•The sources of errors in thermal resistance measurements are discussed.•Spontaneous spectra allow measuring the active region temperature accurately.•Reducing of thermal resistance owning to the ...laser design optimization was measured.•Coupled-waveguides-based laser design reduceinternal loss and thermal resistance.
Thermal resistance of diode lasers with different waveguide designs has been investigated. Coupled large optical cavity (CLOC) design allows reducing internal loss and heterostructure thermal resistance of high-power InGaAs/GaAs/AlGaAs laser diodes due to the thinned p-claddings and the active region located close to the wafer p-side. Using a simple model we have calculated the thermal resistance of the heterostructure of broad-area lasers and compared the CLOC design with the reference one as well as with some of the best designs of present-day high-power lasers. The improved measurement technique has enabled us to measure reducing of thermal resistance associated with optimization of the laser wafer design. The experimental data are in good agreement with the calculations. A combination of the broadened waveguide, low internal loss and thermal resistance has resulted in good high-power performance of CLOC lasers.
We present an approach for the treatment of coupled-ridge lasers using focused ion beam (FIB) etching. We show experimentally that the FIB etching allows post-processing lateral mode tuning without ...deterioration of the main laser parameters.
Quantum well InGaAs/GaAs lasers based on narrow asymmetric waveguide were created and investigated in pulse and CW modes. Broad-area 50μm stripe lasers showed internal quantum efficiency as high as ...95%, threshold current density as low as 160 A/cm2. Wall-plug efficiency in CW mode reached the value of 75%. The obtained parameters make the concept of narrow asymmetric waveguide promising for high-power laser diodes.
—Studies of the changes in the number of γH2AX foci (a DNA double-strand break protein-marker), and Rad51 foci (a key homologous recombination protein) were conducted on human fibroblast cultures ...during the 24 hours after exposure to low (80 mGy) and intermediate (250 and 1000 mGy) doses of X-ray irradiation. Based this data, exponential curves that approximated the experimental values were constructed, and the characteristic lifetimes of the γH2AX and Rad51 foci were evaluated using the method of least squares. The ratio of the areas under the curves of changes in the number of Rad51 and γH2AX foci, calculated by the trapezium method, divided by the ratio of the characteristic lifetimes of the Rad51 and H2AX foci was used to evaluate the contribution of homologous recombination in DNA double-strand break repair. It was shown that the contribution of homologous recombination in DNA double-strand break repair during the 24 hours after exposure to 80, 250 and 1000 mGy was approximately 16, 12 and 9% respectively. Thus, the relative contribution of homologous recombination in the DNA double-strand break repair after exposure to a low dose of X-ray irradiation was approximately 1.5 times higher than that after exposure to intermediate doses. Our results suggest that DNA double-strand break repair induced after exposure to 80 mGy of X-ray irradiation is more accurate than after exposure to 250 and 1000 mGy.
An exact solution of the problem of hydraulic fracturing in a permeable medium with continuous fluid injection in a partially penetrated formation is constructed using the Perkins-Kern fracture ...model. The amount of fluid leakage from the fracture is determined using the pressure field of the fluid filtrate defined by the Shchelkachev equation (of the piezoconductivity type). Universal profiles of the fluid pressure in the fracture and the rate of fluid flow from it are obtained. It is shown that at the Perkins-Kern fracture tip, there is a dramatic increase in the leakage from the fracture.
—Intragastric administration of radioprotector indralin (B-190 drug) to outbred SPF ICR (CD-1) mice 15 minutes before X-ray irradiation at doses of 6 Gy (LD-10/30), 6.5 Gy, and 7 Gy (LD-100/30) ...increases the 30-day survival of the animals and positively affects the state of the central organs of immunity and hematopoiesis, as well as the number of peripheral blood leukocytes. In addition, a positive effect on the behavioral reactions of the irradiated animals and striated muscles strength was noted. In addition to these secondary features of the indralin positive effect, a significant reduction of radiation-induced DNA damage in spleenocytes was observed using flow cytometry analysis of phosphorylated histone Н2АХ (γН2АХ) (1 h and eight days after X-ray irradiation) and DNA-comet assay (eight days after X-ray irradiation). The abovementioned methods are recommended for experiments investigating the influence of radioprotective drugs on DNA damage induction and repair in the irradiated organism, as well as for initial searching of potential radioprotectors and assessment of their effectiveness level in clinical practice and experiments.
•Visible semiconductor lasers.•Tensile strained barriers.•High–index substrates.•Quantum dot active medium.•High resolution dark–field electron holography.
We report simulation of the conduction band ...alignment in tensile–strained GaP–enriched barrier structures and experimental results on injection lasing in the green–orange spectral range (558–605 nm) in (AlxGa1–x)0.5In0.5P–GaAs diodes containing such barriers. The wafers were grown by metal–organic vapor phase epitaxy side–by–side on (8 1 1)A, (2 1 1)A and (3 2 2)A GaAs substrates, which surface orientations were strongly tilted towards the 1 1 1A direction with respect to the (1 0 0) plane. Four sheets of GaP–rich quantum barrier insertions were applied to suppress the leakage of non–equilibrium electrons from the gain medium. Two types of the gain medium were applied. In one case 4–fold stacked tensile–strained (In,Ga)P insertions were used. Experimental data shows that self–organized vertically–correlated quantum dots (QDs) are formed on (2 1 1)A– and (3 2 2)A–oriented substrates, while corrugated quantum wires are formed on the (8 1 1)A surface. In the other case a short–period superlattice (SPSL) composed of 16–fold stacked quasi–lattice–matched 1.4 nm–thick In0.5Ga0.5P layers separated by 4 nm–thick (Al0.6Ga0.4)0.5In0.5P layers was applied. Laser diodes with 4–fold stacked QDs having a threshold current densities of ∼7–10 kA/cm2 at room temperature were realized for both (2 1 1)A and (3 2 2)A surface orientations at cavity lengths of ∼1 mm. Emission wavelength at room temperature was ∼599–603 nm. Threshold current density for the stimulated emission was as low as ∼1 kA/cm2. For (8 1 1)A–grown structures no room temperature lasing was observed. SPSL structures demonstrated lasing only at low temperatures <200 K. The shortest wavelength (558 nm, 90 K) in combination with the highest operation temperature (150 K) was realized for (3 2 2)A–oriented substrates in agreement with theoretical predictions.
We have investigated an edge-emitting tilted wave laser (TWL) with the active region based on GaInAs/GaAs quantum wells. In the TWL the wavelength stabilization is based on the coupling of the laser ...active waveguide cavity to a specially introduced thick epitaxial layer and the emission wavelength is defined by the combined cavity mode preferably by a single dominating mode. The TWL wafer has been grown by metal-organic chemical vapour deposition. Laser parameters have been investigated both in pulsed and CW mode in the temperature range of 15--60 degree C. In the temperature window of 20--50 degree C under CW excitation the lasers have shown high wavelength temperature stability with the temperature shift of 0.05 nm K-1 and threshold current stability with the characteristic temperature of 500 K. The data obtained prove the concept of thermal stability in tilted wave lasers.
PDF
