- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Cooling atomic ions with visible and infra-red light
摘要： We demonstrate the ability to load, cool and detect singly charged calcium ions in a surface electrode trap using only visible and infrared lasers for the trapped-ion control. As opposed to the standard methods of cooling using dipole-allowed transitions, we combine power broadening of a quadrupole transition at 729 nm with quenching of the upper level using a dipole allowed transition at 854 nm. By observing the resulting 393 nm ?uorescence we are able to perform background-free detection of the ion. We show that this system can be used to smoothly transition between the Doppler cooling and sideband cooling regimes, and verify theoretical predictions throughout this range. We achieve scattering rates which reliably allow recooling after collision events and allow ions to be loaded from a thermal atomic beam. This work is compatible with recent advances in optical waveguides, and thus opens a path in current technologies for large-scale quantum information processing. In situations where dielectric materials are placed close to trapped ions, it carries the additional advantage of using wavelengths which do not lead to signi?cant charging, which should facilitate high rate optical interfaces between remotely held ions.
关键词： trapped ions,laser cooling,quantum optics
更新于2025-09-23 15:21:21
-
3D Magneto-Optical Trap of Yttrium Monoxide
摘要： We report three-dimensional trapping of an oxide molecule (YO), using a radio-frequency magneto-optical trap (MOT). The total number of molecules trapped is ～1.5 × 104, with a temperature of 4.1(5) mK. This diversifies the frontier of molecules that are laser coolable and paves the way for the second-stage narrow-line cooling in this molecule to the microkelvin regime. Futhermore, the new challenges of creating a 3D MOT of YO resolved here indicate that MOTs of more complex nonlinear molecules should be feasible as well.
关键词： laser cooling,molecular trapping,yttrium monoxide,3D magneto-optical trap
更新于2025-09-23 15:21:21
-
[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Improved Multiscale Model of Heat Exchange at the Apex of Carbon Nanotube Fiber Cathodes
摘要： A multiscale model of field emission (FE) from carbon nanotube fibers (CNFs) is developed which includes a detailed treatment of the heat exchange mechanisms in the array of carbon nanotubes (CNTs) located at the tip of the fiber. The model takes into account Joule heating within the fiber, radiative cooling at the fiber apex, and the transition from Nottingham heating to Henderson cooling in the CNTs in the array at the apex of the fiber as the external electric field is increased. The model uses numerical calculations of the current emitted from each CNT and the energy exchange at their tips. The model predicts the fraction of CNTs being destroyed as a function of the applied external electric field. For the surviving CNTs, the model also predicts the fraction of CNTs either undergoing Henderson cooling or Nottingham heating for both the up and down sweeps of the applied external electrical field. This investigation sheds new light on the FE properties on CNFs.
关键词： carbon nanotube fibers,Multiscale Model,field emission,Henderson cooling,self-heating effects,Nottingham heating
更新于2025-09-23 15:21:21
-
First demonstration of a cryocooler conduction cooled superconducting radiofrequency cavity operating at practical cw accelerating gradients
摘要： We demonstrate practical accelerating gradients on a superconducting radiofrequency (SRF) accelerator cavity with cryocooler conduction cooling, a cooling technique that does not involve the complexities of the conventional liquid helium bath. A design is first presented that enables conduction cooling an elliptical-cell SRF cavity. Implementing this design, a single cell 650 MHz Nb3Sn cavity coupled using high purity aluminum thermal links to a 4 K pulse tube cryocooler generated accelerating gradients up to 6.6 MV/m at 100% duty cycle. The experiments were carried out with the cavity-cryocooler assembly in a simple vacuum vessel, completely free of circulating liquid cryogens. We anticipate that this cryocooling technique will make the SRF technology accessible to interested accelerator researchers who lack access to full-stack helium cryogenic systems. Furthermore, the technique can lead to SRF based compact sources of high average power electron beams for environmental protection and industrial applications. A concept of such an SRF compact accelerator is presented.
