Light Pulse Energy Research Articles

Effect of annealing temperature on the optoelectrical synapse behaviors of A-ZnO microtube

Optoelectronic synapses with fast response, low power consumption, and memory function hold great potential in the future of artificial intelligence technologies. Herein, a strategy of annealing in oxygen ambient at different temperatures is presented to improve the optoelectronic synaptic behaviors of acceptor-rich ZnO (A-ZnO) microtubes. The basic synaptic functions of as-grown and annealed A-ZnO microtubes including excitatory postsynaptic current (EPSC), short-term memory (STM) to long-term memory (LTM) conversion, and paired-pulse facilitation (PPF), were successfully emulated. The results show that the annealing temperature of 600 °C yields high figures of merit compared to other annealed A-ZnO microtubes. The 4-fold and 20-fold enhancement dependent on the light pulse duration time and energy density have been achieved in the 600 °C annealed A-ZnO microtube, respectively. Furthermore, the device exhibited a PPF index of up to 238% and achieved four cycles of “learning-forgetting” process, proving its capability for optical information storage. The free exciton (FX) and donor–acceptor pair (DAP) concentrations significantly influenced the persistent photoconductivity (PPC) behavior of A-ZnO microtubes. Therefore, the LTM response can be controlled by the adjustment of numbers, powers, and interval time of the optical stimulation. This work outlines a strategy to improve the EPSC response through defect control, representing a step towards applications in the field of optoelectronic synaptic device.

Оцінка наслідків застосування тактичної ядерної зброї на населення та інфраструктуру в районах ядерного вибуху

The article analyzes the process of formation and establishes the characteristics of the striking factors of a nuclear explosion of tactical nuclear ammunition with a power of 0.1 to 10 kt when damaging military facilities and the accompanying damage to the population of civilian communities and personnel of infrastructure facilities. Calculated are data on the parameters of air shock wave action zones, penetrating radiation flow, light pulse energy beam flow, and the dimensions of the zone of radioactive contamination of the area, which can create a negative impact on the population, residential buildings, personnel, and critical infrastructure facilities in the area of application of tactical nuclear weapons. It is shown that the zone affected by an air shock wave, depending on the type of explosion of tactical nuclear ammunition and its power, can reach a radius of up to 3100 m. Dangerous light pulse damage to the population and personnel located in the open area will be observed at a distance of 440 to 3700 m from the epicenter of the nuclear explosion. The negative impact of the penetrating radiation of a nuclear explosion on the population and personnel of critical infrastructure facilities will be observed at distances from 560 to 1300 m, depending on the type of explosion and the power of the tactical nuclear ammunition. The dimensions of the zone of radioactive contamination, in the case of the explosion of tactical nuclear ammunition, in which the most severe degree of radiation damage to the population and personnel of critical infrastructure objects will be observed, with their open location in the area, depending on the power and type of explosion, can reach from 1400 to 2600 m. And the zone in which it is necessary to carry out the priority immediate evacuation of the population can be from 3.4 to 44.0 km in the direction of the average wind. It was determined that the scale of radioactive contamination of the area will have the greatest values of the size of the areas of negative impact relative to other types of impressive factors of the nuclear explosion of tactical nuclear ammunition. In large areas of the regions adjacent to the area of application of the specified ammunition, a significant negative radiation effect will be created, which will require measures of radiation protection and evacuation of the population.

Nanomotion of Micro-Objects Driven by Light-Induced Elastic Waves on Solid Interfaces

