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High-sensitive optical temperature sensing based on 5D1 emission of Eu3+ in YVO4
摘要： By studying the temperature-induced red-shift of the V-O charge transfer band (CTB) edge in YVO4:10% Eu3+, we demonstrate a high-sensitive strategy for optical temperature sensing using the combination of the temperature-induced enhancement of the excitation in the tail of the CTB and the thermal population of 5D1 state of Eu3+. Under a constant 358 nm excitation, the integrated emission intensity corresponding to 5D1 → 7F1 transition of Eu3+ exhibits drastic temperature dependence ranging from 300 to 480 K. A high relative sensitivity SR was obtained to be 3923/T2. Temperature cycling tests were performed to evaluate the reusability and feasibility as temperature sensors. Our results indicate the potential use of the proposed strategy for high performance optical thermometry.
关键词： Charge transfer band,Rare earth ions,Thermal population,Optical temperature sensing,Luminescence
更新于2025-09-19 17:15:36
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Benchmark stars for <i>Gaia</i> Fundamental properties of the Population II star HD?140283 from interferometric, spectroscopic, and photometric data
摘要： Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental properties of the stars must first be determined. HD 140283 is the closest and brightest metal-poor Population II halo star (distance = 58 pc and V = 7.21), an ideal target that allows us to approach these questions, and one of a list of 34 benchmark stars defined for Gaia astrophysical parameter calibration. In the framework of characterizing these benchmark stars, we determined the fundamental properties of HD 140283 (radius, mass, age, and effective temperature) by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer VEGA on the CHARA array and we determined a 1D limb-darkened angular diameter of θ1D = 0.353 ± 0.013 milliarcsec. Using photometry from the literature we derived the bolometric flux in two ways: a zero reddening solution (AV = 0.0 mag) of Fbol of 3.890 ± 0.066 × 10?8 erg s?1 cm?2, and a maximum of AV = 0.1 mag solution of 4.220 ± 0.067 × 10?8 erg s?1 cm?2. The interferometric Teff is thus between 5534 ± 103 K and 5647 ± 105 K and its radius is R = 2.21 ± 0.08 R⊙. Spectroscopic measurements of HD 140283 were obtained using HARPS, NARVAL, and UVES and a 1D LTE analysis of Hα line wings yielded Teff spec = 5626 ± 75 K. Using fine-tuned stellar models including diffusion of elements we then determined the mass M and age t of HD 140283. Once the metallicity has been fixed, the age of the star depends on M, initial helium abundance Yi, and mixing-length parameter α, only two of which are independent. We derive simple equations to estimate one from the other two. We need to adjust α to much lower values than the solar one (～2) in order to fit the observations, and if AV = 0.0 mag then 0.5 ≤ α ≤ 1. We give an equation to estimate t from M, Yi (α), and AV. Establishing a reference α = 1.00 and adopting Yi = 0.245 we derive a mass and age of HD 140283: M = 0.780 ± 0.010 M⊙ and t = 13.7 ± 0.7 Gyr (AV = 0.0 mag), or M = 0.805 ± 0.010 M⊙ and t = 12.2 ± 0.6 Gyr (AV = 0.1 mag). Our stellar models yield an initial (interior) metal-hydrogen mass fraction of [Z/X]i = ?1.70 and log g = 3.65 ± 0.03. Theoretical advances allowing us to impose the mixing-length parameter would greatly improve the redundancy between M, Yi, and age, while from an observational point of view, accurate determinations of extinction along with asteroseismic observations would provide critical information allowing us to overcome the current limitations in our results.
关键词： stars: fundamental parameters,techniques: spectroscopic,surveys,stars: individual: HD 140283,techniques: interferometric,stars: Population II
更新于2025-09-19 17:15:36
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Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields
摘要： We report on the appearance of a structure at low energies in the photoelectron momentum distribution of the hydrogen atom exposed to two-color counterrotating bicircular laser fields. These structures, which arise due to ac-Stark-shifted resonances, break the threefold symmetry, typical for the ω ? 2ω bicircular fields. We discuss the physical origin of this structure in terms of partial-wave interference between direct ionization channels and a resonant pathway, which passes through the ac-Stark-shifted state, and show how the underlying Rydberg state population depend on the field strength and pulse duration.