关键词： superconducting radiofrequency (SRF) cavity,cryocooler conduction cooling,electron beams,accelerating gradients,Nb3Sn
更新于2025-09-23 15:21:01
-
Performance evaluation and optimization of the cooling system of a hybrid thermionic-photovoltaic converter
摘要： Hybrid thermionic-photovoltaic (TIPV) converters are efficient and clean solutions for the direct conversion of thermal energy to electricity, taking advantage of both the photovoltaic and thermionic phenomena. An important hurdle for their efficient operation is the overheating of the PV cell integrated within the TIPV anode, due to partial conversion of the emitted electron and photon fluxes to thermal heat. This obstacle needs to be overcome with an efficient, yet practical, cooler. In this work, a copper plate heat spreader is experimentally tested for TIPV cathode temperatures up to 1450 °C, whilst its performance is also assessed using a validated CFD model for temperatures up to ~2000 °C. A multi-parametric analysis is conducted testing two coolants: i) a water/ethylene glycol mixture at various temperatures (?5–40 °C) and mass flow rates (0.05–0.4 kg·s?1), and, ii) cryogenic liquid nitrogen at a temperature of ?196 °C and mass flow rate of 0.074 kg·s?1. Numerical results reveal that with water/ethylene mixture the PV can withstand heat fluxes up to 360 W·cm?2, without its temperature exceeding 100 °C. For higher thermal fluxes (360–600 W·cm?2), cryogenic liquid nitrogen is found to prevent the PV overheating and, therefore, is an attractive coolant; however, it poses safety concerns due to its possible boiling. Finally, two additional cooling system designs are proposed, a heat sink with straight fins and another with copper pipes, which offer higher heat transfer areas, but are more difficult to manufacture, than the copper plate heat spreader.
关键词： Ultra-high power density,Copper plate heat spreader,Cooling system design optimization,Electronic device,Computational fluid dynamics (CFD)
更新于2025-09-23 15:21:01
-
[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Direct Fluid Cooling of Concentrator Photovoltaics for Hybrid Photovoltaic-Solar Thermal Energy Conversion
摘要： A spectrum-splitting photovoltaic module is developed for hybrid photovoltaic-solar thermal energy conversion using direct fluid cooling (DFC) of partially transmissive concentrator photovoltaic cells. The waste heat generated in photovoltaic cells can be more efficiently extracted by flowing a heat transfer fluid in direct contact with both sides of the cells. The module also acts as a beam splitter, dividing the incident light into two parts. Photons with higher energy than the bandgap of the cells are absorbed in cells, while photons with lower energy are passed through the infrared-transmissive module to a thermal receiver. Optical modeling (experimental) shows 63.2% (34.3%) out-of-band transmittance through the cell regions and 90.4% (89.0%) full spectrum transmittance through the surrounding bypass region. Thermal modelling verifies the direct cooling fluid method is an effective way to maintain cell temperature < 110℃. Electrical power conversion efficiency in a first prototype module is 79% of the bare cell efficiency. Fluid flow characterization shows laminar flow. The modules are currently undergoing field testing.
关键词： hybrid CPV/T system,active cooling,silicone oil heat transfer fluid,CPV
更新于2025-09-23 15:21:01
-
Ultrafast Electron Cooling and Decay in Monolayer WS <sub/>2</sub> Revealed by Time- and Energy-Resolved Photoemission Electron Microscopy
摘要： A comprehensive understanding of the ultrafast electron dynamics in two-dimensional transition metal dichalcogenides (TMDs) is necessary for their applications in optoelectronic devices. In this work, we contribute a study of ultrafast electron cooling and decay dynamics in the supported and suspended monolayer WS2 by time- and energy-resolved photoemission electron microscopy (PEEM). Electron cooling in the Q valley of the conduction band is clearly resolved in energy and time, on a timescale of 0.3 ps. Electron decay is mainly via defect trapping process on a timescale of several picoseconds. We observed that the trap states can be produced and increased by laser illumination under ultra-high vacuum, and the higher local optical-field intensity led to the faster increase of trap states. The enhanced defect trapping could significantly modify the carrier dynamics and should be paid attention to in photoemission experiments for two-dimensional materials.
