Double-dark resonance

In this present article, we will give a brief review of some of our recent research work related to atomic localization via the effects of atomic coherence and quantiun interferences atom localization based on double-dark resonance effects [23,24], sub-half-wavelength local ization via two standing-wave fields [27], as well as its application in atom nano-lithograph[28]. Then we will introduce some of our recent related work in quantum well systems[62,63]. 

Atom localization based on double-dark resonance effects... 

Double-dark resonances have been demonstrated in a variety of four-level systems [39-50], where the probe absorption spectrum is characterized by two HIT windows, separated by a sharp absorption peak [51]. The appearance of the central narrow structure is due to the coherent interaction between the two dark states [39], which greatly enhances the Kerr nonlinear susceptibility [55]. In this section, we present our atom localization schemes based on double-dark resonance effects in two different four-level atomic systems. 

From Eqs. (3)-(5), it is easy to see that the behavior of atom localization can be manipulated by parameters of the additional control field. This feature reflects the idea that applying an additional field to disturb the original dark state may produce double-dark resonances, and that the interaction between the double-dark states can be engineered by the parameters of the additional control field. 

In this article we reviewed some of oiu recent research work related to atomic localization via the effects of atomic coherence and quantum interferences. It was found that the localization property was significantly improved due to the interaction of double-dark resonances. The probability of finding the atom at a particular position could be doubled, as well as the loealization preeision could be dramatically enhanced. A scheme of sub-half-wavelength localization was proposed via two standing-wave fields in a ladder-type system. We also presented an application of atom localization in 2D atom nano-lithograph, through two cavities orthogonal to each other. The feasibility of control the atom localization behaviors by the external optical fields is shown. Those work may be helpful in the experimental research of atom localization. 

D. C. Cheng, Y. P. Niu, and S. Q. Gong. Controllable atom localization via double-dark resonances in a tripod system. Journal of Physics B Atomic Molecular and Optical Physics 2006 Oct 10 23(10) 2180-2184. 

Y. F. Li, J. F. Sun, X. Y. Zhang, and Y. C. Wang. Laser-induced double-dark resonances and double-transparencies in a four-level system. Optics Communications 2002 Feb l 202(l-3) 97-102. 

Figure 4. Level scheme of a lambda-type double-resonance eperiment. The pump laser pulse couples the initial level 1 to a single rovibronic intermediate level 2 in the electronically excited Si state. The intermediate level 2 is coupled by the dump laser pulse to the vibra-tionally excited level 3 in the electronic ground state So- Ionization from level 2 is possible by absorption of an additional photon from the intense dump laser pulse. The coupling of the final level 3 to a single dark state (level 3a) is indicated and discussed in the text.

Compounds that contain allylic and benzylic centres are especially prone to autoxidation, since the radicals formed on oxidation are stabilised by resonance. Oleic acid contains two allylic positions, linoleic acid contains two allylic positions and one double allylic position, while linolenic contains two allylic and two double allylic positions. We would therefore expect linolenic to be the most susceptible acid to oxidation, followed by linoleic and oleic. (The actual relative rates of autoxidation are linolenic (25) > linoleic (12) > oleic (1)). Precautions that can be employed to minimise oxidative deterioration are reducing the oxygen concentration in the container by, for example, the use of an inert atmosphere, and the use of a well-closed and well-filled container. It would also be advisable to store the product at low temperature and in a dark place. 

Most double resonance experiments exploit one of the four energy level schemes shown in Fig. 1.17. The variety of detection schemes is enormous, but most schemes may be divided into those which result in a signal on an essentially dark background vs. those which result in a dip in an essentially constant background level. By definition, the frequency of the PROBE (or DUMP) laser is scanned and that of the PUMP or DETECT laser is held fixed while a double resonance spectrum is being recorded. 

---