GaN量子点基于电磁感应透明的慢光效应

通过分析介质的有效复极化率,研究了GaN球形量子点基于电磁感应透明(EIT)的慢光效应.分别用一带和六带有效质量理论计算了GaN量子点的能级结构,模拟了探测光的吸收谱、色散谱以及放慢因子随耦合光强的变化,并考虑了失相率和耦合光失谐对放慢因子的影响.研究结果表明,慢光因子存在最大值,取最大值时所对应的耦合光强与失相率相关,耦合光越强电磁感应透明现象越明显,耦合光失谐不影响放慢因子的大小.     

Laser frequency locking based on Rydberg electromagnetically induced transparency

We present a laser frequency locking to Rydberg transition with electromagnetically induced transparency(EIT)spectra in a room-temperature cesium vapor cell. Cesium levels 6S_(1/2), 6P_(3/2), and the n D_(5/2) state, compose a cascade three-level system, where a coupling laser drives Rydberg transition, and probe laser detects the EIT signal. The error signal, obtained by demodulating the EIT signal, is used to lock the coupling laser frequency to Rydberg transition. The laser frequency fluctuation, ~0.7 MHz, is obtained after locking on, with the minimum Allan variance to be 8.9 × 10~(-11).This kind of locking method can be used to stabilize the laser frequency to the excited transition.     

固体材料中原子相干效应的研究进展

原子相干效应是光与物质相互作用的结果,它导致了一系列重要的物理现象。目前原子相干的实验研究工作主要在原子气体中开展,而与之相比固体材料中的相关实验研究具有更实际的应用前景。本文系统介绍了近年来固体材料中原子相干效应的研究进展,主要涉及电磁感应光透明、光速减慢与相干存储、存储光信息的可控制擦除、基于光存储的全光路由、双光脉冲的速度减慢和可逆存储和基于原子相干的增强四波混频等基本内容,最后还讨论了其在相关领域的应用。     

线性色散理论描述内腔EIT介质的正交模式分裂

正交模分裂(或真空Rabi分裂)是原子与光学腔构成的复合系统实现强相互作用的一个典型现象.本文理论研究了三能级原子介质与腔构成的复合系统,利用线性色散理论将腔内三能级原子自感应透明(EIT)介质的吸收和色散引入光学腔透射公式,非常直观清晰得到腔透射谱的三个分裂峰,它是由腔内EIT介质的吸收和色散特性使一个共振腔模分裂为三个腔模.该方法可以推广到腔内含有任意色散和吸收的介质.     

Quantitative measurement of solids distribution in gas–solid riser flows using electrical impedance tomography and gamma densitometry tomography

An electrical impedance tomography (EIT) system has been developed to non-invasively measure particle distributions in the riser of a pilot-scale circulating fluidized bed (CFB). Although EIT systems have often been applied to yield qualitative information about gas–solid flows, the present EIT system yields quantitative information that is validated by comparison to a gamma densitometry tomography (GDT) system. EIT and GDT were applied to the CFB riser (14-cm inner diameter, 5.77-m height) containing fluid catalytic cracking particles in air. The flows examined were annular with a dilute core and had average and near-wall solids volume fractions up to 0.25 and 0.66, respectively. For all cases, the average and near-wall solids volume fractions from EIT and GDT agreed to within 0.03 and 0.07, respectively. This good agreement suggests that, where feasible, EIT can be used in place of GDT, which is advantageous since EIT systems are often safer, less expensive, and faster than GDT systems.     

Reflection-type electromagnetically induced transparency analogue in terahertz metamaterials

A reflection-type electromagnetically induced transparency（EIT） metamaterial is proposed, which is composed of a dielectric spacer sandwiched with metallic patterns and metallic plane. Experimental results of THz time domain spectrum（THz-TDS） exhibit a typical reflection of EIT at 0.865 THz, which are in excellent agreement with the full-wave simulations. A multi-reflection theory is adopted to analyze the physical mechanism of the reflection-type EIT, showing that the reflection-type EIT is a superposition of multiple reflection of the transmission EIT. Such a reflection-type EIT provides many applications based on the EIT effect, such as slow light devices and nonlinear elements.     

Long wavelength infrared photodetector design based on electromagnetically induced transparency

A novel long-wavelength infrared (IR) photodetector based on Electromagnetically induced transparency (EIT) which is suitable for operation in about room temperature and THz range is proposed and analyzed in detail in this article. The main point in this paper for operation in room temperature is related to convert the incoming long-wavelength IR signal to short-wavelength or visible probe optical field through EIT phenomena. For realization of the idea, we used 4, 5- and 6-level atoms implemented by quantum wells or dots. In the proposed structure long-wavelength IR signal does not interact directly with electrons, but affects the absorption characteristics of short-wavelength or visible probe optical field. Therefore, the proposed structure reduces and cancels out the important thermionic dark current component. So, the proposed idea can operate as long wavelength photodetector.     

Absorption spectroscopy of cold caesium atoms confined in a magneto-optical trap

Absorption spectra of cold caesium atoms confined in a magneto-optical trap are measured around D_2 line at 852nm with a weak probe beam. Absorption reduction dip due to electromagnetically induced transparency (EIT) effect induced by the cooling/trapping field in a V-type three-level system and a gain peak near the cycling transition are clearly observed. Several mechanisms mixed with EIT effect in a normal V-type three-level system are briefly discussed. A simple theoretical analysis based on a dressed-state model is presented for interpretation of the absorption spectra.