Observation of splitting and optical satellites on the Hδ line of hydrogen due to non-resonant interaction with a CO2 laser radiation
2014 The non-resonant A.C. Stark effects of the na = 6 and 5 manifolds of hydrogen have been studied when excited atoms of a hydrogen glow discharge are irradiated by a T.E.A. CO2 laser beam. Shifts, respectively 0.21 cm-1/MW/cm2 for na = 6, 0.08 cm-1/MW/cm2 for na = 5 are measured, and splitting and optical satellites originating from high orbital quantum numbers are observed on the blue wing of the H03B4 line. Restructuring of this line is described by a perturbative treatment of the interaction. J. Physique LETTRES 42 (1981) L-205 L-209 15 MAI 1981, 1 Classification Physics Abstracts 32.70 32.90 In an early experiment, we succeeded in measuring the shift of the H~ line of hydrogen due to non-resonant perturbation of the na = 6 manifold by a c.w. CO2 laser radiation [1], the so-called light-shift or nonresonant A.C. Stark effect. With laser energy flux IL in the 1-5 MWjcm2 range, the measured shifts (OL6 ~ 1.1 em 1) were in qualitative agreement with theoretical calculations of the A.C. Stark effect developed within the framework of second order perturbation theory [2, 3]. Later on, B. A. Zon [4, 5] reconsidered these calculations taking into account the degeneracy in the orbital moment la, which was neglected in the earlier studies. In particular, B. A~ Zon [4] pointed out that the non-resonant interaction of a laser radiation with an hydrogen state I na, la, ma &#x3E; (ma : magnetic quantum number) leads not only to coupling with other states I nb, lb, mb &#x3E;, (b # a) but also to mixing of the orbital states ~, la, ma ) (la’ ~ la) corresponding to the same principal quantum number na. In this case, the quasi-stationary states for laser fields with polarization vector e are constructed from an expansion of the atomic wave functions (atomic units are used) : , I/Jna(t) is a solution of the time-dependent Schrodinger equation including the interaction operator where d is the atomic dipole moment, }’L and WL are respectively the amplitude and frequency of the laser electric field. A perturbation calculation, valid for V(t) E" a + 1 E" a and for spontaneous and ionization level widths smaller than the detuning from resonance, then leads to the solution : where k, ~~ are respectively the number and the eigen-vectors of the matrix [~] : and Ck are integration constants. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:019810042010020500 L-206 JOURNAL DE PHYSIQUE LETTRES The shift AE~ of quasi-stationary states is related to the eigen-value ~na~ of [~] through the relation : For the case of a linearly polarized field, e = z is the quantization axis, whereas for a right or lefthanded circularly polarized field, e = x ± iy the Yp -,/2quantization axis is clearly defined in the direction of propagation of the radiation. The magnetic sublevels are not then mixed by the field and quantum numbers na, ma well characterize the quasi-stationary states. The following selection rules hold : for linear polarization and ma = ma = mb i!i 1 for right or left-handed polarization. If the field is elliptically polarized (where cos 0 determines the degree of circular polarization of the radiation), there is no axial symmetry (states with ~ 2013 ~ ) I = 2, 4, ... are mixed by the field) and there are no selection rules in mb. Non-resonant interaction with the laser field then leads to a splitting of the hydrogen spectrum which was predicted in the early calculations [2, 3]. Furthermore, a consequence of the formation of new states (P(’) in the laser field is the removal of the orbital momentum selection rules. In particular, for the ~=6-~=2 transition leading to emission of the H~ line, B. A. Zon [5] showed that optical satellites starting from F, G and H sublevels of na = 6 were sufficiently separated from the allowed line and strong enough to be observed with a linearly polarized C02 laser flux IL &#x3E; 1 MW jcm2. In the general case of a partially polarized field, states with different ma are also strongly mixed [6] so that the field completely removes the degeneracy in ma. For these quasistationary states no selection rules hold and they all can decay into a given channel giving rise to additional satellites. Energy of these quasi-stationary states indeed depends on the degree of polarization and varies between the two limiting cases of linearly and circularly polarized fields. Satellites, as well as splitting in the case of level shifts of the same order of magnitude as the Doppler width at room temperature (~ 0.7 cm -1 ), are expected to give rise to broadening and distortion of the blue wing of the shifted Ha line as deduced from the perturbed energy diagram shown in figure 1 and computed from references [2, Fig. 1. Perturbed energy diagram of H8 line computed for IL = 1 MW jcm2 for the linearly polarized C02 laser field. m is the magnetic quantum number and e (even), o (odd) indicate the parity of the sublevels. 