It has been recently reported that elastic waves induced by nanosecond light pulses can be used to drive nanomotion of micro-objects on frictional solid interfaces, a challenging task for traditional techniques using tiny optical force. In this technique, the main physical quantities and parameters involved are temporal width and energy of light pulses, thermal heating and cooling time, friction force, and elastic waves. Despite a few experimental observations based on microfiber systems, a microscopic theory, which reveals how these quantities collaboratively enable motion of the micro-objects and derives what the underlying manipulation principles emerge, is absent. In this paper, a comprehensive theoretical analysis---centralized around the above listed physical quantities, and illuminated by a single-friction-point model in conjunction with numerical simulations---is established to pedagogically clarify the physics. Our results reveal the two essential factors in this technique: (1) the use of short light pulses for rapid thermal expansion overwhelming friction resistance and (2) the timescale asymmetry in thermal heating and cooling for accumulating a net sliding distance. Moreover, we examine the effects of spatially distributed friction beyond the single-friction-point consideration, and show ``tug-of-war''-like friction stretching in the driving process. Given these insights, we positively predict that this elastic-wave-based manipulation principle could be directly translated to micro- and nanoscale optical waveguides on optical chips, and propose a practical design. We wish that these results offer theoretical guidelines for ongoing efforts of optical manipulation on solid interfaces with light-induced elastic waves.

Passively Q-switched microchip laser based picosecond light source in the visible-red to near-infrared band for semiconductor excitation.

We developed a visible-red to near-infrared wavelength tunable all-solid-state laser system utilizing an optical parametric generation process in a MgO doped PPLN crystal pumped at 532 nm by an amplified and frequency doubled picosecond passively Q-switched Nd:YVO4 microchip laser. A broad bandwidth, tuneable over 300 nm between 710 nm to 1015 nm, is accessible. Depending on the green pump light pulse energy, pulses with durations down to 69 ps as well as pulses with energies above 2 µJ were achieved with kHz repetition rates.

Portable coherent Doppler light detection and ranging for boundary-layer wind sensing

We present the performance of the portable wind light detection and ranging (LIDAR) system based on the 1.55-μm all-fiber technology in the atmospheric boundary layer. The LIDAR is 23.9 kg in weight, 50 cm in height, 35 cm in width, and 27 cm in depth, and the system’s local oscillator (LO) light power, pulse energy, and pulse width are adjustable. The LO light power is optimized to 3 mW, to minimize the effect of the relative intensity noise. The transmitting pulse energy is reduced to 19 μJ, to minimize the system’s power consumption while covering a detection height of >1 km in clear-sky condition. The pulse width is variable from 100 to 400 ns corresponding to a minimum resolution from 15 to 60 m. The signal-to-noise ratio performance experiment shows that this system can detect as high as 2.1 km. Field experiments compared with radiosonde and anemometer show that this system presents a detection accuracy of better than 1 m / s and 10 deg.

Crystallisation behaviour of CH3NH3PbI3 films: The benefits of sub-second flash lamp annealing

Crystallisation of the spin-coated hybrid perovskite films has some basic issues restraining the up-scaling of this technology. The reason consists in substantial chemical impact of the solvent during drying that lessens control of crystallisation and reproducibility. This current investigation proposes very fast crystallisation by means of a flash lamp to solve those issues. CH3NH3PbI3 films were prepared on glass and silicon substrates by spin-coating from N,N-dimethylformamide based solutions with various CH3NH3I to PbI2 ratios (1:1, 2:1 and 3:1). Thermal annealing of as-deposited films at 85 °C, 120 °C and 140 °C was compared with the flash lamp annealing realised via sub-second high energy xenon light illumination from the uncoated glass side. Optimal light pulse length and energy density were found to be 2.7 ms and 8 J/cm2, respectively. According to our simulations based on the finite element model the perovskite layers underwent to a short-term heating to 350–425 °C followed by cooling to 100 °C within 3 ms. No decomposition of the perovskite was detected. Conversely its crystallinity according to the X-ray diffraction was prominently better as for thermally annealed films. Fourier-transform infrared spectroscopy revealed the effective elimination of the solvent from perovskite films by flash lamp annealing. High temperature was found to be crucial for the completeness of PbI2 reaction into the perovskite in stoichiometric films. High heating rate appeared to suppress the gel-like phase formation in super-stoichiometric films that helped to avoid the formation of pores. The flash lamp crystallised films revealed pore free microstructure with longitudinally extended grains regardless of the precursor ratio.

