Simultaneous effect of medicinal plants as natural photosensitizers and low-level laser on photodynamic inactivation.

Photodynamic inactivation (PDI) technology is a promising alternative to antibiotics. This technology is defined as the inhibition of bacterial growth with photosensitizers while irradiated with low-level laser light in the wavelength of 532 ± 2.08 nm. A challenging area in this field is selecting photosensitizers with antibacterial potential. In this paper, to enhance the antibacterial efficiency, the photosensitizers (the selected plant extracts) with a high absorption peak at the selected laser frequency, 532 nm, were prepared. Low-concentration ethanolic plant extracts of Hibiscus sabdariffa and Opuntia ficus-indica were found to exhibit significant antibacterial activity against, Acinetobacter baumannii ATCC 19606 and, Staphylococcus aureus ATCC 33591 as two important human pathogenic bacteria. The effectiveness of these natural photosensitizers was measured by determining their Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values and by performing a time-killing assay in the absence and the presence of laser irradiation. Our results showed that the combination of low-level laser irradiation and the selected photosensitizers had excellent potential for treating in vitro bacterial infections. Therefore, PDI technology has great potential as a viable alternative to traditional antibiotics for combating bacterial infections. This study presents a promising avenue for further exploration of PDI and the use of laser technology in medical science.

An especial configuration for an Nd:YAG end-pumped zigzag slab gain module based on crystalline polytetrafluoroethylene and a specific optical system for pump-beam delivery.

This work experimentally introduces a new single-crystal Nd:YAG end-pumped zigzag slab (EPZS) gain module based on a thin polytetrafluoroethylene (PTFE) sheet as a total internal reflection (TIR) protection layer. In this gain module, a specific optical pump-beam delivery (OPBD) system is used to improve the output beam quality (BQ) of the slab amplifier from 9.4 in a typical OPBD system to 4.7 with the total pump power of 2400 W. The average logarithmic small-signal gain (g0l) in the 0.06% Nd:YAG EPZS gain module at the laser beam incident angle of 7.1° was obtained around 0.64 for the two OPBD systems mentioned above.

The effect of population inversion saturation on the transverse mode instability threshold in high power fiber laser oscillators.

To achieve a 3.02 kW Yb-doped fiber laser oscillator, the behavior of transverse mode instability (TMI) is experimentally studied in different pumping configurations; co, hybrid, counter, and bidirectional. A comparative analysis showed that population inversion saturation has a substantial impact on TMI threshold enhancement in high power fiber oscillators. Monitoring the dynamic power exchange of fundamental mode and higher-order mode of laser output beam indicates that in a hybrid pumping scheme, simultaneous pumping with two different wavelengths enhances the TMI threshold to a great stand. Moreover, injecting a few watts of pumping light in the counter direction mitigates the TMI caused by pumping in the co-direction. Calculation of population inversion in different pumping configurations using simulation shows that higher population inversion saturation leads to increasing the TMI threshold.