3, 5], for IL = 1 MW jcm2 for the linearly polarized CO2 laser radiation (VL = 944 cm-1 ) (1). Such an appearance was in fact observed in reference [1], but the large broadening was attributed to the strong spatial inhomogeneity of the laser beam intensity and to focusing conditions. Similar calculations made for the na = 5 manifold indicate that the Hy line (transition ~=5-~=2) does not show such a broadening but only a mean shift of the whole profile (AE~ ~ 2013 0.07 cm1 when IL = 1 MW/cm2). In this paper, we describe a new experiment in which we study the shifts and the restructuring of the He) and Hy (A,6 = 4 101.7 A) (Ay = 4 340.4 A) lines of the hydrogen atom in nearly uniform laser irradiation conditions and in the IL 10 MWjcm2 range. Comparison between these two different lines allows us to control the experimental conditions and to demonstrate without any doubt the splitting and satellite effects on the laser perturbed Ha line. The experiment is based on measurements of the spectrum of the light emitted by a glow discharge in hydrogen during interaction with a C02 T.E.A. laser beam. In a recent study, we used a low repetition rate (0.05 Hz) T.E.A. CO2 laser constructed in our laboratory and producing 2 J in a 100 ns main pulse to study the non-resonant A.C. Stark effect of the most intense (1) Note that the n’ = 2 level A.C. Stark effect is small enough to be neglected compared to the spin-orbit coupling. This level acts as a detection level of the na = 6 perturbation. L-207 SHIFT, SPLITTING AND SATELLITES OF THE Hð LINE lines of hydrogen (Ha, Hp) and helium (/. = 5 876 A, 5 016 A) [7]. The GEN-TEC DD 250 T.E.A. C02 laser available in the present experiment produces 600 mJ in a 150 ns main pulse at À = 10.59 ~m. Working at a repetition rate of 10 Hz, with shot-to-shot variation of the laser power within 10 % and jitter restricted to 10 ns, accumulation techniques have been developed to enhance S/N ratio and detectivity of weak lines. The experimental set-up is shown in figure 2. Excited states are populated in a capillary glow discharge (inner diameter 4 mm, length 20 mm). The discharge is created in high purity hydrogen gas by current pulses (intensity : 1-5 A, width = 80 ~s) superimposed on a weak D.C. current (i ~ 10 mA). Fig. 2. Experimental set-up : 1) discharge power supply; 2) T.E.A. C02 laser; 3) Monochromator; 4) Monitoring system and gated integrators; 5) Recorder; 6) I.R. Monochromator; 7) P.M. power supply. Pressure can be adjusted from 0.1 to 10 torr. Characteristics of the ionized gas have been determined elsewhere [8] : electronic density ne 5 x 1012 cm3, mean electronic energy ~ 3-8 eV, gas temperature ~ 340 K. The partially polarized CO2 laser beam is partially focused along the discharge tube in order that the whole volume inside the capillary tube is irradiated. In the present experiment, the mean laser intensity IL in the central part of the tube is limited to 6 ± 1 MW/cm2 and is measured at the output of the discharge tube taking into account transmission of the NaCI window. Observation of the laser intensity at the output of the discharge tube indicates a near uniform distribution in the central part (diameter ~ 2 mm) viewed by the spectrometer. The fluorescence light emitted by the discharge is observed axially and is imaged onto the slit of a 1.15 m S.O.P.R.A. motor-driven grating spectrometer and then onto a R.C.A. 7265 photomultiplier tube. Slit widths are adjusted in order to give a resolution of 0.12 A in the vicinity of À = 4 101.7 A. The line shapes are scanned at speeds as low as 0.08 A/min. The whole system is synchronized by a clock which lights the discharge at 20 Hz and triggers the laser at 10 Hz. A two channel (A and B) gated integrator synchronized by this clock analyses the photomultiplier signal. The number of shots accumulated by the two integrators, as well as processing of the output signal are controlled by a M6800 microprocessor evaluation board. Gate A, 100 ns wide, is temporally positioned about the peak of the laser pulse, the discharge being on. Alternately, gate B, similar to A, is opened only when discharge is on and laser off. Thus, for a given wavelength ~, and a predetermined number of shots, one gets alternately at a rate of 10 Hz, the intensity J(~,) of the laser perturbed line in A and the intensity J’(~,) of the same but unperturbed line in B. The outputs of gates A and B are displayed on a two channel strip chart recorder. The perturbed and unperturbed line profiles are obtained simultaneously by slowly rotating the grating of the spectrometer. Each point on the profile corresponds to a summation over 100 or 200 shots, that is an accumulation time of 10 (20) s and a scanned spectral range of 0.013 (0.026) A which is small enough to ensure no resolution loss. Observations of the laser pulse shape indicate that during the 100 ns duration of a single measurement, I L(t) varies typically between 75 and 100 % of its peak value. This leads to a corresponding variation of the A.C. Stark shift which finally app
A two-step process in the 210Pb(p, d)209Pb reaction
Abstract The 210 Pb(p, d) 209 Pb reaction leading to the single particle states of 209 Pb have been analyzed. In the weak transitions to the li 11/2 , 3d 5/2 , 4s 1/2 , 2g 7/2 and 3d 3/2 single particle states the contribution of the two-step process p→t→d was found to be of the same order of magnitude as the direct pick-up process. The calculated cross sections taking both the direct pick-up and the two-step processes into account agree well with the experimental ones. Two step processes via inelastic scattering were found to be small.
Monte Carlo simulations of magnetovolume instabilities in anti-Invar systems
We perform constant pressure Monte Carlo simulations of a spin-analogous model which describes coupled spatial and magnetic degrees of freedom on an fcc lattice. Our calculations qualitatively reproduce magnetovolume effects observed in some rare earth manganese compounds, especially in the anti-Invar material YMn2. These are a sudden collapse of the magnetic moment which is connected with a huge volume change, and a largely enhanced thermal expansion coefficient.