Photo-Induced Ignition of Different Gaseous Fuels Using Carbon Nanotubes Mixed with Metal Nanoparticles as Ignitor Agents

ABSTRACTThis article describes the photo-induced ignition process of multi-walled carbon nano-tubes (MWCNTs)/ferrocene mixtures by pulsed Xe lamps using programmable driving boards with adjustable parameters, such as variable flash rate and pulse’s energy/intensity. Varying the energy of incident light pulse, minimum ignition energy values were found as a function of mixture weight ratio, observing that a higher MWCNT amount with respect to metal nano-particles leads to lower ignition energy. The photo-induced ignition of CNTs mixed with nano-particles was then used in a properly realized experimental setup for triggering the combustion of CNT-enriched fuel mixtures. Different types of gaseous fuels mixed with air (CH4, liquid propane, and H2) were tested. The combustion process triggered by MWCNTs/ferrocene photo-ignition shows better performances, for all used gaseous fuels and for all tested air/fuel ratios, compared with those obtained by using a traditional spark plug. In particular, CNT-based photo-induced combustion evolves more rapidly with shorter ignition delays, higher peak pressure values, and a higher fuel burning rate as observed by reported experimental tests.

Symmetric and asymmetric optical multipeak solitons on a continuous wave background in the femtosecond regime.

We study symmetric and asymmetric optical multipeak solitons on a continuous wave background in the femtosecond regime of a single-mode fiber. Key characteristics of such multipeak solitons, such as the formation mechanism, propagation stability, and shape-changing collisions, are revealed in detail. Our results show that this multipeak (symmetric or asymmetric) mode could be regarded as a single pulse formed by a nonlinear superposition of a periodic wave and a single-peak (W-shaped or antidark) soliton. In particular, a phase diagram for different types of nonlinear excitations on a continuous wave background, including the unusual multipeak soliton, the W-shaped soliton, the antidark soliton, the periodic wave, and the known breather rogue wave, is established based on the explicit link between exact solution and modulation instability analysis. Numerical simulations are performed to confirm the propagation stability of the multipeak solitons with symmetric and asymmetric structures. Further, we unveil a remarkable shape-changing feature of asymmetric multipeak solitons. It is interesting that these shape-changing interactions occur not only in the intraspecific collision (soliton mutual collision) but also in the interspecific interaction (soliton-breather interaction). Our results demonstrate that each multipeak soliton exhibits the coexistence of shape change and conservation of the localized energy of a light pulse against the continuous wave background.

Avalanche mode of high-voltage overloaded p+–i–n+ diode switching to the conductive state by pulsed illumination

A simple analytical theory of high-voltage overvolting p+-i-n+-structures picosecond switching into conducting state by pulsed lighting has been developed. Relationship between parameters of structure, light pulse, external circuit and the main characteristics of the process (pulse current amplitude, delay time and duration of switching process) have been obtained and confirmed by numerical simulation. It was shown that the energy of picosecond light pulse that is needed for effective switching can be reduced by 6-7 orders of magnitude due to the intensive avalanche multiplication of electrons and holes.

Effects of trigger light pulse on open performance of nonlinear photoconductive switch

A vertical GaAs PCSS is fabricated with a thickness of 0.6 mm and a gap of 3 mm, and the triggering experiment is carried out by semiconductor laser diode. Along with enhanced electric field, the output voltage increases linearly, the output waveform is similar to the laser waveform. When bias electric field exceeds the threshold, the output voltage increases rapidly, and the output voltage impulse is faster than the laser impulse which shows PCSS turns into nonlinear mode. Except for the bias voltage, PCSS turning into nonlinear mode is also associated with the speed and the energy of the trigger light pulse. Experiment indicates that the higher trigger energy is, the faster the rise-time is, the more likely the working mode of PCSS turns into nonlinear and the needing electric field is lower. But when bias electric field falls under the threshold (about 6 kV in this experiment), PCSS can not turn into nonlinear, even if the trigger light energy is enhanced.

