分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-07-05
摘要: Whether the speed of light at the surface of rotating Earth is isotropic or not is both an important theoretical problem and one that has significant implications for scientific practices. Especially the unit of length, a meter, is defined as the length of the path travelled by light in vacuum in 1/299792458 of a second, on the basis that the speed of light is constant, c = 299792458 m/s. By applying the GPS range equation whose correctness has been fully verified by GPS practices, we found that the speed of light on rotating Earth's surface is neither constant nor isotropic, but rE c' c v d , where rE v is the local linear velocity of Earth's rotation, and d is the unit vector of the light propagation's direction. It follows that the anisotropy of the speed of light at the Earth's surface has a significant impact on the definition of the meter. For example, at the equator, in 1/299792458 of a second the length of the eastward light path is 3.1 m shorter than the westward one's. Based on this, and the difference between Earth rotation's Sagnac effects on the equator and the meridian, we propose a crucial experiment to examine the anisotropy of the speed of light: let a stable pulsed laser emitting pulses in two opposite directions, use the ultrafast imaging techniques for visualizing, measuring and comparing the spacing of the pulses in opposite directions. Then we can decisively conclude whether the speed of light is anisotropic or not.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: It is critical to characterize the carrier and instantaneous frequency distribution variation in ultrafast processes, all of which are determined by the optical phase. Nevertheless, there is no method that can single-shot record the intro-pulse phase evolution of pico/femtosecond signals, to date. By analogying holographic principle in space to the time domain and using the time-stretch method, we propose the dispersive temporal holography to single-shot recover the phase and amplitude of ultrafast signals. It is a general and comprehensive technology and can be applied to analyze ultrafast signals with highly complex dynamics. The method provides a new powerful tool for exploring ultrafast science, which may benefit many fields, including laser dynamics, ultrafast diagnostics, nonlinear optics, and so on.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: We experimentally demonstrate the spontaneous synchronization and the exceptional point (EP) induced pulse generation mechanism in the breather complex. The breathing frequency and phase are found to be synchronized during the formation of a 9-breather assembled complex in a mode-locked fiber laser. The breathers are formed at exactly the time point of the complex's breathing frequency leaving or entering the subharmonic entrainment. Such new pulse generation mechanism should be related to the non-Hermitian EPs or the time translation symmetry breaking. The investigations of destroying and rebuilding the mode-locking reveal the connection between the synchronization and laser stabilization. These findings may inspire a wide range of researches including ultrafast optics, micro-cavity combs, ocean breather behaviors, non-Hermitian optics, etc.
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: A readout electronics has been developed for the silicon strip array detector system of HIRFL-CSR-ETF. It consists of 48 front end electronics (FEE) boards, 12 PXI-DAQ boards and one trigger board. It can implement energy and time measurements of 4608 channels. Each FEE board is based on 6 ASICs (ATHED), which implements energy and time measurements of 96 channels. The PXI-DAQ board meets requirements of high-speed counting and amount of readout channels and can process signals of 4 FEEs. The trigger board is developed to select the valid events. The energy linearity of the readout electronics is better than 0.3% in the dynamic range of 0.10.7 V. In the test with a standard triple alpha source, the energy resolution was 1.8% at 5.48 MeV. This readout electronics enables the silicon strip array system to identify particles of A 14.