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John L Reno - One of the best experts on this subject based on the ideXlab platform.

  • 186 k operation of terahertz quantum cascade lasers based on a diagonal design
    Applied Physics Letters, 2009
    Co-Authors: Sushil Kumar, John L Reno
    Abstract:

    Resonant-phonon terahertz quantum-cascade lasers operating up to a heat-Sink Temperature of 186 K are demonstrated. This record Temperature performance is achieved based on a diagonal design, with the objective to increase the upper-state lifetime and therefore the gain at elevated Temperatures. The increased diagonality also lowers the operating current densities by limiting the flow of parasitic leakage current. Quantitatively, the diagonality is characterized by a radiative oscillator strength that is smaller by a factor of two from the least of any previously published designs. At the lasing frequency of 3.9 THz, 63 mW of peak optical power was measured at 5 K, and approximately 5 mW could still be detected at 180 K.

  • 1 9 thz quantum cascade lasers with one well injector
    Applied Physics Letters, 2006
    Co-Authors: Sushil Kumar, Benjamin S Williams, John L Reno
    Abstract:

    We report terahertz quantum-cascade lasers operating predominantly at 1.90THz with side modes as low as 1.86THz (λ≈161μm, ℏω≈7.7meV). This is the longest wavelength to date of any solid-state laser that operates without assistance of a magnetic field. Carriers are injected into the upper radiative state by using a single quantum-well injector, which resulted in a significant reduction of free-carrier losses. The laser operated up to a heat-Sink Temperature of 110K in pulsed mode, 95K in continuous wave (cw) mode, and the threshold current density at 5K was ∼140A∕cm2.

  • continuous wave operation of terahertz quantum cascade lasers above liquid nitrogen Temperature
    Applied Physics Letters, 2004
    Co-Authors: Sushil Kumar, Benjamin S Williams, Stephen Kohen, John L Reno
    Abstract:

    We report cw operation of a quantum-cascade laser at 3.2 THz (λ≈94 μm) up to a heat-Sink Temperature of 93 K. Resonant longitudinal-optical phonon scattering is used to depopulate the lower radiative state and a low-loss metal–metal waveguide is used to provide high modal confinement. Optical powers of ∼1.8 mW at 10 K and ∼400 μW at 78 K are observed from a single facet of a 40-μm-wide and 1.35-mm-long laser device. A threshold current density of 432 A/cm2 at 10 K and 552 A/cm2 at 78 K was obtained in cw mode. The same device lased up to 129 K in pulsed mode with a threshold current density of 419 A/cm2 at 5 K.

Sushil Kumar - One of the best experts on this subject based on the ideXlab platform.

  • 186 k operation of terahertz quantum cascade lasers based on a diagonal design
    Applied Physics Letters, 2009
    Co-Authors: Sushil Kumar, John L Reno
    Abstract:

    Resonant-phonon terahertz quantum-cascade lasers operating up to a heat-Sink Temperature of 186 K are demonstrated. This record Temperature performance is achieved based on a diagonal design, with the objective to increase the upper-state lifetime and therefore the gain at elevated Temperatures. The increased diagonality also lowers the operating current densities by limiting the flow of parasitic leakage current. Quantitatively, the diagonality is characterized by a radiative oscillator strength that is smaller by a factor of two from the least of any previously published designs. At the lasing frequency of 3.9 THz, 63 mW of peak optical power was measured at 5 K, and approximately 5 mW could still be detected at 180 K.

  • 1 9 thz quantum cascade lasers with one well injector
    Applied Physics Letters, 2006
    Co-Authors: Sushil Kumar, Benjamin S Williams, John L Reno
    Abstract:

    We report terahertz quantum-cascade lasers operating predominantly at 1.90THz with side modes as low as 1.86THz (λ≈161μm, ℏω≈7.7meV). This is the longest wavelength to date of any solid-state laser that operates without assistance of a magnetic field. Carriers are injected into the upper radiative state by using a single quantum-well injector, which resulted in a significant reduction of free-carrier losses. The laser operated up to a heat-Sink Temperature of 110K in pulsed mode, 95K in continuous wave (cw) mode, and the threshold current density at 5K was ∼140A∕cm2.

  • continuous wave operation of terahertz quantum cascade lasers above liquid nitrogen Temperature
    Applied Physics Letters, 2004
    Co-Authors: Sushil Kumar, Benjamin S Williams, Stephen Kohen, John L Reno
    Abstract:

    We report cw operation of a quantum-cascade laser at 3.2 THz (λ≈94 μm) up to a heat-Sink Temperature of 93 K. Resonant longitudinal-optical phonon scattering is used to depopulate the lower radiative state and a low-loss metal–metal waveguide is used to provide high modal confinement. Optical powers of ∼1.8 mW at 10 K and ∼400 μW at 78 K are observed from a single facet of a 40-μm-wide and 1.35-mm-long laser device. A threshold current density of 432 A/cm2 at 10 K and 552 A/cm2 at 78 K was obtained in cw mode. The same device lased up to 129 K in pulsed mode with a threshold current density of 419 A/cm2 at 5 K.

