共查询到20条相似文献,搜索用时 46 毫秒
1.
光子带隙是指某一频率范围的波不能在周期变化的空间介质中传播,即这种结构本身存在“禁带”,并已成功地应用于滤波器、放大器和混频器等器件的设计中.此前,许多专家都致力于提高带隙的反射率,但其只能逐渐接近1.本文在囚禁于一维光晶格中的冷原子介质中实现两个可调光子带隙,并通过选择两基态为精细结构的三能级∧型原子系统,考虑自发辐射相干效应来探究这两个带隙的反射率.适当调节参数,探测场出现增益,从而获得较高反射率的带隙结构,甚至可以超过1.此外,两个带隙反射率还可以通过调节偶极矩之间的夹角以及非相干驱动场强度等参数来操控. 相似文献
2.
Sulagna Dutta 《Molecular physics》2013,111(8):431-443
A new approach is suggested to realize simultaneous negative permittivity and permeability in a three level closed system with incoherent pumping via spontaneously generated coherence (SGC). In this system the negativity of the real part of magnetic permeability can be achieved in the presence of SGC whereas in the absence of SGC it is positive. Thus the SGC makes the system a negative index medium (NIM) in a band of frequency range. The position and the band of the frequency region of negative refraction can be manipulated by controlling the incoherent pump rate. We achieve FOM?=?7.91165. We have studied the group index in the negative refractive index region and have shown that the group velocity switches from superluminal to subluminal mode in this region of negative refraction. We have shown that the negative refractive index can be realized in a heteronuclear molecule. 相似文献
3.
LI Jia-Hua YANG Wen-Xing PENG Ju-Cun 《理论物理通讯》2004,42(9)
We discuss and analyze the absorption-amplification properties of a weak probe field in a typical four-level atomic system in the presence of an additional coherence term, the spontaneously generated coherence term. Theinfluences of the spontaneously generated coherence and a coherent pump field on the probe absorption (amplification)are investigated in detail. We show that the absorption of such a weak probe field can be dramatically enhanced dueto the presence of the spontaneously generated coherence. At the same time, the probe-absorption profile exhibitsthe double-peak structure and the probe-absorption peak gradually decreases as the pump intensity increases. On thecontrary, the amplification of such a weak probe field near the line center of the probe transition can be achieved byadjusting the coherent pump field intensity in the absence of the spontaneously generated coherence. 相似文献
4.
研究驻波场相干驱动下四能级双Lamder模型的电磁感应光子带隙.当耦合场是远共振或共振时,来自于两邻近能级间的自发辐射相干效应(SGC)有助于实现一个或两个光子带隙.当自发辐射相干效应不存在时,探测场被原子系统强烈吸收,因此导致光子带隙严重形变甚至无法形成.数值结果表明,光子带隙结构是由SGC效应导致探测场和耦合场之间的相干增强Kerr非线性调制而产生,并改变驻波场的耦合方式,使系统实现单光子带隙转变为双光子带隙的动态调控. 相似文献
5.
研究驻波场相干驱动下四能级双Lamder模型的电磁感应光子带隙。当耦合场是远共振或共振时,来自于两邻近能级间的自发辐射相干效应(SGC)有助于实现一个或两个光子带隙。当自发辐射相干效应不存在时,探测场被原子系统强烈吸收,因此导致光子带隙严重形变甚至无法形成。数值结果表明,光子带隙结构是由SGC效应导致探测场和耦合场之间的相干增强Kerr非线性调制而产生,并改变驻波场的耦合方式,使系统实现单光子带隙转变为双光子带隙的动态调控。 相似文献
6.
