Hyperfine structure and isotope shift of the 640.2 and 626.6 nm lines of neon

2014 A tunable single mode laser has been used to excite the 03BB = 640.2 and 626.6 nm lines of 20Ne, 21Ne and 22Ne. Using the velocity selective optical pumping method, we have measured the hyperfine structures and isotopic shifts of these two lines. We obtain the following values for the 21Ne hyperfine structure constants of the 2p9 level : We have also measured isotope shifts and obtained values in good agreement with the mass-shift formula. J. Physique LETTRES 41 (1980) L-479 L-482 Classification Physics Abstracts 32.20J 32.80B 35.208 15 OCTOBRE 1980, The hyperfine structure constants A and B of the levels belonging to the 2ps3p electronic configuration of 21Ne (I = 3/2) have been measured by various experimental techniques. Giacobino [1] used the levelcrossing method to obtain A and B for the 2P2, 2p4, 2ps, 2P6, 2p7 and 2p8 levels, and Husson and Grandin [2] for the 2PI0 level. An absorption line narrowing method was used by Delsart and Keller [3] to measure the 2p4 hyperfine constants. Nevertheless, the hyperfine structure of the 2p9 level has not yet been experimentally measured, presumably because this level has a J = 3 value and is radiatively connected only to one lower level, the Iss (3P2) level. This situation can raise experimental problems in level-crossing experiments, since it is often convenient to detect the atomic fluorescence at a wavelength which differs from that used for excitation. These difficulties do not occur with absorption techniques, such as the Doppler-free velocity selective optical pumping spectroscopic method [4]. We thus decided to use this method in order to measure hyperfine structure constants of 21 Ne. 1. Experimental set-up. The experimental set-up is very similar to the description given in reference [4]. The neon gas was contained in sealed pyrex cells, 6 cm in diameter, with some helium buffer gas (p = 50 mtorr); the metastable levels of Ne were populated by an electrodeless discharge (v 12 MHz). Two different cells were used : one containing a partial pressure p = 12 mtorr of 21Ne, the other 5 mtorr of natural neon (90 % of 2°Ne, 10 % of 22Ne). The pumping beam was provided by a single mode cw dye laser, operating with a double Michelson mode selector, and placed inside an air-tight box for pressure scanning of the frequency [5]. The frequency of the laser was locked on an external plane Perot-Fabry cavity (5 cm quartz spacers), inside a second box, which was independently pressure scanned. The low frequency part of the error signal was used to drive the pressure of the laser box, the high frequency part to act on a PZT ceramics and to change the dye laser cavity length (this operation reduced the frequency jitter to about 4 MHz). A mixture of two dyes, R6G and R640, was used to obtain both wavelengths, Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:019800041020047900 L-480 JOURNAL DE PHYSIQUE LETTRES A = 6 266 and 6 402 A. The pumping beam was expanded to about 1 cm2 in order to avoid any saturation of the optical transition. Large velocity selective optical pumping signals were obtained with hyperfine pumping inside the lower electronic level (this pumping occurs with any pump polarization). This is why the linear polarization of the dye laser was directly used in most experiments. Nevertheless, in a few cases (2°Ne-22Ne isotope shift for example), better signals were obtained, like in [4], with a circular pump polarization which allows one to create an atomic orientation. The counterpropagating beam was provided by the same laser; the use of a beam splitter made unnecessary any angle between the pump and beam. The pump beam intensity was modulated at 40 kHz ; this frequency is high enough to correspond to a low laser intensity noise, and to reduce considerably the collision-induced background of the spectra [6] (this background arises mainly from Ne-He collisions which transfer hyperfine population differences between distinct velocity classes). Then, only atoms that are simultaneously in resonance with both laser beams contribute to the signal. 2. Structure of the spectra. When the laser frequency is swept over an atomic resonance line, different kinds of narrow (Doppler-free) resonances are observed. Let us for example discuss the line structure which occurs when the ~= 6 402 A line (J= 2 ~ J= 3) of 21 Ne is used. The pumping process does not affect the total population of the 3p 2 state (as far as collisional transfer does not reduce the excited state population). In other words, the sum of the four hyperfine populations F = 1/2, 3/2, 5/2 and 7/2 of the 3P2 metastable state is constant, and the optical pumping regime ensures that the hyperfine populations F’ = 3/2, 5/2, 7/2 and 9/2 of the excited state are negligible. So, the signals observed are mainly due to hyperfine pumping inside the 3P2 state (with a linear laser polarization, the alignment of each F level can also contribute to the signal). Two kinds of resonances appear : direct resonances corresponding to atoms with a zero velocity component along the beam, and cross-over resonances corresponding to non-zero velocities. The positions of the former give directly atomic transition frequencies, while the positions of the latter correspond to the half sum of two atomic frequencies. More specifically, we can expect the following reso-