  • terahertz quantum cascade laser at λ 100 μm using metal waveguide for mode confinement
    Applied Physics Letters, 2003
    Co-Authors: Benjamin S Williams, Sushil Kumar, Hans Callebaut, Qing Hu, J L Reno
    Abstract:

    We report lasing at ∼3.0 THz (λ≈98–102 μm) in a quantum-cascade structure in which mode confinement is provided by a double-sided metal waveguide. The depopulation mechanism is based on resonant phonon scattering, as in our previous work. Lasing takes place in pulsed mode up to a heat-Sink Temperature of 77 K. The waveguide consists of metallic films placed above and below the 10-μm-thick multiple-quantum-well gain region, which gives low losses and a modal confinement factor of nearly unity. Fabrication takes place via low-Temperature metallic wafer bonding and subsequent substrate removal using selective etching. This type of waveguide is expected to be increasingly advantageous at even longer wavelengths.

H Zogg - One of the best experts on this subject based on the ideXlab platform.

  • pbse quantum well mid infrared vertical external cavity surface emitting laser on si substrates
    Journal of Applied Physics, 2011
    Co-Authors: M Fill, M Rahim, A Khiar, F Felder, H Zogg
    Abstract:

    Mid-infrared vertical external cavity surface emitting lasers based on PbSe/PbSrSe multi-quantum-well structures on Si-substrates are realized. A modular design allows growing the active region and the bottom Bragg mirror on two different Si-substrates, thus facilitating comparison between different structures. Lasing is observed from 3.3 to 5.1 μm wavelength and up to 52 °C heat Sink Temperature with 1.55 μm optical pumping. Simulations show that threshold powers are limited by Shockley-Read recombination with lifetimes as short as 0.1 ns. At higher Temperatures, an additional threshold power increase occurs probably due to limited carrier diffusion length and carrier leakage, caused by an unfavorable band alignment.

  • 4 5 μm wavelength vertical external cavity surface emitting laser operating above room Temperature
    Applied Physics Letters, 2009
    Co-Authors: M Rahim, A Khiar, F Felder, M Fill, H Zogg
    Abstract:

    A midinfrared vertical external cavity surface emitting laser with 4.5 μm emission wavelength and operating above room Temperature has been realized. The active part consists of a single 850 nm thick epitaxial PbSe gain layer. It is followed by a 2 1/2 pair Pb1−yEuyTe/BaF2 Bragg mirror. No microstructural processing is needed. Excitation is done optically with a 1.5 μm wavelength laser. The device operates up to 45 °C with 100 ns pulses and delivers 6 mW output power at 27 °C heat-Sink Temperature.

Yiping Dai - One of the best experts on this subject based on the ideXlab platform.

  • preliminary design and part load performance analysis of a recompression supercritical carbon dioxide cycle combined with a transcritical carbon dioxide cycle
    Energy Conversion and Management, 2020
    Co-Authors: Gang Fan, Kang Chen, Shaoxiong Zheng, Yiping Dai
    Abstract:

    Abstract Nuclear energy can be efficiently converted to electrical energy in the supercritical carbon dioxide (sCO2) power system. In this paper, a combined cycle comprising a topping sCO2 cycle and a bottoming transcritical CO2 cycle (tCO2) is investigated. Multi-objective optimization by means of a genetic algorithm is carried out to obtain better thermodynamic and economic performance in the design stage. The methodology for part-load operation of the combined sCO2-tCO2 cycle is proposed and the quantitative performance analysis is conducted for the utilization of nuclear energy. The results indicate that there exists optimal values for the maximum system exergetic efficiency and the minimum total product unit cost. A composite control strategy by adjusting the rotational speed of compressors and the opening of bypass valve is proposed for the topping sCO2 cycle operation from the point of view of both efficiency and operation range. The bottoming tCO2 cycle is well adapt to the changes of parameters in the topping sCO2 cycle and heat Sink Temperature by using the sliding pressure control strategy. The combined sCO2-tCO2 cycle can operate under 10–100% normalized generator load when the variation scope of heat Sink Temperature is 5–25 ℃.The corresponding exergetic efficiency of combined sCO2-tCO2 cycle ranges from 24.5% to 65.7%.