Optical triggering of high-voltage (18 kV-class) 4H-SiC thyristors

Optical triggering of high-voltage (18 kV-class) 4H-SiC thyristors with a single amplification step (pilot thyristor) is reported. It is demonstrated that the switch-on processes in such high-voltage structures are quite different from the switch-on processes in 12 kV 4H-SiC thyristors. In particular, the switch-on process occurs in two stages even at maximum light pulse energy and rather high anode biases.

Experimental characterization of bi-directional terahertz emission from gold-coated nanogratings

The THz radiation emission of Au-coated nanogratings (fused silica substrate, 30 nm Au layer thickness, 500 nm grating constant) upon fs laser irradiation (785 nm, 150 fs, 1 kHz, ≤1 mJ/pulse) is observed in both directions along the laser beam axis (forward and backward) and for both, illumination of the Au/air or the Au/silica interface. THz radiation along the laser beam propagation is emitted in a narrow solid angle of about 15° fwhm independent on the laser pulse fluence, the angle of incidence and the nanograting profile. The bar width and groove depth of the nanograting as well as the angle of laser beam incidence strongly affect the THz radiation yield. The energy of single THz light pulses is measured absolutely (2 fJ in the 0.3–0.38 THz range) using a highly sensitive and fast superconducting transition edge sensor. The bi-directional emission of THz radiation is in agreement with the model assumption of surface plasmon polaritons propagating simultaneously on both Au layer interfaces (Au/air and Au/silica).

Optimal Er:YAG laser irradiation parameters for debridement of microstructured fixture surfaces of titanium dental implants

Er:YAG laser (ErL) irradiation has been reported to be effective for treating peri-implant disease. The present study seeks to evaluate morphological and elemental changes induced on microstructured surfaces of dental endosseous implants by high-pulse-repetition-rate ErL irradiation and to determine the optimal irradiation conditions for debriding contaminated microstructured surfaces. In experiment 1, dual acid-etched microstructured implants were irradiated by ErL (pulse energy, 30-50mJ/pulse; repetition rate, 30Hz) with and without water spray and for used and unused contact tips. Experiment 2 compared the ErL treatment with conventional mechanical treatments (metal/plastic curettes and ultrasonic scalers). In experiment 3, five commercially available microstructures were irradiated by ErL light (pulse energy, 30-50mJ/pulse; pulse repetition rate, 30Hz) while spraying water. In experiment 4, contaminated microstructured surfaces of three failed implants were debrided by ErL irradiation. After the experiments, all treated surfaces were assessed by stereomicroscopy, scanning electron microscopy (SEM), and/or energy-dispersive X-ray spectroscopy (EDS). The stereomicroscopy, SEM, and EDS results demonstrate that, unlike mechanical treatments, ErL irradiation at 30mJ/pulse and 30Hz with water spray induced no color or morphological changes to the microstructures except for the anodized implant surface, which was easily damaged. The optimized irradiation parameters effectively removed calcified deposits from contaminated titanium microstructures without causing substantial thermal damage. ErL irradiation at pulse energies below 30mJ/pulse (10.6J/cm(2)/pulse) and 30Hz with water spray in near-contact mode seems to cause no damage and to be effective for debriding microstructured surfaces (except for anodized microstructures).

Cranz-Schardin camera with a large working distance for the observation of small scale high-speed flows

The Cranz-Schardin camera utilizes a Q-switched Nd:YAG laser and four single CCD cameras. Light pulse energy in the range of 25 mJ and pulse duration of about 5 ns is provided by the laser. The laser light is converted to incoherent light by Rhodamine-B fluorescence dye in a cuvette. The laser beam coherence is intentionally broken in order to avoid speckle. Four light fibers collect the fluorescence light and are used for illumination. Different light fiber lengths enable a delay of illumination between consecutive images. The chosen interframe time is 25 ns, corresponding to 40 × 10(6) frames per second. Exemplarily, the camera is applied to observe the bow shock in front of a water jet, propagating in air at supersonic speed. The initial phase of the formation of a jet structure is recorded.