关键词： transition metal dichalcogenides,defect trapping,ultrafast dynamics,energy-resolved,electron cooling,photoemission electron microscopy
更新于2025-09-23 15:21:01
-
High-resolution infrared spectroscopy of jet cooled CH <sub/>2</sub> Br radicals: The symmetric CH stretch manifold and absence of nuclear spin cooling
摘要： Direct laser absorption of a slit supersonic discharge expansion provides the first high-resolution spectroscopic results on the symmetric CH stretch excitation (ν1) of the bromomethyl (CH2Br) radical in the ground electronic state. Narrowband (<1 MHz) mid-infrared radiation is produced by difference-frequency generation of two visible laser beams, with the open shell halohydrocarbon radical generated by electron dissociative attachment of CH2Br2 in a discharge and rapidly cooled to Trot = 18 ± 1 K in the subsequent slit-jet supersonic expansion. A rovibrational structure in the radical spectrum is fully resolved, as well as additional splittings due to spin-rotation effects and 79Br/81Br isotopologues in natural abundance. Spectroscopic constants and band origins are determined by fitting the transition frequencies to a non-rigid Watson Hamiltonian, yielding results consistent with a vibrationally averaged planar radical and an unpaired electron in the out-of-plane pπ orbital. Additionally, extensive satellite band structure from a vibrational hot band is observed and analyzed. The hot band data is compared to CFOUR/VPT2 (CCSD(T)cc-pVQZ) ab initio anharmonic predictions of the vibration rotation alpha matrix, which permits unambiguous assignment to CH2 symmetric-stretch excitation built on the singly excited CH2 out-of-plane bending mode (ν1 + ν4 ← ν4). Longitudinal cooling of the Doppler width in the slit-jet expansion geometry also reveals partially resolved hyperfine structure on transitions out of the lowest angular momentum states in excellent agreement with predictions based on microwave studies. High level ab initio MOLPRO calculations [CCSD(T)-f12b/VnZ-f12 (n = 3, 4, CBS)] are also performed with explicitly correlated f12 electron methods for the out-of-plane CH2 bending mode over the halogen series CH2X (X = F, Cl, Br, I), which clearly reveals a non-planar geometry for X = F (with a ΔE ≈ 0.3 kcal/mol barrier) and yet planar equilibrium geometries for X = Cl, Br, and I. Finally, a detailed Boltzmann analysis of the transition intensities provides support for negligible collisional equilibration of the entangled H atom nuclear spin states on the few hundred microsecond time scale and high collision densities of a slit supersonic expansion.
关键词： infrared spectroscopy,jet cooled CH2Br radicals,symmetric CH stretch manifold,nuclear spin cooling
更新于2025-09-23 15:21:01
-
Investigation of photovoltaic thermoelectric air-conditioning system for room application under tropical climate
摘要： Photovoltaic thermoelectric air-conditioning system (PT A/C) system could be a greater option compared to conventional A/C system as it is Freon-free and absence of moving parts. This study investigated the cooling and dehumidification performance of a PT A/C that is solely powered by solar energy under tropical climate conditions. The system is built with 9 pieces of thermoelectric to provide cooling for a test chamber of 3.6 m3 volume. The effect of input current on the system’s cooling and moisture removal rate were investigated and results showed that 5 A is the optimum current level, providing an average of 181 W cooling capacity and 0.14 ltr/hour of moisture removal rate at the given ambient conditions. During the operation, indoor temperature of the test chamber was 4 °C lower than the unconditioned chamber and 7.7 °C compared to the ambient temperature. Whereas the indoor relative humidity varies between 58~83 %. Furthermore, for a 12 hours operation, the system consumes 1.45 kWh of energy, and delivered temperature between 23.8 to 27.8 oC at 5 A.
关键词： Air-conditioning,Cooling,Relative humidity,Thermoelectric
更新于2025-09-23 15:21:01
-
Thermal Assessment of Laminar Flow Liquid Cooling Blocks for LED Circuit Boards Used in Automotive Headlight Assemblies
摘要： This research work presents a comparative thermal performance assessment of the laminar flow cooling blocks produced for automotive headlight assembly using a high power Light Emitting Diode (LED) chip. A three-dimensional numerical model with conjugate heat transfer in solid and fluid domains was used. Laminar flow was considered in the present analysis. The validation of the numerical model was realized by using the measured data from the test rig. It was observed that substantial temperature variations were occurred around the LED chip owing to volumetric heat generation. The cooling board with lower height performs better thermal performance but higher pressure drop for the same mass flow rates. The cooling board with the finned cover plate performs better thermal performance but results in an increased pressure drop for the same mass flow rates. Increasing the power of the LED results in higher temperature values for the same mass flow rates. The junction temperature is highly dependent on the mass flow rates and LED power. It can be controlled by means of the mass flow rate of the coolant fluid. New Nusselt number correlations are proposed for laminar flow mini-channel liquid cooling block applications.
关键词： laminar flow,CFD,LED chip,finned plate,junction temperature,automotive headlight,liquid cooling
更新于2025-09-23 15:21:01