  • study on off design performance of transcritical co2 power cycle for the utilization of geothermal energy
    Geothermics, 2018
    Co-Authors: Yi Yang, Ziyang Cheng, Yiqian Sang, Yiping Dai
    Abstract:

    Abstract Exploiting renewable energy could greatly alleviate current severe energy situation. Transcritical CO 2 (tCO 2 ) cycle system as a type of competitive and promising energy converter could utilize low Temperature geothermal energy effectively. In this paper, the methodology for the off-design operation of tCO 2 system has been proposed and the quantitative performance analysis is carried out for the utilization of geothermal energy. With the aim at obtaining better thermodynamic and economic performance, the optimal power cycle parameters can be determined by the non-dominated sorting genetic algorithm-II (NSGA-II) in the design stage. The models of exergoeconomic analysis and main system components including turbine, pump and heat exchangers are established. The sliding pressure control strategy is applied to respond to the varieties of heat source and heat Sink conditions in the off-design stage. Results show that there exists an optimal value of geothermal resource mass flow rate to maximum the thermal efficiency. The pump rotational speed increases linearly with the increasing geothermal resource Temperature and geothermal resource mass flow rate while the pump rotational speed is gradually sensitive to the increase of heat Sink Temperature. The guideline listed in the table for pump could provide effective reference for practical operation.

  • off design performance analysis of kalina cycle for low Temperature geothermal source
    Applied Thermal Engineering, 2016
    Co-Authors: Mingkun Wang, Yiping Dai
    Abstract:

    Abstract Low Temperature geothermal sources with brilliant prospects have attracted more and more people’s attention. Kalina cycle system using ammonia water as working fluid could exploit geothermal energy effectively. In this paper, the quantitative analysis of off-design performance of Kalina cycle for the low Temperature geothermal source is conducted. The off-design models including turbine, pump and heat exchangers are established preliminarily. Genetic algorithm is used to maximize the net power output and determine the thermodynamic parameters in the design phase. The sliding pressure control strategy applied widely in existing Rankine cycle power plants is adopted to response to the variations of geothermal source mass flow rate ratio (70–120%), geothermal source Temperature (116–128 °C) and heat Sink Temperature (0–35 °C). In the off-design research scopes, the guidance for pump rotational speed adjustment is listed to provide some reference for off-design operation of geothermal power plants. The required adjustment rate of pump rotational speed is more sensitive to per unit geothermal source Temperature than per unit heat Sink Temperature. Influence of the heat Sink variation is greater than that of the geothermal source variation on the ranges of net power output and thermal efficiency.

Kamel Ghali - One of the best experts on this subject based on the ideXlab platform.

  • optimized solar powered liquid desiccant system to supply building fresh water and cooling needs
    Applied Energy, 2011
    Co-Authors: N Audah, Nesreen Ghaddar, Kamel Ghali
    Abstract:

    This paper studies the feasibility of using a solar-powered liquid desiccant system to meet both building cooling and fresh water needs in Beirut humid climate using parabolic solar concentrators as a heat source for regenerating the liquid desiccant. The water condensate is captured from the air leaving the regenerator. An integrated model of solar-powered calcium chloride liquid desiccant system for air dehumidification/humidification is developed. The LDS model predicted the amount of condensate obtained from the humid air leaving the regenerator bed when directed through a coil submerged in cold sea water. An optimization problem is formulated for selection and operation of a LDS to meet fresh water requirement and air conditioning load at minimal energy cost for a typical residential space in the Lebanon coastal climate with conditioned area of 80m2 with the objective of producing 15l of fresh drinking water a day and meet air conditioning need of residence at minimum energy cost. The optimal regeneration Temperature increases with decreased heat Sink Temperature with values of 50.5°C and 52°C corresponding to Sink Temperatures of 19°C and 16°C.

  • optimized solar powered liquid desiccant system to supply building fresh water and cooling needs
    Applied Energy, 2011
    Co-Authors: N Audah, Nesreen Ghaddar, Kamel Ghali
    Abstract:

    This paper studies the feasibility of using a solar-powered liquid desiccant system to meet both building cooling and fresh water needs in Beirut humid climate using parabolic solar concentrators as a heat source for regenerating the liquid desiccant. The water condensate is captured from the air leaving the regenerator. An integrated model of solar-powered calcium chloride liquid desiccant system for air dehumidification/humidification is developed. The LDS model predicted the amount of condensate obtained from the humid air leaving the regenerator bed when directed through a coil submerged in cold sea water. An optimization problem is formulated for selection and operation of a LDS to meet fresh water requirement and air conditioning load at minimal energy cost for a typical residential space in the Lebanon coastal climate with conditioned area of 80 m 2 with the objective of producing 15 l of fresh drinking water a day and meet air conditioning need of residence at minimum energy cost. The optimal regeneration Temperature increases with decreased heat Sink Temperature with values of 50.5 C and 52 C corresponding to Sink Temperatures of 19 C and 16 C. 2011 Published by Elsevier Ltd.