关键词： bicircular laser fields,Rydberg state population,ac-Stark-shifted resonances,photoelectron momentum distribution,hydrogen atom
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Transferring the Record p-type Si POLO-IBC Cell Technology Towards an Industrial Level
摘要： The focus of this paper was on finding wrist sensor-derived features for detecting highly acute fall risk from the sit-to-stand transitions performed in a non-ambulatory environment. Furthermore, the influence of the dominant and non-dominant hand on these features was investigated. A cohort of 174 older subjects was monitored for seven consecutive days in their home setting by using inertial sensors attached at the wrist. Based on the reported falls during a one-month follow-up phase, two groups were defined. Twenty-one time and frequency domain features were implemented for the quantitative assessment of extracted sit-to-stand transitions. The statistical analysis yielded two features that could convincingly distinguish fallers from non-fallers for the dominant hand, and six for the non-dominant hand. A novel feature, energy of the applied support during standing up, showed statistically good performance independently of on which hand the sensor node was worn, as well as for the dominant and non-dominant hand (p < 0.014, p < 0.027, and p < 0.020, respectively). This paper overcomes limitations of clinical tests and shows a reliable application of wrist-worn bands in terms of assessment of highly acute fall risk. In addition, it reveals the sit-to-stand transition as a potential assessment source for the wrist-worn devices in the elderly population. Early assessment of the risk of falling in a widely accepted and non-stigmatized manner has the ability to bring crucial changes in fall prevention strategies, reducing the number of falls and the fall rate.
关键词： fall risk assessment,inertial sensors,transitions in daily activities,Elderly population
更新于2025-09-19 17:13:59
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[IEEE 2019 SBFoton International Optics and Photonics Conference (SBFoton IOPC) - Sao Paulo, Brazil (2019.10.7-2019.10.9)] 2019 SBFoton International Optics and Photonics Conference (SBFoton IOPC) - Advances in the prevention and monitoring of root dentin demineralization using lasers
摘要： Computational models are useful for quantitative elucidation of the dynamical behavior of biological systems. Oftentimes, several competing models (i.e., hypotheses) are proposed to describe the underlying molecular mechanisms of a biological system. Selecting the most representative model is imperative for obtaining meaningful quantitative insights into the dynamics of the system of interest. However, the discrimination between competing models poses a significant challenge due to heterogeneity that is intrinsic to biological systems. This letter demonstrates the effectiveness of a probabilistic approach to optimal experiment design for model discrimination in the presence of time-invariant cell-to-cell differences within a cell population. The JAK2/STAT5 signaling pathway, which is involved in proliferation and differentiation of hematopoietic stem cells, is used as a case study.
关键词： model discrimination,Design of experiments,population heterogeneity
更新于2025-09-16 10:30:52
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[IEEE 2019 Joint Conference of the IEEE International Frequency Control Symposium anEuropean Frequency and Time Forum (EFTF/IFC) - Orlando, FL, USA (2019.4.14-2019.4.18)] 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum (EFTF/IFC) - A Versatile Testbed for CubeSat Atomic Clock Development: EOM vs Laser Current Modulation
摘要： Atomic clocks for compact satellite missions have limitations on size, weight, and power (SWaP), while requiring ever greater levels of frequency stability and accuracy. To aid in the development of next-generation low SWaP Coherent Population Trapping (CPT) clocks, we are developing a CubeSat Atomic Clock Testbed (CuSACT). This testbed will give us the capability to vary single aspects of CPT-clock design while keeping all others constant. In this presentation, we will provide an overview of CuSACT, and discuss our preliminary results comparing direct injection-current modulation of a VCSEL with electro-optic phase modulation of the VCSEL.
