Resonant-cavity-enhanced infrared detector incorporating an ultra-thin type-II superlattice: design and simulation.

A resonant-cavity-enhanced type-II superlattice (T2SL) infrared detector based on a metal grating has been designed to address the weak photon capture and low quantum efficiency (QE) issues of T2SL infrared detectors. Simulations have been conducted to analyze the effects of metal grating parameters, including length, thickness, and incident angle, on the spectral response and absorptivity of the absorption layers in T2SL infrared detectors. By optimizing the design, an appropriate resonant cavity structure was obtained. Research results indicate that the resonant cavity structure can significantly enhance the absorption rate of a T2SL infrared detector with a 0.2 µm thick absorption layer in the 3-5 µm wavelength range, observing peak absorption rates at 3.82 µm and 4.73 µm, with values of 97.6% and 98.2%, respectively. The absorption rate of the 0.2 µm thick T2SL absorption layer at peak wavelengths increased from 6.03% and 2.3% to 54.48% and 27.91%, respectively. The implementation of the resonant-cavity-enhanced T2SL infrared detector improves the QE while reducing absorption layer thickness, thus opening up new avenues for improving T2SL detector performance.

Acoustic performance of near-rail low-height noise barriers installed on suburban railway bridges.

With the large-scale construction of suburban railway viaducts, the noise problem along the viaducts is becoming more and more prominent. Conventional vertical noise barriers have been widely used to alleviate the noise problem along the suburban railway viaducts. However, conventional vertical noise barriers often have an adverse effect on the urban landscape and also block the view of train drivers and passengers. A type of near-rail low-height noise barrier was planned to install on the viaducts of Wenzhou Rail Transit Line S1 to reduce the impact of noise on residents along the railway lines. To assess the acoustic performance of the near-rail low-height noise barrier, a numerical procedure for railway viaduct comprehensive noise considering wheel-rail noise and structure-borne noise of the bridge and noise barriers was proposed and then verified by a field test. On this basis, numerical models were established to compare the acoustic performances of the near-rail low-height noise barrier and conventional vertical noise barrier. The influences of the height and top shape of the near-rail low-height noise barrier on the acoustic performance were discussed. Based on the numerical analysis results, it is found that both the near-rail low-height noise barrier and conventional vertical noise barrier have good acoustic performances. The noise reduction effect of the near-rail low-height noise barrier is slightly better than that of the conventional vertical noise barrier. The acoustic performance of the near-rail low-height noise barrier gradually improves, but the improvement rate gradually slows down as the height of the noise barrier increases. The noise reduction effects of both the inverted L-shaped and Y-shaped near-rail low-height noise barrier are obviously better than that of the vertical one, while the noise reduction effects of the inverted L-shaped near-rail low-height noise barrier are slightly better than the Y-shaped one.

Experimental study on the characteristics of train-induced vibration in a new structure of metro depot.

In order to improve the utilization rate of expensive and very limited urban land, a new structure system, underground metro depot, has been developed and applied in several cities in China. The underground metro depot, which is built underground, can be multiple stories, and allows other developments on top, has become increasingly popular in recent years. Since there are other developments on top, the vibration induced by the trains frequently entering and exiting the depot cannot be ignored. To better understand the characteristics of the train-induced vibration in the underground metro depot, a series of field tests were conducted on a two-story underground depot which is the largest underground metro depot in Asia. The results show that the main frequency components of vibration source are between 50 and 200 Hz and the level of that in the first floor underground is larger than that in the second floor underground due to the train floor structure interaction when the train running on the first floor underground. The vibration in the top platform decreases linearly with the distance from the measuring point to the center line of the track. When the train is running on the track at the edge area, the linear attenuation rate was about 0.2dB/m. It is easy to excite the vibration mode of the floor structure when the train is running on the first floor underground, so the vibration in the top platform induced by the train running on the first floor underground was much larger than the train running on the second floor underground. In the future design, if the underground depot has more than one floor, the structural dynamic behavior of over-track buildings induced by the train running on the floor slab underground should be the focus. The throat area has many rail joints and turnouts which can lead to a larger vibration level, the level easy to exceed the limit given for human vibration comfort. If developments are proposed on top of the throat area, the vibration level should be carefully checked in the area within 30 m from the track to avoid potential later vibration problem.

Stimulated Brillouin scattering of backward stimulated Raman scattering.

The rescattering of backward stimulated Raman scattering (BSRS) by stimulated Brillouin scattering (SBS) is found in the high electron density region by relativistic Vlasov-Maxwell simulation and particle-in-cell (PIC) simulation, where the BSRS is in the regime of absolute instability and dominates in all the scatterings. Both one dimension (1D) Vlasov simulation and two dimension (2D) PIC simulation have been given to verify that there exists SBS of BSRS in the regime of absolute instability for BSRS. The SBS of BSRS will be even stronger than forward stimulated Raman scattering (FSRS) and SBS in regime of absolute instability for BSRS. Thus, besides Langmuir decay instability and laser energy absorption, the SBS of BSRS is also an important saturation mechanism of BSRS in high electron density region.