Dynamically controlled optical nonreciprocity of a double-ladder system with spontaneously generated coherence in moving atomic optical lattice 下载免费PDF全文
A four-level double-ladder cold atoms system with spontaneously generated coherence trapped in a moving optical lattice is explored to achieve optical nonreciprocity. When spontaneously generated coherence(SGC) is present, the remarkable contrast optical nonreciprocity of light transmission and reflection can be generated at each induced photonic bandgap in the optical lattice with a velocity of a few m/s. However, when the SGC effect is absent, the optical nonreciprocity becomes weak or even vanishing due to the strong absorption. It is found that the optical nonreciprocity is related to the asymmetric Doppler effect in transmission and reflection, meanwhile the degree and position of optical nonreciprocity can be tuned by the SGC effect and the Rabi frequency of the trigger field. 相似文献
7.
8.
Influence of Doppler broadening and spontaneously generated coherence on propagation effect in a quasi lambda-type four-level system 下载免费PDF全文
In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the Doppler broadening is present, generally speaking, the values of gain and intensity of lasing without inversion (i.e. the probe field) in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case; considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength. The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength; when spontaneously generated coherence is present, much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained. Choosing suitable values of the probe detuning, Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion. 相似文献
9.
Si-Cong Tian Zhi-Hui Kang Chun-Liang Wang Ren-Gang Wan Jun Kou Hang Zhang Yun Jiang Hai-Ning Cui Jin-Yue Gao 《Optics Communications》2012,285(3):294-299
We report the experimental observation of the effect of spontaneously generated coherence on absorption without the rigorous requirement of close-lying levels. The experiments are studied in both a four-level N-type and a four-level inverted-Y-type atomic system in a rubidium atomic beam. With the coupling and controlling field, the N-type system is equivalent to a system with three closely upper levels coupled to one lower level by the same vacuum modes. The quantum interference can induce two prominent and nearly transparent holes where the slope of the refractive index is very steep. This special situation could allow the simultaneous propagation of two weak pulses with different frequencies. When we tune the wavelength of the controlling field, the N-type system turns to be the inverted-Y atomic system. Under the two-photon resonance condition, the system is equivalent to a V-type system with two closely upper levels, and the interference can reduce one broad transparency window in the middle of the absorption spectrum. Besides we can control the number of the spontaneously decay channels by the detuning of the controlling field, thus the effect of spontaneously generated coherence can exist in three or two closely space levels. 相似文献
10.
Xiang-an Yan Li-qiang Wang Wen-juan Jiang Jian-ping Song Yan-peng Zhang 《Physics letters. A》2008,372(42):6456-6460
We propose a scheme for giant enhancement of the Kerr nonlinearity in a four-level atomic system in which spontaneously generated coherence is present. The physics mechanism of the enhancement of Kerr nonlinearity is mainly based on the presence of an extra atomic coherence induced by the spontaneously generated coherence. Numerical values obtained by solving the density matrix equations agree well with these exact analytical values. 相似文献
11.
12.
S. -C. Zhao 《JETP Letters》2011,94(5):347-352
A theoretical investigation is carried out into the effect of spontaneously generated coherence (SGC) on the left-handedness
in a four-level Y-type atomic system with two highest nearly degenerate lying levels. It is found, with the spontaneously generated coherence
intensity enhancing, the atomic system gradually displays left-handedness with simultaneous negative permittivity and permeability.
And the refractive index enhances with the increasing intensity of SGC. However, the absorption is suppressed by the SGC effect
when the SGC has a large intensity. When the probe field is near-resonant coupled to the atomic system, the appearance of
SGC doesn’t always change the permeability from positive to negative and allow for lefthanded behavior, unless the SGC reaches
a large intensity. 相似文献
13.
Enhanced Kerr nonlinearity in a left-handed three-level atomic system driven by a bichromatic field 下载免费PDF全文
Enhanced Kerr nonlinearity in a left-handed atomic system consisting of three levels driven by a bichromatic field is presented in this paper.Based on bichromatic field coherence,the real parts of the permittivity and permeability can obtain negative values simultaneously in the same detuning frequency region.By adjusting the frequency difference and the Rabi frequencies of the bichromatic field,the multi-band left-handed behavior of the presented atomic metamaterial is exhibited.Meanwhile,the enhanced Kerr nonlinearity can be realized in this multi-band left-handed three-level atomic system.It is shown that the third-order susceptibility possesses focusing or defocusing properties in the same frequency band. 相似文献
14.