Experimental evaluation of photoacoustic coded excitation using unipolar golay codes

Q-switched Nd:YAG lasers are commonly used as light sources for photoacoustic imaging. However, laser diodes are attractive as an alternative to Nd:YAG lasers because they are less expensive and more compact. Although laser diodes deliver about three orders of magnitude less light pulse energy than Nd:YAG lasers (tens of microjoules compared with tens of millijoules), their pulse repetition frequency (PRF) is four to five orders of magnitude higher (up to 1 MHz compared with tens of hertz); this enables the use of averaging to improve SNR without compromising the image acquisition rate. In photoacoustic imaging, the PRF is limited by the maximum acoustic time-of-flight. This limit can be overcome by using coded excitation schemes in which the coding eliminates ambiguities between echoes induced by subsequent pulses. To evaluate the benefits of photoacoustic coded excitation (PACE), the performance of unipolar Golay codes is investigated analytically and validated experimentally. PACE imaging of a copper slab using laser diodes at a PRF of 1 MHz and a modified clinical ultrasound scanner is successfully demonstrated. Considering laser safety regulations and taking into account a comparison between a laser diode system and Nd:YAG systems with respect to SNR, we conclude that PACE is feasible for small animal imaging.

The energy storage in the formation of slow light

Slow light formation in media with (i) an electromagnetically induced transparency, (ii) a doublet structure, and (iii) a single absorption line, detuned from resonance, is considered with the help of a simple model. The model is based on the description of particles in these media by a pseudospin 1/2, which is subject to two ‘orthogonal fields’. We mainly focus on the analysis of the reversible process of the particle excitation–de-excitation resulting in the temporal storage of the light-pulse energy without the pulse corruption. The influence of irreversible relaxation processes on the slow light formation is studied.

The calculation of terahertz wave power radiated from GaAs photoconductive antenna

Based on the Larmor formula, a mathematic model is established to calculate the power of THz wave radiated form the photoconductive antenna. The power of THz waves radiated by GaAs photoconductive antenna under different experimental conditions was calculated by Monte Carlo simulations. The results show that the power of THz radiation can be improved by increasing the bias electric field or the energy of triggering light pulse, and large-aperture photoconductive antenna can emit THz wave with higher power compared with photoconductive antennas with small apertures because the former can carry more photo-generated carriers.

Femtosecond laser pulse energy tunneling in the range of forbidden frequencies of a one-dimensional photonic crystal

The results of computer simulations demonstrate the possibility of light energy transmission through band gaps of a one-dimensional photonic crystal with fluctuating lengths of individual layers. In the case of weak (±5%) fluctuations, the light pulse energy partly penetrates in depth a photonic crystal. If fluctuations of the layer length are strong (±20%), the light pulse energy can be partly transmitted through the crystal.

Optical Switch-On of Silicon Carbide Thyristor

Optical switch-on of a silicon carbide thyristor has been demonstrated for the first time. A 2.6 kV 4H-SiC thyristor can be turned on by the light pulse of an ultraviolet laser with wavelength λ=337 nm. The threshold energy of the light pulse, required to turn the thyristor on, is Jth≃0.75 µJ. At light pulse energy of J∼15 µJ the thyristor is turned on extremely fast and uniformly over its full area.

Kinetic aspects of chitosan fragmentation by femtosecond laser

Kinetics of chitosan fragmentation by ultrafast laser pulses, and the effects of reactor shape, saturation of solution with oxygen and chitosan molecular weight on fragmentation were investigated. The degree of fragmentation and molecular weight distribution of the fragments were followed by viscometry and size exclusion chromatography. Chain scission increased with light pulse energy, irradiation time in sigmoidal manner, and dose in biphasic manner. It also increased with molecular weight of chitosan, indicating that larger molecules were preferentially fragmented. The polydispersity of fragments increased with irradiation time. There was only a minor change in chain scission when chitosan solution was saturated with oxygen suggesting that secondary processes involving oxidation–reduction reactions may play only a minor role, and fragmentation proceeds mainly through multi-photon absorption.