We report room temperature injection lasing in the yellow-orange spectral range (599-605 nm) in (Al
Ga
)
In
P-GaAs diodes with 4 layers of tensile-strained In
Ga
P quantum dot-like insertions. The ...wafers were grown by metal-organic vapor phase epitaxy side-by-side on (811), (211) and (322) GaAs substrates tilted towards the direction with respect to the (100) surface. Four sheets of GaP-rich quantum barrier insertions were applied to suppress leakage of non-equilibrium electrons from the gain medium. Laser diodes having a threshold current densities of ~7-10 kA/cm
at room temperature were realized for both (211) and (322) surface orientations at cavity lengths of ~1mm. Emission wavelength at room temperature ~600 nm is shorter by ~8 nm than previously reported. As an opposite example, the devices grown on (811) GaAs substrates did not show lasing at room temperature.
Bacteria, plants, and higher and lower animals have evolved an innate immune system as a first line of defense against microbial invasion. Some of these organisms produce antimicrobial peptides ...(AMPs) as a part of this chemical immune system. AMPs exert their antimicrobial activity by binding to components of the microbe's surface and disrupting the membrane. The overall goal of this study was to apply the AMP magainin I as a recognition element for Escherichia coli O157:H7 and Salmonella typhimurium detection on an array-based biosensor. We immobilized magainin I on silanized glass slides using biotin−avidin chemistry, as well as through direct covalent attachment. Cy5-labeled, heat-killed cells were used to demonstrate that the immobilized magainin I can bind Salmonella with detection limits similar to analogous antibody-based assays. Detection limits for E. coli were higher than in analogous antibody-based assays, but it is expected that other AMPs may possess higher affinities for this target. The results showed that both specific and nonspecific binding strongly depend on the method used for peptide immobilization. Direct attachment of magainin to the substrate surface not only decreased nonspecific cell binding but also resulted in improved detection limits for both Salmonella and E. coli.
Single-mode vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts, composite distributed Bragg reflectors, and a rhomboidal selectively-oxidised current aperture are studied. It ...is shown that the use of a rhomboidal current aperture allows the light output polarisation to be fixed without using a special surface relief and leads to efficient narrowing of the emission line with retaining a high slope efficiency. The developed VCSELs have a high output power (exceeding 1 mW), a threshold current below 1 mA, an effective modulation frequency exceeding 5 GHz, and a linewidth smaller than 60 MHz at increased (65 - 75 °C) temperatures and are promising for application in compact Cs vapour cell atomic clocks.
Edge-emitting lasers with active regions based on novel InGaAs/GaAs quantum heterostructures of transitional dimensionality, i.e., quantum well-dots, which are intermediate in properties between ...quantum wells and quantum dots, are studied. It is shown that the rate of the lasing-wavelength blue shift decreases with increasing number of quantum well-dot layers in the active region and with increasing optical confinement factor as the cavity length decreases. In a laser with 10 quantum well-dot layers, the lasing-wavelength position remains within the limits of the fundamental optical transition down to the smallest cavity lengths (100 μm). In devices with a single quantum well-dot layer and/or with a low optical confinement factor, lasing directly switches from the ground state to waveguide states omitting excited states below ≤200 μm. Such an effect has not been observed in quantum-well- and quantum-dot lasers and can be attributed to the abnormally low density of excited states in quantum well-dots.
The results of comparative analysis of the spectral and threshold characteristics of room-temperature injection microdisk lasers of the spectral range 1.2×× μm with different active regions, notably, ...InGaAsN/GaAs quantum wells or InAs/InGaAs/GaAs quantum dots are presented. It is found that microlasers of a comparable size with quantum wells possess a larger laser generation threshold when compared with microlasers with quantum dots. At the same time, the latter are characterized by a noticeably smaller fraction of emitted power corresponding to laser modes. The jump to lasing via an excited-state optical transition is also characteristic for them. Microdisk lasers based on InGaAsN alloy do not have these disadvantages.
We demonstrate a record low threshold current density of 250 A/cm
2
in a quantum dot microdisk laser with a 31-μm diameter operating at room temperature in continuous wave regime without temperature ...stabilization. This low threshold current density is very close to the transparency current density estimated in broad-area edge-emitting lasers made of the same epitaxial wafer.
