CHƯƠng trình hội nghị VÀ TÓm tắt báo cáO

Dinh Xuan Khoa(1), Le Canh Trung(1), Le Thi Minh Phuong(2), and Nguyen Huy Bang (1)

The alkali-metal diatomic molecules with their main absorption bands in the UV-VIS region are very convenient for modern laser spectroscopy techniques. Experimental investigations for these molecules have further promoted since the emergence of molecular Bose-Einstein condensates (see [1] and references therein). As several experimental techniques related to cold molecules involve optical excitation either in the formation or detection stages, an accurate need of precise spectroscopic characterization of excited molecular states has arisen.

Among alkali-metal diatomic molecules, NaLi is particularly interested because it is the lightest hetero-nuclear type and has permanent dipole moment, thus can be manipulated with external electric fields. Several experimental investigations for NaLi were performed to study up to the 71Π excited states [2-7]. Although the 21 state was investigated [4] but its rotational characterization was not described due to low resolution of experimental data.

In this work, we determinate molecular constants for the 21Π state of NaLi from set of 732 spectral lines [8]. Using the linear least-squares fitting method, an optimum set of molecular constants, which corresponds to dimensionless root mean of squares of deviation = 0.62 within 0.1 cm-1 experimental uncertainty, have been derived.

References

[1] S. Jochim et al., Science 302 (2003) 2101.

[2] C.E. Fellows, J. Chem. Phys., 94 (1991) 5855; J. Mol. Spectrosc, 136 (1989) 369.

[3] C.E. Fellows, J.Vergès, and C. Amiot, J. Chem. Phys., 93  (1990) 6281-6290.

[4] M. M. Kappe, K. O. Marti, P. Radi, M. Schäp, and E. Scgumacher, Chem. Phys. Lett.,107 (1984) 6.

[5]. W. Jastrzębski, P. Kowalczyk, R. Nadyak, and A. Pashov, Spectrochim. Acta, Part A, 58A (2002) 2193.

[6] I. D. Petsalakis et al., Chem. Phys., 362 (1999) 130.

[7] Nguyen Huy Bang et. al. J. Mol. Spectr. 233 (2005) 290; Optica. Applicata. 36 No4 (2006) 499; Chem. Phys. Lett. 440 (2007) 199; Opt. Mat. 31(2009) 527; J. Chem. Phys. 130 (2009) 124307.

[8] Le Canh Trung et al. “First rotational spectroscopic observation of the 21П state of NaLi”, paper at this Conference.

Nguyen Tien Dung, Le Canh Trung, Nguyen Van Thinh, Hoang Cong Vieng, Le Hong Quang, Phan Van Thuan, Vu Ngoc Sau, Doan Hoai Son, Dinh Xuan Khoa, and Nguyen Huy Bang

The advent of femto-second laser spectroscopy techniques opens ways to explore dynamical processes in molecules after optical excitations. The molecular dynamics has been now an interesting field for spectroscopists, biologists, and chemists in order to understand intermolecular/intramolecular transitions. As in experiments concerning to molecular dynamics, the population distribution of vibrational levels in the excited electronic states is crucial information for setting parameters [1]. Recently, alkali-metal diatomic molecules are particular interested for this kind of spectroscopic experiment because of their simple electronic structure and their spectra lying in UV-VIS region, which is easily excited by commercial laser sources. Therefore, knowing of vibrational population characterization for this kind of molecules is needed.

In this work, we calculate population density of vibrational levels up to the near dissociate limit of the 21 of NaLi by using Numerov-Cooley method [2]. The confidence of calculation is tested by comparing Franck-Condon factors to the experimental spectra of 2111+ band system [3].

References

[2] J. W. Cooley. An Improved eigenvalues Corrector Formula for solving the Schrödinger Equation for Central Fields. Math. Comput. XV (1961) 363.

[3] Le Canh Trung et al. “First rotational spectroscopic observation of the 21П state of NaLi”, paper at this Conference

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.