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The trade-off between microwave frequency and output power in VCSI 4H-silicon carbide (SiC) photoconductive semiconductor switch (PCSSs), based on carrier lifetime is investigated. PCSSs with two different vanadium doping concentrations are fabricated and tested across a frequency range of 0.5–2 GHz. The output power and modulation depth ratio trends with microwave frequency indicate a trade-off between microwave frequency and output power. The two devices exhibit output powers of approximately 40 W (@0.5 GHz) and 160 W (@0.5 GHz), respectively. Employing transient absorption (TA) techniques, the carrier lifetime of the two devices is determined to be 30 and 460 ps, revealing a relationship between longer carrier lifetime and increased output power. Nevertheless, the longer carrier lifetime also leads to a lower modulation depth ratio. Furthermore, when carrier lifetime ceases to be the primary constraining factor for the device’s frequency response, the upper cut-off frequency is constrained by the interstage capacitance.

A dual-stacked vertical SiC photoconductive switch is proposed for wider bandwidth in frequency-agile photonic microwave application. In order to operate in higher working-voltage and smaller interstage capacitance for wider bandwidth response, the dual stacked switch is constructed with two coaxial single device in series. The single device is fabricated on 0.5 mm-thick commercial 4H-SiC substrate using double-sided transparent electrode. The dual stacked switch can be triggered almost simultaneously by coaxial light illumination. By simulation and test, the dual-stacked switch shows a wider modulation bandwidth from 0.5 GHz to 1.8 GHz, while the single device can only operate with a upper limit frequency up to 1 GHz. In high voltage tests, the dual-stacked switch has a device power capacity of 2.56 MW, which can hold off voltage of 20 kV and output peak current of 128 A @ $50~\Omega $ load. The peak microwave-power is 102 kW @ 1.3 GHz.

Transient performance of vanadium-compensated semi-insulating 4H-silicon carbide (SiC) photoconductive semiconductor switches (PCSSs) is investigated through experimental testing and simulation under 532-nm laser triggering. Two types of impurity compensation (vanadium/nitrogen/boron) are presented: shallow-donor deep-acceptor (SDDA) and deep-donor shallow-acceptor (DDSA). The internal physical mechanism model is built to simulate the observed difference in device performance. Three vertical PCSS devices with varying doping concentrations are fabricated and tested under light peak power of several hundreds of kilowatts and operational voltages ranging from 0.5 to 10 kV. The maximum electrical peak power achieved by the SDDA device (a peak current of ~40 A) is higher than that of DDSA devices (a peak current of ~15 A). DDSA devices experienced bulk breakdown at 5 and 4 kV. The SDDA device exhibits superior photoelectric efficiency compared to DDSA devices due to the higher electron mobility. Moreover, the long tail in the photocurrent response of DDSA device is attributed to the presence of B hole traps (HTs), which leads to bulk breakdown and weak frequency response characteristics.

An axial-triggering vertical SiC photoconductive switch with Al-doped ZnO placed under the Ag electrode is developed to enhance breakdown strength and photoconductivity. Traditional and new devices with the AZO/SiC/Ag and AZO/SiC/AZO/Ag structures, respectively, were prepared. Test results show that the conductivity of the new device is approximately 1.2 times higher than that of the old one, attributable to the diffuse reflection effects of the AZO/Ag mirror. Under high bias voltages of up to 16.5 kV/mm and a 30-ns pulse width laser input, the new device shows significantly enhanced breakdown strength. The new device has a lifetime of >1E4 shots, whereas the old device has a maximum lifetime of approximately 1E2 shots. The new device can continuously output electrical pulses for 10 minutes at a 100 Hz repetition rate, 30-ns pulse width, and 100 A peak current without breakdown.

A novel low-loss selenium-based chalcohalide fiber, with a low zero-dispersion wavelength, was prepared by an innovative preparation process. The composition optimized fiber has a wide transmission range of up to 11.5 μm, a lowest fundamental mode zero-dispersion wavelength of 4.03 μm, and a minimum optical loss of 1.12 dB/m at 6.4 μm, which provides a possibility to replace As_2S_3 and As_2Se_3 in a cascade of ZrF_4−BaF_2−LaF_3−AlF_3−NaF(ZBLAN)−As_2S_3−As_2Se_3 fiber in the practical all-fiberized supercontinuum (SC) source. Meanwhile, the broadest SC spectrum, ∼1.2 to 15.2 μm, was achieved by pumping a 12-cm-long fiber with a femtosecond laser at a deep anomalous-dispersion region. Furthermore, simulations are adopted to interpret the results as well as to demonstrate spectral evolution along the fiber. To the best of our knowledge, this is the broadest SC spectrum reported in any selenium-based chalcogenide fiber.