For a V-type three-level atomic system with two closely spaced upper levels, we investigate the light pulse propagation properties with only one laser field. Due to spontaneously generated coherence, the group velocity of the light pulse can be changed from subluminal to superluminal. The effects of the field intensity and the two-upper level splitting on the group velocity are also shown. At last, an analytical expression for the group velocity is given in the case of a weak field. 相似文献
15.
HAN Ding-An GUO Hong BAI Yan-Feng SUN Hui ZENG Ya-Guang 《理论物理通讯》2006,46(4):731-734
For a V-type three-level atomic system with two closely spaced upper levels, we investigate the light pulse propagation properties with only one laser field. Due to spontaneously generated coherence, the group velocity of the light pulse can be changed from subluminal to superluminal. The effects of the field intensity and the two-upper level splitting on the group velocity are also shown. At last, an analytical expression for the group velocity is given in the case of a weak field. 相似文献
16.
The effect of spontaneously generated coherence on the probe response in an open ladder atomic system with equispaced levels is studied. The result shows that by adjusting the strength of spontaneously generated coherence (SGC), electromagnetically induced transparency (EIT) and high dispersion (index of refraction) with zero absorption can be realized, a much larger gain without inversion (GWI) than that without SGC can be obtained. Moreover, in the open system and for some strength of SGC, GWI without the incoherent pumping is much larger than that with the incoherent pumping; however, in the corresponding closed system, when the incoherent pumping is absent, we cannot obtain any gain (with or without inversion) for any strength of SGC. In addition, the manipulation role of the atomic exit and injection rates on SGC-dependent absorption property is analyzed for the case when the incoherence pumping does not exist. 相似文献
17.
Phase-dependent inversionless gain in a four-level atomic system with a closed interaction loop 下载免费PDF全文
A four-level atomic system with a closed interaction loop connected
by two coherent driving fields and a microwave field is
investigated. The results show that inversionless gain can be
achieved on a higher frequency transition outside the closed
interaction loop, and the gain behaviour can be modulated by the
phase of the closed loop as well as the amplitude of the microwave
field. The phase sensitivity property in such a scheme is similar to
that in an analogous configuration with spontaneously generated
coherence, but it is beyond the rigorous condition of
near-degenerate levels with non-orthogonal dipole moments.
Therefore this scheme is much more convenient in experimental
realization. 相似文献
18.
We investigate the nonlinear optical phenomena of the optical bistability and multistability via spontaneously generated coherence in an asymmetric double quantum well structure coupled by a weak probe field and a controlling field. It is shown that the threshold and hysteresis cycle of the optical bistability can be conveniently controlled only by adjusting the intensity of the SGC or the controlling field. Moreover, switching between optical bistability and multistability can be achieved. These studies may have practical significance for the preparation of optical bistable switching device. 相似文献
19.
A three-level atomic system in V-configuration (interacting with a single mode laser field) with parallel
transition dipole moments exhibiting spontaneously generated coherence due to quantum interference of
decaying channels is considered here for the purpose of storing light pulses. This system is equivalent to
(with some restrictions) another three-level system in which ground state is coupled with one of the upper
states but the upper states are coupled through a DC field and hence can be used to store electromagnetic
pulse using the concept of dark-state-polariton. 相似文献
20.
We have theoretically studied the effects of quantum coherence in a driven quasi-degenerate two-level atomic system. We have shown that the quantum interference, which can be destructive or constructive, can be controlled by an externally applied magnetic field allowing one to implement both electromagnetically induced transparency and electromagnetically induced absorption in the same atomic system. Determined by frequency dispersion of the index of refraction of the system, the group velocity of light pulses ranges from ultra-slow to superluminal with changing of the magnitude of the magnetic field. 相似文献