分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We propose a magnetic laser in a subwavelength system consisting of a high-refractive-index dielectric cavity and an active medium formed by magnetic quantum emitters. Stimulated emissions of magnetic quantum emitters induced by their coherent interactions with quantized magnetic fields of a cavity are theoretically considered. The condition to archive such a magnetic laser is obtained. Numerical results show that magnetic lasers are feasible in some realistic systems, for example, a silicon disk of high-quality whispering gallery modes with embedded emitters. Furthermore, the competitions between the electric interaction and magnetic one in terms of their Purcell factors are also considered in some magnetic laser achievable systems. In a wavelength-scale silicon block of a high-order magnetic mode, the ratio of magnetic Purcell factor to the electric one can reach more than ~103 large. Our results open up ways to enhanced magnetic light-matter interactions.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The interaction of magnetic dipole (MD) emitters and common photonic cavities is usually weak, which is partially due to the low magnetic near field enhancements of the cavities. Here, we show that whispering gallery modes (WGMs) of a subwavelength dielectric cavity can not only greatly boost the emission rate of a MD emitter but also bring efficient couplings between coherent MD emitters. In a WGM cavity, the maximal emission rate ({\gamma}max) of a single emitter occurs at an antinode of the field pattern. The emission of the MD emitter can also be greatly affected by another coherent one depending on the magnetic field response of the WGM. The maximal contribution can also reach {\gamma}max. Notably, the cooperative emission rate of the coherent MD emitters does not decay with distance in the considered range due to the high-quality feature of a WGM. In contrast to the emission, the absorption of an emitter is hardly affected by the coherent couplings between emitters mediated by a WGM. The difference between the performances of emission and absorption is highly related to the excitation behaviors of WGMs. Our results are important for enhanced magnetic light-matter interactions.
分类： 物理学 >> 核物理学 分类： 核科学技术 >> 核科学与技术 分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2024-01-08
摘要： To detect radioactive substances with low activity levels, an anticoincidence detector and a high-purity germanium (HPGe) detector are typically used simultaneously to suppress Compton scattering background, thereby resulting in an extremely low detection limit and improving the measurement accuracy. However, the complex and expensive hardware required does not facilitate the application or promotion of this method. Thus, a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector, whereby Compton scattering background is suppressed and a low minimum detectable activity (MDA) is achieved without using an expensive and complex anticoincidence detector and device. The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location, as well as the characteristics of energy-deposition distributions for full- and partial-energy deposition events. This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification. To accurately determine the relationship between the deposited energy of gamma rays in the detector and the deposition location, we extract four shape parameters from the pulse signals output by the detector. Machine learning is used to input the four shape parameters into the detector. Subsequently, the pulse signals are identified and classified to discriminate between partial- and full-energy deposition events. Some partial-energy deposition events are removed to suppress Compton scattering. The proposed method effectively decreases the MDA of an HPGe -energy dispersive spectrometer. Test results show that the Compton suppression factors for energy spectra obtained from measurements on 152Eu, 137Cs, and 60Co radioactive sources are 1.13 (344 keV), 1.11 (662 keV), and 1.08 (1332 keV), respectively, and that the corresponding MDAs are 1.4%, 5.3%, and 21.6% lower, respectively
分类： 物理学 >> 核物理学 提交时间： 2023-12-07
摘要： To detect radioactive substances with a low activity level, an anti-coincidence detector and high-purity germanium detector (HPGe) are often used in combination to suppress the Compton scattering background, thereby obtaining an extremely low detection limit and improving the measurement accuracy. However, the complex and expensive hardware system required does not facilitate application and promotion of this method. Thus, a method is proposed to discriminate the digital waveform of pulse signals output by a HPGe detector, whereby the Compton scattering background is suppressed and a low minimum detectable activity (MDA) is obtained without using an expensive and complex anti-coincidence detector and device. The electric field strength distribution and the energy deposition distribution in the detector are simulated to determine the relationship between the pulse shape and location of energy deposition, as well as the characteristics of the energy deposition distribution for full- and partial-energy deposition events. This relationship is used to develop a pulse shape discrimination (PSD) algorithm based on employing an artificial neural network (ANN) for pulse feature identification. To accurately determine the relationship between the deposited energy of gamma (g)-rays in the detector and deposition location, we extract four shape parameters from the pulse signals output by the detector. Machine learning is used to input the four shape parameters to the detector. Then, the pulse signals are identified and classified to discriminate between partial- and full-energy deposition events, and some partial-energy deposition events are removed to suppress Compton scattering. The proposed method effectively lowers the MDA of a HPGe -energy dispersive spectrometer. Test results show that the Compton suppression factors for energy spectra obtained from measurements on 152Eu, 137Cs and 60Co radioactive sources are 1.13 (344 keV), 1.11 (662 keV) and 1.08 (1332 keV), respectively, and the corresponding MDAs are lowered by 1.4%, 5.3% and 21.6%.
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