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The optimized structure for the InGaAsP/GaAs quaternary material lasers (λ=0.808 μm) is investigated for the most efficient high-power operation through an experiment and theoretical study. A comparative study is performed of threshold current density Jth and differential efficiency ηd dependence on cavity length (L) for two different laser structures with different active layer thickness (150 and 300 Å) as well as for laser structures with different multiple quantum well structures. A theoretical model with a more accurate formulation for minority leakage phenomenon provides explanation for the experimental results and sets general optimization rules for other lasers with similar restrictions on the band gap and refractive index difference between the active layer and the cladding layers.

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Introduction: SARS CoV2 vaccination is effective in preventing severe COVID 19, but efficacy in reducing viral load and transmission wanes over time. In addition, the emergence of novel SARS CoV2 variants increases the threat of uncontrolled dissemination and additional antiviral therapies are urgently needed for effective containment. In previous in vitro studies Echinacea purpurea demonstrated strong antiviral activity against enveloped viruses, including SARS CoV2. In this study, we examined the potential of Echinacea purpurea in preventing and treating respiratory tract infections (RTIs) and in particular, SARS CoV2 infections. Methods: 120 healthy volunteers (m,f, 18 to 75 years) were randomly assigned to Echinacea prevention or control group without any intervention. After a run-in week, participants went through 3 prevention cycles of 2, 2 and 1 months with daily 2400mg Echinacea purpurea extract (Echinaforce, EF). The prevention cycles were interrupted by breaks of 1 week. Acute respiratory symptoms were treated with 4000 mg EF for up to 10 days, and their severity assessed via a diary. Naso/oropharyngeal swabs and venous blood samples were routinely collected every month and during acute illnesses for detection and identification of respiratory viruses, including SARS CoV2 via RT qPCR and serology. Results: Summarized over all phases of prevention, 21 and 29 samples tested positive for any virus in the EF and control group, of which 5 and 14 samples tested SARS-CoV-2 positive (RR=0.37, Chi square test, p=0.03). Overall, 10 and 14 symptomatic episodes occurred, of which 5 and 8 were COVID 19 (RR=0.70, Chi-square test, p>0.05). EF treatment when applied during acute episodes significantly reduced the overall virus load by at least 2.12 log10 or approx. 99% (t test, p<0.05), the time to virus clearance by 8.0 days for all viruses (Wilcoxon test, p=0.02) and by 4.8 days for SARS CoV2 (p>0.05) in comparison to control. Finally, EF treatment significantly reduced fever days (1 day vs 11 days, Chi square test, p=0.003) but not the overall symptom severity. There were fewer COVID-19 related hospitalizations in the EF treatment group (N=0 vs N=2). Discussion/Conclusion: EF exhibited antiviral effects and reduced the risk of viral RTIs, including SARS CoV2. By substantially reducing virus loads in infected subjects, EF offers a supportive addition to existing mandated treatments like vaccinations. Future confirmatory studies are warranted. Keywords: Echinacea purpurea, ethanolic extract, COVID 19, SARS CoV2, antiviral, prevention, randomized clinical trial Clinical Trials registration Nr: NCT05002179