but also on the number of samples of the signal with angular modulation. Therefore, initially you need to select the reference frequency of the digital signal synthesizer, setting the type of modulation and the effective spectrum width of the signal with angular modulation based on the tactical and technical characteristics radar

Formation of radiation-disturbed layer in Al/SiO2/n-Si structures irradiated by helium ions with energy 5 MeV

This paper focuses on researching the change in the volt-farad characteristic of the Al/SiO2/n-Si structure irradiated by helium ions with the energy of 5 MeV in different frequencies of 1 kHz; 10 kHz; 100 kHz and 1 MHz. The voltage dependence of the capacitance and the frequency dependence of the dissolution angle are measured by LCR Agilent E4980A and Agilent 4285A meter. The complex electrical module’s hodograph of irradiated structure shows that there is a formation of quasi-continuous radiation-disturbed layer at fluence 1012 cm-2 with U < -7 V and at 1013 cm-2 with U < -20 V, which enhances the speed of charged particles, thereby increasing the reverse current in the irradiated structure.

Determination of the profile of the temperature field of material heated by continuous laser radiation

Spectral pyrometry was used to determine the surface temperature distribution of Si, Nb, Cu, and graphite samples when they were locally heated by continuous radiation of an Nd:YAG laser (λ = 1.064 μm). With prolonged exposure to radiation, a stationary temperature field was established in the samples. The thermal spectra were recorded with a small spectrometer in the visible range in the temperature range above 850 K. The optical fiber used to transmit the radiation spectrum to the spectrometer had an additional diaphragm with a diameter of 1 mm located at a certain distance from the fiber end, which ensured the locality of the recorded spectra. The optical fiber moved continuously along the sample, and the spectrometer recorded up to 100 spectra with a frequency of 5-10 Hz. The temperature profile of the samples was calculated based on the results of processing the spectra using the Spectral Pyrometry program.