Hyperfine Structure-Measurement in Alkali-metal Atoms and Ytterbium Atom
Singh, Alok Kumar
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Atomic precision measurements provide a strong testing ground for new theoretical ideas and fundamental laws of physics. Measurement of the Lamb shift in the hydrogen atom is one of the best examples towards this -it resulted in the birth of QED in 1949 by Dyson, Feynman, Schwinger and Tomonaga. The precision measurements of the hyperﬁne structure in hydrogen and deuterium by Nafe, Nelson and Rabi indicated that the g-factor for the electron was not exactly 2 as predicted by Dirac, but slightly greater, due to QED eﬀects. Thus the precision measurements are indispensable not only for developing new theory but also for the veriﬁcation and ﬁne-tuning of theoretical parameters. Precision measurement of hyperﬁne structure provide valuable information about the nucleus structure, which is helpful in ﬁne tuning of atomic wave-functions used in theoretical calculations. The aim of the work reported in this thesis is the measurement of hyperﬁne frequency and the observation of hyperﬁne structure constant in alkali atoms and in Yb atom. This thesis is organized as follows. In Chapter 1, an introduction to the importance of Alkali atoms and Yb atom in the ﬁeld of precision measurement will be discussed. The scope of this thesis is also discussed in this chapter. In Chapter 2, an introduction to hyperﬁne structure starting from the beginning of the atomic physics will be discussed. We have discussed about the LS-coupling, jj-coupling, and the inﬂuence of the atomic nucleus on atomic spectra. We have also discussed the Zeeman eﬀect and Doppler broadening. In chapter 3, the detail of experimental technique used in this thesis as copropagating satabs, hyperﬁne frequency measurement using AOM scan, AOM lock and ring cavity has been discussed. Experimental technique to observe the EIT signal in two electron Yb system has been discussed, which can be improved the precision in frequency measurement because of the narrow line-width. In chapter 4, we describe the co-propagating saturated-absorption spectroscopy and its application in frequency measurement. Saturated-absorption spectroscopy (satabs) in a vapor cell is a standard technique used to stabilise the laser frequency. In normal satabs we are getting some extra peaks known as a crossover peaks because laser interact with diﬀerent velocity group in a vapor cell. In satabs the crossover peaks are stronger and often swamp the true peaks. So we have developed a technique of co-propagating satabs to remove the spurious peak, which has several advantages over conventional satabs. The co-propagating satabs signal appears on a ﬂat background (Doppler-free) with good signal-to-noise ratio and does not have the problem of crossover resonances in between hyperﬁne transitions. We have adapted this technique to make measurements of hyperﬁne intervals by using one laser along with an acousto-optic modulator (to produce the scanning pump beam). In chapter 5, we describe the measurement of the hyperﬁne interval in the 2P1/2 state of 7Li using the SAS technique in hot Li vapor. This technique produces spurious ground crossover resonances that are more prominent that the real peaks. So we have used this ground crossover to measure the hyperﬁne interval using AOM locking technique. We have developed a technique to measure the absolute frequencies of optical transitions by using an evacuated Rb-stabilized ring-cavity resonator as a transfer cavity. In chapter 6, we study the wavelength-dependent errors due to dispersion at the cavity mirrors by measuring the frequency of the same transition in the Cs D 2 line (at 852 nm) at three cavity lengths. The spread in the values shows that dispersion errors are below 30 kHz, corresponding to a relative precision of 10−10 . We give an explanation for reduced dispersion errors in the ring-cavity geometry by calculating errors due to the lateral shift and the phase shift at the mirrors, and show that they are roughly equal but occur with opposite signs. In chapter 7, we describe precision measurement of hyperﬁne structure in the 3P2 state of 171,173Yb, and see an unambiguous signature of the magnetic octupole coeﬃcient C in 173Yb. The frequencies of the 3P23S1 transition at 770 nm → are measured using a Rb-stabilized ring-cavity resonator with an accuracy of 200 kHz. In 173Yb we obtain the hyperﬁne coeﬃcients as A = − 742.11(2) MHz and B = 1339.2(2) MHz, which represent a two orders-of-magnitude improvement in precision, and C = 0.54(2) MHz. Using atomic-structure calculations for two-electron atoms, we extract the nuclear moments quadrupole Q =2.46(12)b and octupole Ω = 34.4(21)b × µN . The observation of nuclear octupole moment in two-electron atoms, to the best of our knowledge, was never reported before. In 171Yb we obtain the hyperﬁne coeﬃcient A = 2678.49(8) MHz. Using this measurement as well as the previous measurement of A coeﬃcient from our lab, we have compared the hyperﬁne anomalies for 1P1, 3P1 and 3P2 states. In chapter 8, we describe the EIT in two electron system of 174Yb from 1S0(Fg = 0) 3P1(Fe = 1). We have observed the EIT in degenerate two level system and → after lifting the degeneracy by applying the magnetic ﬁeld we are getting ﬁve peaks. We have also observed the EIT in 173Yb. In 173Yb there are three degenerate two level system Fg =5/2 Fe =3/2, Fg =5/2 Fe =5/2, Fg =5/2 Fe =7/2. →→→ We have observed the same type of EIT signal for all the three transitions Fg = FFe = F, ±F + 1. → In Chapter 9, we give a broad conclusion to the work reported in this thesis and suggest future avenues of research to continue the work started here.
- Physics (PHY)