The effects of degeneracy on self-induced transparency (SIT) have been studied using optical pulses gated from a cw dye laser and four different degenerate systems in Na. , Delays, nonlinear transmission, peaking, and breakup were altered only slightly by degeneracy. This unexpected insensitivity to degeneracy of SIT features is in agreement with the McCall-Hahn pulse-area, pulse-energy description, computer simulations, and a simple physical explanation of general applicability.Degeneracy has been assumed to prevent the observation of such characteristic features of self-induced transparency (SIT) as peak amplification and breakup of an optical pulse. 1 " 3 We report an experiment which clearly demonstrates that degenerate transitions do not prevent the observation of all of the characteristic features of SIT.SIT was first demonstrated in ruby 4 and immediately afterwards in SF 6 . 5 The complicated energy-level structure of SF 6 led to interest in the effects of degeneracy, but it was assumed that degeneracy prevented peaking and pulse breakup. 1 " 3 The effects of degeneracy on SIT phenomena are clarified here in sodium vapor using a dye laser. There are three advantages of this system over the CO z laser-SF 6 system. First, sodium (Na) is a simpler system with clearly defined degenerate transitions with known dipole moments. Second, for weak magnetic fields there are at least two sets of clearly defined combinations of moments which can be studied independently. Third, in high magnetic fields the Na system becomes nondegenerate. Therefore, the same system can be used to study both nondegenerate and degenerate SIT.The basic apparatus consisted of a cw dye laer 6 and Na absorption cell. The spectral profile of the dye laser was reduced from about 0.5 A to 20 MHz in a single longitudinal mode by the use of three etalons. The output of the dye laser was then gated through a Glan prism by a Pockels cell at the rate of 100 pulses per second. 7 This resulted in 5-nsec pulses which were focused by a 38-cm lens into a 2-mm sodium cell. The sodium cell was housed in an oven and placed in a magnetic field which could be varied from 0 to 8 kG. A 15-cm lens was used to image the excited region in the cell onto a 100-jnm aperture in order to select only the uniform-plane-wave region for observation. 7 The output from the aperture was then focused by a third lens onto a fast detector and then displayed on a 7904 Tektronix oscilloscope. 7 A quantitative study of peak amplification and breakup was carried out by Gibbs and Slusher, using a Hg laser and Rb atoms. 7 Because they found such good agreement between theory and experiment, it is desirable to start with a similar nondegenerate system and then observe what happens when degeneracy is added. In large magnetic fields Na transitions of different Mj are well resolved, but several M 7 transitions are excited as a result of a large Doppler width. However, the system is effectively nondegenerate since the moments are all equal. As shown in Fig. 1, the dye-laser-Na data taken i...
Charge transfer and ionization, producing high concentrations of doubly ionized ions, is identified for the first time in analytical GD-MS.
The 2 Pf/2 ground state of thallium has been optically pumped in the presence of various buffer gases. The measured cross sections for the destruction of the electron polarization are small (10~1 9 to 10" 17 cm 2 ), verifying the selection rule Mjf* -Mj for the adiabatic contributions and demonstrating the strong dependence of the nonadiabatic contributions upon the multiplet energy separation.The 2 P ± / 2 ground state of Tl has been optically pumped. The electron randomization cross sections have been measured to be (at 610°C, in units of 10~2 0 cm 2 , and with a ±30% uncertainty) He, 60; Ne, 14; Ar, 110; Kr, 220; Xe, 620; H 2 , 380; N 2 , 920. Diffusion coefficients of Tl have been measured to be (in units of cm 2 /sec at 510°C, at atmospheric pressure, and with a 50% uncertainty) He, 1.7; Ne, 0.79; Ar, 0.35. The cross sections are the smallest yet found for a state with nonzero orbital angular momentum.In 1966 it was suggested that collisional relaxation might be diminished within the Zeeman sublevels of an energetically isolated 2 P 1 / 2 state. 1 This was verified in Rb and Cs, where the cross sections (a's) were found to be 10 to 50 times smaller than geometric a's. 2 A selection rule M j-f-Mj was derived by assuming an odd total number of electrons, a time-reversal-invariant interaction Hamiltonian, a large energy separation AE between the 2 P x / 2 and 2 P 3 / 2 states, and the neglect of nonadiabatic terms. 2 " 4 Since the rule Mj-fi -Mj depends strongly on AE (238 cm*" 1 in Rb; 554 in Cs; 7793 in Tl), the 2 P l/2 relaxation should be much weaker in Tl than in Rb and Cs. But the failure of several laboratories to optically pump Tl (and reported 5 theoretical and preliminary experimental a's for Cs larger than Gallagher's) weakened Gallagher's experimental demonstration 2 of the rule Mj^-Mj.However, the successful optical pumping of Tl and the smallness of the a's reported here establish the rule Mj / -Mj in the Tl ground state.Natural Tl consists of Tl 203 and Tl 205 , each with nuclear spin f. An atom in a given sublevel F,M of the 2 P 1 / 2 state cannot make a transition to another sublevel F,M' without violating either Mj -f -Mj or AMj = 0; such is not the case in the 2 P 3 / 2 state. Small a's in the 2 P 1 / 2 state therefore imply that both the selection rules AM x = 0 and Mj-f-Mj are operative. Nuclear spin complicates the analysis by introducing three resolved hyperfine components. 6 Let L FF * be proportional to the incident light intensity absorbable in a transition from the F hyperfine level of the 2 P x / 2 state to the F' level of the 2 S l/2 excited state. The absorption of circularly polarized light incident along the magnetic field is A cp = L 01 n 00 + L 10 n 1 ^^L^^ -!+%>), where n FM is the density of the M sublevel of the F level. If all hyperfine components are equal (L FF ,=L), then A cp = Lin-in^-fi! " 1 )] = Ln(l-2(J g » 9 where n = n 11 +n 10 +n 1 ~x + n 00y and (J g ) is the electronic polarization. The collisional relaxation of 263
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