Increase In Internal Loss Research Articles

Experimental Study of the Influence of the Geometrical Parameters of the Radial Labyrinth Pump on the Pump’s Operating Parameters and Performance

Centrifugal pumps are the most common machines responsible for the increase in hydraulic energy in a piping system. Their proper design, operation, and maintenance have a strong influence on the performance of technological processes carried out in many industrial units. For the ultra-low specific speed (nq < 10) application, there is no economical reason for these pumps to be used. This is caused by an increase in internal losses in the pump. The article concerns the problem of the hydraulic operation of a new type of labyrinth pump—the radial labyrinth pump (RLP), which is a developed axial unit. The main research method involves the experimental research of hydraulic sets consisting of passive and active discs. The analyses were preceded by dimensional analysis and experimental planning. The study investigates the influence of a chosen structural parameter of both discs on the process of energy conversion obtained in the pump. The influence of parameters such as number, depth and width of the grooves, as well as inlet angle and diameter on the properties of the pump was studied and discussed in detail. The essential novelty of the article is the recognition of the hydraulic performance of the RLP with grooved discs. To extend the scope of the conducted research for the chosen hydraulic sets, a comparison of the mutual cooperation of an active disc with a smooth and grooved passive one was conducted. It was identified that not every geometric relationship of the parameters of the active and passive discs results in an increase in head with respect to cooperation with a smooth passive disc (motionless). The highest head and high efficiencies were obtained for sets with short channels with large inlet diameters—zk12 and zk13—ratios for zk12 d1ap/d2ap = 0.78, and for zk13 zk12 d1ap/d2ap = 0.81. Based on the obtained results, preliminary recommendations for the construction were made.

Спектральные характеристики полукольцевых квантово-каскадных лазеров

A half-ring resonator design of a 7-8 μm range quantum-cascade laser with different radius values has been proposed and implemented. For a quantum-cascade laser with a radius of a half-ring resonator of 191 μm, lasing with a radiation spectrum width of 474 nm (82 cm^-1) was demonstrated at low temperatures. The FSR in such lasers was determined by the whispering gallery modes typical for ring resonators. At room temperature, the width of the lasing spectrum was 190 nm (31 cm^–1), which is caused by a decrease in gain and a possible increase in internal losses with increasing temperature. An increase in the cavity radius up to 291 μm made it possible to realize room temperature lasing with whispering gallery modes with a radiation spectrum width of 249 nm (40 cm^-1), by reducing losses on the mirrors.

Optimization of the Number of Quantum Well Pairs for High-Brightness AlGaInP-Based Light Emitting Diodes

We investigated high-brightness light emitting diodes (LEDs) appropriate for general lighting applications in terms of their temperature dependent photoluminescence characteristics and device performance according to the change of quantum well pairs (QWs). As the number of QWs was increased from 2 to 35 pairs, radiative recombination efficiency and device performances significantly improved, due to the suppression of carrier overflow by decreasing the carrier density in the active region and shortening the carrier transfer time from barrier to well. At a further increase in the number of QWs to 50 pairs, however, the optical and device performances started to degrade because of the increase in internal loss in the active region, such as the well volume itself acting as light absorbing layer and due to the aluminum oxide complexes in the barrier.

InAs/InGaAs/GaAs quantum dot lasers of 1.3μm range with enhanced optical gain

Near-1.3-μm lasers based on multiple layers (2, 5 and 10) of InAs/InGaAs/GaAs quantum dots with high performance have been grown by molecular beam epitaxy. A record differential efficiency as high as 88% was achieved in laser based on 10 QD layers. Threshold current density of 100–150 A/cm 2 and differential efficiency of 75–80% were achieved simultaneously in the same device. Characteristic temperature of 150 K in 20–50°C temperature range was demonstrated for the laser based on 5 QD layers. A steep increase in internal loss with decreasing cavity length was found to limit the highest mirror loss possible for ground state lasing.

Effects of internal loss on power efficiency of mid-infrared InAs-GaInSb-AlSb quantum-well lasers and comparison with InAsSb lasers

Experimental studies of the lasing efficiency of optically pumped 4-/spl mu/m GaInSb-InAs-AlSb multiple-quantum-well (MQW) lasers that emitted >1-W peak power/facet at 80 K indicated that internal loss is the main factor that limits the power output. The internal loss coefficient and internal quantum efficiency were determined by measuring the lasing efficiency versus temperature for devices of different facet reflectivities and lengths. The internal loss coefficient was found to increase from /spl sim/18 cm/sup -1/ near 70 K to /spl sim/60-100 cm/sup -1/ near 180 K, while the internal quantum efficiency remained constant at /spl sim/47% (or /spl sim/67% with the correction for the finite absorption of the active region) from 70 to 130 K. The increase of internal loss and the decrease of external quantum efficiency versus temperature were found very similar to those of double-heterostructure InAsSb-GaSb lasers and were similarly interpreted in terms of intervalence band carrier absorption. Extrapolation of power performance for improved devices with lower internal loss indicated that high-efficiency multi-watt quasi-CW output with a broad-area brightness of /spl sim/1 MW/cm/sup 2/.sterad is possible.

Dominant mechanism for limiting the maximum operating temperature of InP-based multiple-quantum-well lasers

We study the basic mechanism for limiting the maximum operating temperature (Tm) of InP-based multiple-quantum-well (MQW) lasers emitting at a wavelength of 1.3 μm. It is shown that laser operation is characterized in terms of the temperature dependence of threshold gain (gth) by introducing a critical temperature (Tc): gth exhibits a linear relationship with temperature below Tc, while it superlinearly increases with increasing temperature above Tc. This rapid increase in gth leads to a marked increase in threshold current and a significant reduction in differential quantum efficiency above Tc. We indicate that Tc exhibits a direct correlation with Tm: the higher Tc, the higher Tm. In the temperature range above Tc, laser operation moves into a loss-multiplication regime, where a considerable portion of the injected carriers brings about a significant increase in internal loss rather than gain due to their pileup in the separate confinement heterostructure layers. We demonstrate that an anomalous increase in internal loss, which occurs at the final stage in this loss-multiplication regime, determines Tm of 1.3 μm InP-based MQW lasers.