This article gives the absolute calibration of two types phosphor screens (DRZ) that were used to detect and characterize electron bunches driven by laser-plasma accelerator. The test was performed with picoseconds electron bunch at a radio frequency linear electron accelerator in Tsinghua University. The photons emitted from DRZ screens showed good linear responses to the charge of incident electron bunch and cosine angular distribution in space. An energy conversional efficiency of effective scintillant matter was also calculated.
Spin-wave dynamics in full-Heusler Co2FeAl0.5Si0.5 films are studied using all-optical pump-probe magneto-optical polar Kerr spectroscopy. Backward volume magnetostatic spin-wave (BVMSW) mode is observed in films with thickness ranging from 20 to 100 nm besides perpendicular standing spin-wave (PSSW) mode, and found to be excited more efficiently than the PSSW mode. The field dependence of the effective Gilbert damping parameter appears especial extrinsic origin. The relationship between the lifetime and the group velocity of BVMSW mode is revealed. The frequency of BVMSW mode does not obviously depend on the film thickness, but the lifetime and the effective damping appear to do so. The simultaneous excitation of BVMSW and PSSW in Heusler alloy films as well as the characterization of their dynamic behaviors may be of interest for magnonic and spintronic applications.
In order to determine the effect of different light source’s spectrum to a subjects’ visual performance, this experiment examined three fluorescent lamps with a colour temperature of 2700K, 4000K and 6500K and an incandescent lamp. The results were compared to the average recognition rate a “reference person” from different light sources. Experimental results show significant differences in the recognition rate from different optical spectrum light source and recognition rate value. We determined the best combination of ambient and chalkboard light source and propose avoiding combination for classroom lighting that is clearly inferior. This article provides selection reference for optimal classroom ambient and blackboard lighting. In recent years, the study of psychological and physiological effect of light has become one of the most important field in lighting research[1]. Studies has shown that different light spectrum could affect human circadian rhythm, body temperature and alertness, which directly affecting work efficiency and health[2]. The effects by classroom light spectrum on efficiency and health cannot be ignored, as the students are exposed to one particular lighting environment for extended periods of time. Through a systematic survey of classroom lighting in several universities in Chongqing and Chengdu, T5 fluorescent of high colour temperature about 6500K was the predominant choice for classroom general lighting as well as blackboard lighting. Many students complained that they tired easily at this colour temperature. In another study on classroom light source[3] students’ preference for colour temperature is not fixed but varies according to classroom’s function and illuminance level. It was insufficient to choose colour temperature of classroom lighting based on the results of the above questionnaire. We therefore chose and compared T5 fluorescent lamps of 2700K, 4000K and 6500K colour temperature on the visual performance and their effects on study efficiency, asthenopia and physiological rhythm. Due to space limitations this article only discusses the contrast experiment of visual performance.
Ultrafast magnetization dynamics in GdFeCo films triggered by femtosecond laser pulses with and without an external field applied is studied experimentally for different excitation fluence. It is found that subpicosecond magnetization reversal occurs simultaneously in the ultrafast dynamics of both saturation and remnant magnetization states and almost identical within 13 ps, whereas relatively slow magnetization reversal across compensation point appears only in the dynamics of saturation magnetization state. It shows the subpicosecond magnetization reversal is external field independent, and originates from intrinsic magnetic evolution in ferrimagnetic system. The intrinsic subpicosecond reversal is qualitatively explained by linear reversal.
The influence of artificial classroom light source’s colour temperature to students’ learning efficiency and physiology rhythm is the focus of this study. An experiment compares a subjects’ learning efficiency, asthenopia and brain fag under different luminance level of three typical colour temperatures from T5 fluorescent lamps and LED. Using comprehensive index ε and norm identification Ψ for quantitative evaluation and testing under different lighting environments, we determined the best colour temperature of two experimental light sources. We also determined the best combinations of illuminance value and the colour temperature that should be avoided in classroom lighting. Experiment shows that spectrum difference obviously effects comprehensive index ε and norm identification Ψ. For learning efficiency and health of people, there need to be improvement in the spectrum of fluorescent lamps and LEDs
In this paper, we propose a new type of metal-insulator-metal (MIM) hybrid cavity compound grating micro-structure array, which can achieve dual narrowband super-absorption in the near-infrared window. The thin plasmonic microstructure effectively modulates coupling and hybridization effects between surface plasmon polaritons of different transmission resonance cavities to form designable dual narrowband resonance states to achieve near-infrared operation proving manipulation of the optical characteristics in the near-infrared light field. Furthermore, we conduct an in-depth theoretical exploration of the structure's unique properties, such as its high-quality factor, low noise, super-absorption, precise control, and the physical mechanism of its excellent performance in ambient refractive index sensing and detection. This study provides developmental insights for the miniaturization, easy modulation, and multi-function development of surface plasmon superabsorbers while broadening their application in near-infrared environment refractive index detection. The proposed microstructure is also suitable for integration with optical elements.
The temperature sensor is the core part of the temperature measurement instrument, and its performance directly determines the temperature measurement accuracy. Photonic crystal fiber (PCF) is a new type of temperature sensor with extremely high potential. In this paper, we propose a high-performance, structurally simple, liquid-filled PCF temperature sensor, which is based on a SMF-PCF-SMF (single mode fiber, SMF) sandwich structure. By adjusting the structural parameters of the the PCF, it is possible to obtain optical properties that are superior to those of ordinary optical fibers. This allows for more obvious responsive changes of the fiber transmission mode under small external temperature changes. By optimizing the basic structure parameters, a new PCF structure with a central air hole is designed, and its temperature sensitivity is -0.04696 nm/°C. When filling the air holes of PCFs with temperature-sensitive liquid materials, the response of the optical field against the temperature fluctuations can be effectively enhanced. The Chloroform solution is used to selectively infiltrate the resulting PCF owing to its large thermo-optical coefficient. After comparing various filling schemes, the calculation results show that the highest temperature sensitivity of -15.8 nm/°C is finally realized. The designed PCF sensor has a simple structure, high-temperature sensitivity, and good linearity showing great application potential.
In this paper, the generation of relativistic electron mirrors (REMs) and the reflection of an ultra-short laser off this mirrors are discussed, applying two-dimensional particle-in-cell (2D-PIC) simulations. REMs with ultra-high acceleration and expanding velocity can be produced from a solid nanofoil illuminated normally by an ultra-intense femtosecond laser pulse with a sharp rising edge. Chirped attosecond pulse can be produced through the reflection of a counter-propagating probe laser off the accelerating REM. In the electron moving frame, the plasma frequency of the REM keeps decreasing due to its rapidly expanding. The laser frequency, on the contrary, keeps increasing due to the acceleration of REM and the relativistic Doppler shift from the lab frame to the electron moving frame. Within an ultra-short time interval, the two frequencies will be equal in the electron moving frame, which leads the resonance between laser and REM. The reflected radiation near this interval and the corresponding spectra will be amplified due to the resonance. Through adjusting the arriving time of the probe laser, certain part of the reflected field could be selectively amplified or depressed, leading to the selectively adjusting of the corresponding spectra.
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