Nonequilibrium carrier recombination in highly excited epitaxial layers of 4H–SiC and free standing 3C–SiC was analyzed numerically and studied experimentally by the time-resolved free carrier absorption (FCA) technique. The measurement setup combined interband carrier excitation by a picosecond laser pulse and probing of carrier dynamics at excess carrier densities in the ΔN=1017–1020 cm−3 range by optically or electronically delayed probe pulses, thus providing temporal resolution of 10 ps and 10 ns, respectively. FCA decay kinetics at different excitation levels and subsequent numerical modeling were used to determine the bulk lifetime, surface recombination velocity, and bimolecular (B) and Auger recombination (C) coefficients at 300 K. Bulk lifetimes of ∼800 ns and ∼65 ns were determined in 4H and 3C epitaxial layers, respectively. The numerical fitting of FCA kinetics in the 4H layer provided values of B=(1.2±0.4)×10−12 cm3/s and C=(7±4)×10−31 cm6/s at lower excitations while the Auger coefficient decreased to C=(0.8±0.2)×10−31 cm6/s at ΔN∼1020 cm−3 due to screening of the Coulomb-enhanced Auger recombination. In 3C crystals, these values were measured to be B=(2.0±0.5)×10−12 cm3/s and C=(2.0±0.5)×10−32 cm6/s. The tendency for a strongly increased surface recombination rate in 3C at high excitation conditions was observed experimentally and associated with the screening of the surface potential by the high density carrier plasma.

We demonstrate applicability of time‐resolved free‐carrier absorption and transient grating techniques for investigation of carrier recombination and diffusion features in a bulk diamond. Carrier injection into a 1 mm thick, IIa type high‐pressure high‐temperature grown layer was realized by two‐photon absorption of ∼5 ps laser pulse at 351 nm wavelength. Kinetics of differential transmission in 80–800 K range at various excess carrier densities provided carrier lifetimes of 360 ns at room temperature and their temperature dependences. A linear increase of carrier recombination rate with injection in 450–800 K range resulted in carrier lifetimes up to 1 ns and was fitted by effective coefficient B* = 2 × 10−11– 4 × 10−9 cm3/s. The latter process was attributed to a trap‐assisted Auger recombination (TAAR) with coefficient CTAAR = B*/NTrap and tentatively ascribed to nitrogen related traps. An ambipolar carrier mobility with its peak value of ∼1500 cm2/Vs at room temperature was measured by transient grating technique at ∼1.5 × 1015 cm−3 excess carrier density.

Aims:  The aim of this study was to evaluate the inactivation efficiency of Listeria monocytogenes ATCL3C 7644 and Salmonella enterica serovar Typhimurium strain DS88 by combined treatment of hypericin (Hyp)‐based photosensitization and high power pulsed light (HPPL). Methods and Results:  Cells were incubated with Hyp (1 × 10−5 or 1 × 10−7 mol l−1) in PBS and illuminated with a light λ = 585 nm. For the combined treatment, bacteria were, after photosensitization, exposed to 350 pulses of HPPL (UV light dose = 0·023 J cm−2). Fluorescence measurements were performed to evaluate optimal time for cell–Hyp interaction. Results indicate that Hyp tends to bind both Listeria and Salmonella. After photosensitization treatment, Listeria population was reduced 7 log, whereas Salmonella was inactivated just 1 log. Electron photomicrograps of Salmonella and Listeria confirmed that photosensitization induced total collapse of the Listeria cell wall, but not that of Salmonella. After combined photosensitization–HPPL treatment, the population of Listeria was diminished by 7 log and Salmonella by 6·7 log. Conclusions:  Listeria can be effectively inactivated by Hyp‐based photosensitization (7 log), whereas Salmonella is more resistant to photosensitization and can be inactivated just by 1 log in vitro. Combined treatment of photosensitization and pulsed light inactivates effectively (6·7–7 log) both the Gram‐positive and the more resistant to photosensitization Gram‐negative bacteria. Significance and Impact of the Study:  A new approach to combat Gram‐positive and Gram‐negative bacteria is proposed, combining photosensitization with high power pulsed light.

Aims:  The aim of this study was to construct an advanced high‐power pulsed light device for decontamination of food matrix and to evaluate its antibacterial efficiency. Key parameters of constructed device‐emitted light spectrum, pulse duration, pulse power density, frequency of pulses, dependence of emitted spectrum on input voltage, irradiation homogenicity, possible thermal effects as well as antimicrobial efficiency were evaluated. Methods and Results:  Antimicrobial efficiency of high‐power pulsed light technique was demonstrated and evaluated by two independent methods – spread plate and Miles–Misra method. Viability of Salmonella typhimurium as function of a given light dose (number of pulses) and pulse frequency was examined. According to the data obtained, viability of Salmonella typhimurium reduced by 7 log order after 100 light pulses with power density 133 W cm−2. In addition, data indicate, that the pulse frequency did not influence the outcome of pathogen inactivation in the region 1–5 Hz. Moreover, no hyperthermic effect was detected during irradiation even after 500 pulses on all shelves with different distance from light source and subsequently different pulse power density (0–252 W cm−2). Conclusion:  Newly constructed high‐power pulsed light technique is effective nonthermal tool for inactivation of Salmonella typhimurium even by 7 log order in vitro. Significance and Impact of the Study:  Novel advanced high‐power pulsed light device can be a useful tool for development of nonthermal food decontamination technologies.

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.