Objective:To verify the feasibility of treating pressure ulcers (PUs) with autologous platelet-rich fibrin-based (PRF) bioactive membrane, both in vitroand in vivo.Method:An animal model using adult male Sprague-Dawley rats was used. Pressure was periodically exerted on the skin to induce localised ischaemia by using an external magnet and transplanted metal disc. After a PU developed, the rats were divided into two groups: a treatment group and a control group. Rats in the treatment group were then treated with PRF bioactive membrane every three days.Results:A total of 20 rats were used in this study. At days three and seven, the PU area in the PRF bioactive membrane-treated group was significantly smaller than that in the control group, and after 14 days of treatment, the PUs in the PRF bioactive membrane treatment group had healed. Haemotoxylin and eosin staining, immunohistochemistry and Western blot results indicated that PRF bioactive membrane induced wound healing by increasing the thickness of the regenerated epidermis and by upregulating vascular endothelial growth factor expression. Further, we found that different concentrations of rat autologous PRF soluble factors extraction components could significantly promote rat aortic endothelial cell proliferation, wound healing and migration ability in vitro.Conclusion:Overall, results indicate that PRF bioactive membrane promotes PU healing in rats. Thus, it may represent a natural and effective wound-healing tool for use in the treatment of clinical skin PUs in humans in the future.

In this Letter, a high-power supercontinuum (SC) laser source which spanned from 1.9 to 3.6 μm with an all-fiber configuration was reported. This SC laser was obtained by concatenating a thulium-doped fiber amplifier (TDFA) and a 12 cm long highly nonlinear germania fiber. A 1.9–2.7 μm SC laser from the TDFA was spectrally broadened continuously into the mid-infrared region (>3  μm) in the following germania fiber. When the repetition rate was 2 MHz, the obtained SC laser had a maximum output power of 6.12 W with an optical conversion efficiency of 15.3% with respect to the TDFA pump power. The SC laser had a spectral bandwidth of 1506 nm ranging from 1944 to 3450 nm at the −20  dB level. The SC power with wavelengths >3  μm was 2.9 W, corresponding to a high power ratio of 47.4% in the mid-infrared region. The achieved power ratio in the mid-infrared region, as well as the long wavelength cutoff, to the best of our knowledge, were the best results ever reported in germania fibers.

An ultra-flat high-power short-wave infrared super-continuum (SC) source generated in an all-fiber thulium-doped fiber amplifier (TDFA) is reported. The SC had a high-spectral flatness with a 10 dB spectral bandwidth spanning from 1970 to 2431 nm and a power spectral density >23  dBm/nm. The output SC beam had Gaussian-shape profiles with a maximum average power of 101.6 W, a SC pulse repetition rate of 2 MHz, and a temporal duration of ∼5  ns. Benefiting from the high duty cycle of the 2 μm seed pulses, the power conversion efficiency from the 793 nm pump light to the maximal SC output power in the TDFA was as high as 35.4%, and the slope efficiency of the TDFA was linearly fitted to be 36.5%. Long-term high-power operation of the SC source showed its outstanding temporal stability. To the best of the authors’ knowledge, the results obtained in this Letter represent a new power record for ultra-flat SC in the short-wave infrared region.

To determine the effects of various pre-analytical variables on the values of activated partial thromboplastin time (APTT), D-dimers, fibrinogen (Fbg), prothrombin time (PT) and thrombin time (TT). Samples from 120 hepatitis B patients were divided into three groups based on storage time (0–24h), mechanical agitation and separation into plasma. In all groups, samples were stored at room temperature and 4°C. The percentage changes compared to the baseline were calculated. Clinically relevant differences were defined as a more than 10 change. If less than 25 samples showed relevant differences, the effect of the pre-analytical variable was considered moderate; if more than 25 of samples showed relevant differences, the effect was deemed large. Clinically relevant differences in APTT were found in separated samples stored for 24h. No relevant differences were seen in the other test results. All tested pre-analytical variables had a moderate effect on the D-dimer, Fbg, PT and TT values. Storage for 24h had a large effect on APTT. Coagulation test results were unaffected by temperature, storage time, mechanical agitation and sample separation. Specimens for D-dimer, Fbg, PT and TT tests could be stored for 24h, and specimens for APTT could be stored for 8h.

AbstractNarrowband microwave generation with tuneable frequency is demonstrated by illuminating a photoconductive semiconductor switch (PCSS) with a burst-mode fibre laser. The whole system is composed of a high-power linearly polarized burst-mode pulsed fibre laser and a linear-state PCSS. To obtain a high-performance microwave signal, a desired envelope of burst is necessary and a pulse pre-compensation technique is adopted to avoid envelope distortion induced by the gain-saturation effect. Resulting from the technique, homogenous peak power distribution in each burst is ensured. The maximum energy of the laser burst pulse reaches 200 μJ with a burst duration of 100 ns at the average power of 10 W, corresponding to a peak power of 4 kW. When the PCSS is illuminated by the burst-mode fibre laser, narrowband microwave generation with tuneable frequency (0.80–1.12 GHz) is obtained with a power up to 300 W. To the best of the authors’ knowledge, it is the first demonstration of frequency-tuneable narrowband microwave generation based on a fibre laser. The high-power burst-mode fibre laser reported here has great potential for generating high-power arbitrary microwave signals for a great deal of applicable demands such as smart adaptive radar and intelligent high-power microwave systems.