HỘi nghị VẬt lý LÝ thuyết toàn quốc lần thứ 37 The 37th National Conference on Theoretical Physics

Nguyen Tien Dung(1), Le Canh Trung(1), Chu Manh Hoai(2), Dinh Xuan Khoa(1), and Nguyen Huy Bang(1)

Knowing of potential energy curves (PEC) of diatomic molecules plays important role in atomic and molecular physics because it can provide information for prediction of atomic colissions, chemical bondings, and dispersion forces. Construction of PECs from experimental data therefore attracts great attention of spectroscopists. There are revelral ways to archieve this goal. Perhaps the simplest one is to fit the data to the simple Morse function in which only two adjustable parameters to be determined. More adjustable parameters can be introduced to get more flexible form of PEC, but however for modern accurate spectroscopic measurements such models are not sufficient enough for interpretation of overal data. Up-to-date, twoo methods for construction of a PEC which is satisfy a given accurate demand. The first one is the Inverted Perturbation Approach (IPA) which was proposed by Kosman et al [1] and Vidal et al [2] and then developed by Pashov et al [3]. The second method is to fit directly spectroscopic data to analytical potential model, known as DPOTFIT, which was proposed by R.Leroy [4]. Though both methods are fully quantum mechanical but requirement in application is somehow different.

In this paper we present construction of PEC for the 31П of NaLi molecule by means of IPA and DPOTFIT methods. Here, the previous PEC which was determined numerically by the semi-classical Rydberg-Klein-Rees method reported in the previous work [5] is employed as a trial. Some important aspects concerning to the constructed potential are discussed.

References

[1] W. Kosman et al., J. Mol. Spectrosc. 56 (1975) 93.

[2] C. Vidal et al., J. Mol. Spectrosc. 65 (1977) 46.

[3] A. Pashov et al., Comput. Phys. Commun 128 (2000) 622.

[4] R. Leroy, in: Molecular Spectroscopy, Vol 1, Eds. R. F. Barrow, D. A. Long, and D. J. Millen (Chem. Soc., London, 1973).

[5] Nguyen Huy Bang et al., Chem. Phys. Lett, 440 (2007) 199.

Le Van Doai(1), Pham Van Trong(2), Dinh Xuan Khoa(1), and Nguyen Huy Bang(1)

Recently, we have witnessed a growing interest on the creating nonlinear optical material of large Kerr nonlinear index of refraction since it can be used for many interesting applications, such as cross-phase modulation for optical shutters [1], self-phase modulation for generating optical solitons [2], four-wave mixing processes for frequency conversion [3], entangled states for quantum information processing [4], and low light-level optical bistable devices [5]. In conventional Kerr material, its nonlinear index is so small so that the nonlinear effect is significant for strong light intensity, thus for short pulses. The advent of electromagnetically induced transparency (EIT) [6] has opened a promising way to enhance significantly Kerr nonlinearity of atoms around resonant frequency without absorption. Several works concentrated to the three-level atomic systems (see [7] and ref. therein) in which an intense laser light induces atoms to create an EIT window corresponding to a narrow region of giant Kerr index.

Extension of spectral region of EIT enhanced Kerr nonlinearity in atoms is straightforward to realized applications. In order to attain this goal, we propose to use a five-level cascade scheme in Rb85 induced by a light strong coupling laser under EIT condition. Using perturbation theory we derive an expression of the nonlinear Kerr index in an analytical form. Influence of parameters of coupling field, namely, frequency detuning and intensity, on the Kerr index is discussed.

3. References

[2] Tikhonenko, V., Christou, J., and Luther-Davies, B., 1996, Phys. Rev. Lett., 76, 2698.

[3] M. Jain, H. Xia, G.Y. Yin, A. J. Merriam, and S.H. Harris, Phys. Rev. Lett. 77, 4326 (1996).

[4] S. E. Harris and Y. Yamamoto, Phys. Rev. Lett. 81, 3611(1998).

[5] G. S. He and S. H. Liu: Physics of Nonlinear Optics, World Scientific 2002.

[6] K. L. Boller, A. Imamoglu, and S. E. Harris, Phys. Rev.Lett. 66, 2593 (1991); J. E. Field, K. H. Hahn, and S. E.Harris, Phys. Rev. Lett. 67, 3062 (1991).

[7] M. Fleischhauer, A. Imamoglu, J. P. Marangos, Rev.Mod.Phys.,77 (2005) 633-673..