An InAs/InGaAs quantum dot laser with a heterostructure epitaxially grown on a silicon substrate was used to fabricate injection microdisk lasers of different diameters (15-31 µm). A post-growth ...process includes photolithography and deep dry etching. No surface protection/passivation is applied. The microlasers are capable of operating heatsink-free in a continuous-wave regime at room and elevated temperatures. A record-low threshold current density of 0.36 kA/cm
was achieved in 31 µm diameter microdisks operating uncooled. In microlasers with a diameter of 15 µm, the minimum threshold current density was found to be 0.68 kA/cm
. Thermal resistance of microdisk lasers monolithically grown on silicon agrees well with that of microdisks on GaAs substrates. The ageing test performed for microdisk lasers on silicon during 1000 h at a constant current revealed that the output power dropped by only ~9%. A preliminary estimate of the lifetime for quantum-dot (QD) microlasers on silicon (defined by a double drop of the power) is 83,000 h. Quantum dot microdisk lasers made of a heterostructure grown on GaAs were transferred onto a silicon wafer using indium bonding. Microlasers have a joint electrical contact over a residual
+ GaAs substrate, whereas their individual addressing is achieved by placing them down on a
-contact to separate contact pads. These microdisks hybridly integrated to silicon laser at room temperature in a continuous-wave mode. No effect of non-native substrate on device characteristics was found.
The characteristics of a single-photon emitter based on a semiconductor quantum dot, such as their indistinguishability and brightness, depend on the stability of the recombination channel, which can ...switch spontaneously between exciton and trion. We show that dominant recombination through neutral exciton states can be achieved by careful control of the doping profile near an epitaxial InAs/GaAs quantum dot placed in a columnar microcavity with distributed Bragg reflectors. The Hong-Ou-Mandel experiments carried out in the fabricated device demonstrate the degree of indistinguishability of 91% of successively emitted single photons within 242 ns at an efficiency of 10% inside a single-mode optical fiber. The achieved brightness made it possible to implement spatio-temporal demultiplexing of photons in six independent spatial modes with an in-fiber generation frequency of more than 0.1 Hz.
•Controlling the doping profile allows to excite principally neutral exciton states.•The single-photon source demonstrates 10% end-to-end.•The implementation of photons demultiplexing in 6 spatial modes is shown.
The last interglacial (LI) and Holocene changes in annual precipitation (
P
ann), the mean temperature of the warmest (
T
w) and coldest (
T
c) month and the moisture index (
α) were reconstructed ...from continuous pollen records from Lake Baikal. The Holocene core (52°31′N, 106°09′E) presented in this study was recovered from a depth of 355 m in the 25-km wide underwater Buguldeika saddle separating the southern sub-basin of Lake Baikal from its central sub-basin. The biome reconstruction shows that tundra and steppe biomes have highest scores during ca. 15,000–13,300 cal. years B.P. and that taiga becomes a dominant vegetation type after ca. 13,300 cal. years B.P. Our quantitative reconstruction indicates an onset of relatively warm and wet conditions soon after ca. 10,000 cal. years B.P. The warmest and wettest climate with
T
w
∼
16 °C,
P
ann
∼
480 mm and
α
∼
0.9–1 has been reconstructed for ca. 9000–7000 cal. years B.P. In the Lake Baikal region this interval is characterized by the appearance and spread of hunter communities (Kitoi culture). Consistently a hiatus in the regional archaeological record (4900–4200 years B.C. or 6850–6150 cal. years B.P.) coincides with the interval of a major climate deterioration which followed the ‘climatic optimum’. An attempt to find a relationship between the archaeological record and a spread of steppe and meadow communities in the Lake Baikal region demonstrates that despite a long habitation of the area the human impact on vegetation was local rather than regional and likely did not affect the pollen record from Lake Baikal. The reconstructed peaks in the steppe biome scores during the last 9000 years are consistent with short (one to five hundred year) episodes of weak Pacific (summer) monsoon supporting our interpretation that the Holocene vegetation changes around Lake Baikal are associated with large-scale circulation processes controlling regional water balance rather than with human activities. Thus, our study proves the suitability of Lake Baikal pollen data for the reconstruction of natural vegetation and climate dynamics through the whole period from the onset of the LI to the present. Comparison of the recent and the last interglacial suggests that the Holocene ‘climatic optimum’ was less pronounced (e.g. lower summer and winter temperatures and annual precipitation sums) than that of the LI. On the other hand, pollen records demonstrate that the Holocene ‘forest phase’ already lasts some thousand years longer than that of the LI. The interglacial vegetation dynamics derived from the Lake Baikal pollen records can be satisfactorily explained by reconstructed changes in summer and winter temperatures and in available moisture. The interglacial vegetation around Lake Baikal is dominated by the boreal forests, which are associated with a generally warm and wet climate. The high sea level associated with decreased ice volume appears to have had a greater impact on the Siberian environments during the last and the recent interglacial than the direct effect of lower-than-present winter insolation. Reconstructed changes in the winter temperature correlate well with changes in the sea level and global ice volume, while the summer temperatures derived from the Lake Baikal pollen records track changes in the summer insolation.
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.
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