分类: 物理学 >> 核物理学 提交时间: 2023-06-20
摘要: Two-nucleon momentum correlation functions are investigated for different single thermal sourcesat given initial temperature (T ) and density (). To this end, the evolutions of various singleexcited nuclei at T = 1 20 MeV and = 0.2 - 1.2 0 are simulated using the thermal isospindependent quantum molecular dynamics (T hIQMD) model. Momentum correlation functions ofidentical proton-pairs (Cpp(q)) or neutron-pairs (Cnn(q)) at small relative momenta are calculatedby Lednick y and Lyuboshitz analytical method. The results illustrate that Cpp(q) and Cnn(q) keepsensitivities to the source size (A) at lower T or higher , but almost not at higher T or lower . Andthe sensitivities become stronger for smaller source. Moreover, the T , and A dependencies of theGaussian source radii are also extracted by fitting the two-proton momentum correlation functions,and the results are consistent with the above conclusions.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The combination of grating-based frequency-selective optical feedback mechanisms, such as distributed feedback (DFB) or distributed Bragg reflector (DBR) structures, with quantum dot (QD) gain materials is a main approach towards ultra-high-performance semiconductor lasers for many key novel applications, either as stand-alone sources or as on-chip sources in photonic integrated circuits. However, the fabrication of conventional buried Bragg grating structures on GaAs, GaAs/Si, GaSb and other material platforms have been met with major material regrowth difficulties. We report a novel and universal approach of introducing laterally coupled dielectric Bragg gratings to semiconductor lasers that allows highly controllable, reliable and strong coupling between the grating and the optical mode. We implement such a grating structure in a low-loss amorphous silicon material alongside GaAs lasers with InAs/GaAs QD gain layers. The resulting DFB laser arrays emit at pre-designed 0.8 THz LWDM frequency intervals in the 1300 nm band with record performance parameters, including side mode suppression ratios as high as 52.7 dB, continuous-wave output power of 27.7 mW (room-temperature) and 10 mW (at 70{\deg}C), and ultra-low relative intensity noise (RIN) of < -165 dB/Hz (2.5-25 GHz). The devices are also capable of operating isolator-free under very high external reflection levels of up to -12.3 dB whilst maintaining the high spectral and ultra-low RIN qualities. These results validate the novel laterally coupled dielectric grating as a technologically superior and potentially cost-effective approach for fabricating DFB and DBR lasers free of their semiconductor material constraints, thus universally applicable across different material platforms and wavelength bands.
分类: 物理学 >> 核物理学 提交时间: 2016-08-31
摘要: The quality of PMT signal is one of the key items for a large and high precision neutrino experiment, like Daya Bay, JUNO, while most of the experiments are affected by the PMT signal overshoot from its positive HV-single cable scheme. For JUNO prototype detector, we have a detailed study on the PMT overshoot and successfully reduced the ratio of overshoot amplitude to signal to ~1% from previous typical ~10%, with no affection to PMT other parameters. Furthermore, we calculated that the overshoot is a result of discharging of capacitors in the HV-signal splitter and the PMT voltage divider. The study result is extremely important for JUNO and other similar experiments.
分类: 核科学技术 >> 核科学与技术 提交时间: 2024-01-06
摘要: POLAR-2 is a gamma-ray burst (GRB) polarimeter that is designed to study the polarization in GRB radiation emissions, aiming to improve our knowledge of related mechanisms. POLAR-2 is expected to utilize an on#2;board polarimeter that is sensitive to soft X-rays (210 keV), called low-energy polarization detector (LPD). We have developed a new soft X-ray polarization detector prototype based on gas microchannel plates (GMCPs) and pixel chips (Topmetal). The GMCPs have bulk resistance, which prevents charging-up effects and ensures gain stability during operation. The detector is composed of low-outgassing materials and is gas-sealed using a laser welding technique, ensuring long-term stability. A modulation factor of 41.28% 0.64% is obtained for a 4.5 keV polarized X-ray beam. A residual modulation of 1.96% 0.58% at 5.9 keV is observed for the entire sensitive area.