Le Van Doai(1), Bui Hong Hai(1), Trinh Thi Hong(1), Pham Van Trong(2), Phan Van Dao(3), Tran Manh Cuong(1), Mai Van Luu(1), Vu Ngoc Sau, Doan Hoai Son(1), Dinh Xuan Khoa(1), and Nguyen Huy Bang(1)

Recently, we have witnessed a growing interest on the creating nonlinear optical material of large Kerr nonlinear index of refraction since it can be used for many interesting applications, such as cross-phase modulation for optical shutters [1], self-phase modulation for generating optical solitons [2], four-wave mixing processes for frequency conversion [3], entangled states for quantum information processing [4], and low light-level optical bistable devices [5]. In conventional Kerr material, its nonlinear index is so small so that the nonlinear effect is significant for strong light intensity, thus for short pulses. The advent of electromagnetically induced transparency (EIT) [6] has opened a promising way to enhance significantly Kerr nonlinearity of atoms around resonant frequency without absorption. Several works concentrated to the three-level atomic systems (see [7] and ref. therein) in which an intense laser light induces atoms to create an EIT window corresponding to a narrow region of giant Kerr index. Extension of spectral region of EIT enhanced Kerr nonlinearity in atoms is straightforward to realized applications. In order to attain this goal, we propose to use a four-level lambda scheme in Rb^85 induced by a light strong coupling laser under EIT condition. Using perturbation theory we derive an expression of the nonlinear Kerr index in an analytical form. Influence of parameters of coupling field, namely, frequency detuning and intensity, on the Kerr index is discussed. References [1] Schmidt, H., and Imamoglu, A., 1996, Opt. Lett., 21, 1936 [2] Tikhonenko, V., Christou, J., and Luther-Davies, B., 1996, Phys. Rev. Lett., 76, 2698. [3] M. Jain, H. Xia, G.Y. Yin, A. J. Merriam, and S.H. Harris, Phys. Rev. Lett. 77, 4326 (1996). [4] S. E. Harris and Y. Yamamoto, Phys. Rev. Lett. 81, 3611(1998). [5] G. S. He and S. H. Liu: Physics of Nonlinear Optics, World Scientific 2002. [6] K. L. Boller, A. Imamoglu, and S. E. Harris, Phys. Rev.Lett. 66, 2593 (1991); J. E. Field, K. H. Hahn, and S. E.Harris, Phys. Rev. Lett. 67, 3062 (1991). [7] M. Fleischhauer, A. Imamoglu, J. P. Marangos, Rev.Mod.Phys.,77 (2005) 633-673.

K. Doan Quoc, V. Cao Long, W. Leoński

In our previous paper [1], electromagnetically induced transparency (EIT) for -like systems introduced in [2] has been considered, where the laser coupling light applied in the model is assumed to be a -correlated, Gaussian, Markov, stationary process (white noise) [3]. We now investigate a similar scheme, where the continuum involved in the problem is replaced by one with so-called double Fano structure [4]. We derive a set of coupled stochastic integro-differential equations which can be averaged exactly. This leads to the exact formula determining the stationary solution for the electric susceptibility. Dispersion and absorption spectra for EIT are found and compared with those obtained previously in [1,2,4]. References [1] K. Doan Quoc, V. Cao Long, W. Leoński, Phys. Scr. T147 (2012) 014008. [2] A. Raczyński, M. Rzepecka, J. Zaremba and S. Zielińska-Kaniasty, Opt.Commun. 266, 552 (2006). [3] V. Cao Long and M. Trippenbach, Z. Phys. B – Condensed Matter 63, 267 (1986). [4] W. Leoński, R. Tanaś and S. Kielich, J. Opt. Am. B4, 72 (1987).

M.T.Nguyen(1), T.V.Koval(1), A.G.Zherlitsyn(2), G.G.Kanaev(2)

The results of experimental and theoretical investigations of microwave radiation excitation in coaxial vircator with a radially symmetric divergent beam are presented in the paper. The influence of system geometry and beam parameters on the formation of virtual cathode and emission characteristics has been conducted. Theoretical studies have been carried out using numerical simulation program based on particle-in-cell method. The dependence of current, frequency characteristics and radiation power on geometry and beam parameters has been obtained experimentally and numerically. In the experiment, using an input voltage pulse with peak value of 550 kV the average voltage obtained on the diode is 450 kA and the diode current is 50 kA, the peak value of output microwave power of coaxial vircator is observed to be over 300 MW in frequency band 2.95-3.1 GHz.