关键词： vapor-cell atomic clock,coherent population trapping,Rb clock,frequency modulation,electro-optic modulation,VCSEL,optical sidebands
更新于2025-09-16 10:30:52
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Enhanced Coherent Emission from Ionized Nitrogen Molecules by Femtosecond Laser Pulses
摘要： The forward emission spectra were experimentally measured for ionized nitrogen molecules by an 800-nm pump laser and a delayed seed laser. It was found that emission lines around both 428 nm and 391 nm are greatly enhanced with injecting either a 391-nm or 428-nm seed laser. The emission lines around 391 nm and 428 nm can be assigned to the rotational transitions of N2+ (B2Σu+, v'=0 → X2Σg+, v=0) and N2+ (B2Σu+, v'=0 → X2Σg+, v=1), respectively. They origin from seed-induced superfluorescence and resonant stimulated Raman scattering. The genetic algorithm was utilized to simulate the experimental observations and determine the relative population of B2Σu+(v'=0), X2Σg+(v=1) and X2Σg+(v=0). The result verifies that the vibrational population inversion is achieved between B2Σu+(v'=0) and X2Σg+(v=0) by the 800-nm pump laser. Our finding provides new insights into controlling the coherent emission of ionized nitrogen molecules, which has promising application in filamentation-based remote atmospheric sensing.
关键词： femtosecond laser pulses,ionized nitrogen molecules,coherent emission,population inversion,superfluorescence,stimulated Raman scattering
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Population Lensing in Alexandrite Lasers
摘要： Alexandrite (Cr3+:BeAl2O4) is a vibronic laser at 701-858 nm. Its excellent thermo-mechanical properties and high energy storage make it an ideal high power and high energy Q-switched source with recent development in mJ-level red-diode-pumped Alexandrite oscillators and amplifiers [1-3]. Further power scaling of these systems is limited by thermal lensing which has yet to be addressed in great detail. In this work we present experimental and finite element analysis (FEA) results on the investigation of thermal lensing in a red-diode-pumped Alexandrite laser. Differences in the thermal lensing power for non-lasing and lasing conditions are attributed to a ‘population lens’ effect. In a separate study stable self-Q-switching (SQS) is observed in an Alexandrite laser cavity containing only the gain medium where the SQS loss mechanism is attributed to the population lens.
关键词： self-Q-switching,diode-pumped,population lens,thermal lensing,Alexandrite
更新于2025-09-12 10:27:22
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Colour Reproduction in Electronic Imaging Systems (Photography, Television, Cinematography) || Light Amplification in Lasers
摘要： In physics, specifically statistical mechanics, a population inversion occurs when a system (such as a group of atoms or molecules) exists in a state with more members in an excited state than in lower energy states. The concept is of fundamental importance in laser science because the production of a population inversion is a necessary step in the workings of a standard laser.
关键词： Boltzmann distribution,stimulated emission,population inversion,statistical mechanics,laser
更新于2025-09-11 14:15:04
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Thermal phase fluctuations in optically pumped dual-frequency vertical external-cavity surface-emitting lasers for cesium clocks based on coherent population trapping
摘要： A fully analytical model is established for the thermal fluctuations of the beatnote phase of an optically pumped dual-frequency vertical-external-cavity surface-emitting laser (VECSEL). This model starts with the resolution of the heat equation inside the semiconductor chip structure and follows with the evaluation of the induced thermo-optic phase shift. Both the fluctuations of the heat induced by the optical pumping and the thermodynamic fluctuations at room temperature are considered. On the one hand, the thermal response of the structure is investigated and a significant thermal lens effect caused by the pump is deduced. On the other hand, the power spectral density of the frequency noise is calculated in the presence of diffusion spatial anisotropy. The present model is in very good agreement with the phase noise measured for a dual-frequency VECSEL at 852 nm for application to metrology and the validity of the usual low-pass filter model is discussed.
关键词： coherent population trapping,vertical external-cavity surface-emitting lasers,optically pumped,thermal phase fluctuations,cesium clocks,dual-frequency
更新于2025-09-11 14:15:04