Cesium D Line Data - Steck

1 Cesium D line DataDaniel A. SteckTheoretical Division (T-8), MS B285 Los Alamos National LaboratoryLos Alamos, NM 8754523 January 1998(revision , 14 October 2003)1 IntroductionIn this reference we present many of the physical and optical properties of Cesium that are relevant to variousquantum optics experiments. In particular, we give parameters that are useful in treating the mechanical effects oflight on Cesium atoms. The measured numbers are given with their original references, and the calculated numbersare presented with an overview of their calculation along with references to more comprehensive discussions oftheir underlying theory. We also present a detailed discussion of the calculation of fluorescence scattering rates,because this topic is often not treated carefully in the current version of this document is available , along with Sodium DLine data and Rubidium 87 D line data .

2 Please send comments and corrections Cesium Physical and Optical PropertiesSome useful fundamental physical constants are given in Table 1. The values given are the 1998 CODATA recommended values, as listed in [1]. Some of the overall physical properties of Cesium are given in Table has 55 electrons, only one of which is in the outermost is the only stable isotope of Cesium ,and is the only isotope we consider in this reference. The mass is taken from the high-precision measurementof [2], and the density, melting point, boiling point, and heat capacities are taken from [3]. The vapor pressure at25 C and the vapor pressure curve in Fig. 1 are taken from the vapor-pressure model given by [4], which islog10Pv= 00 + 361 85T+ 52 log10T(solid phase)log10Pv= 27 601 94T 23 log10T(liquid phase),(1)wherePvis the vapor pressure in torr, andTis the temperature in K.

3 This model should be viewed as a roughguide rather than a source of precise vapor-pressure values. The ionization limit is the minimum energy requiredto ionize a Cesium atom; this value is taken from Ref. [5] (another measurement of 31 (7) cm 1[6] is notincluded due to substantial disagreement with the more recent value quoted here).The optical properties of the Cesium D line are given in Tables 3 and 4. The properties are given separately foreach of the two D- line components; the D2line (the 62S1/2 62P3/2transition) properties are given in Table 3,and the optical properties of the D1line (the 62S1/2 62P1/2transition) are given in Table 4. Of these twocomponents, the D2transition is of much more relevance to current quantum and atom optics experiments, becauseit has a cycling transition that is used for cooling and trapping Cesium .

4 The frequencies 0of the transitions were2 Cesium PHYSICAL AND OPTICAL PROPERTIES2measured using an optical frequency comb [7, 8]; the vacuum wavelengths and the wave numberskLare thendetermined via the following relations: =2 c 0kL=2 .(2)The air wavelength air= /nassumes index of refraction ofn= 268 21, corresponding to dry air at apressure of 760 torr and a temperature of 22 C. The index of refraction is calculated from the Edl en formula [9]:nair=1+ +2 406 030130 2+15 2 388 23P1+ 671T f 2 10 8.(3)Here,Pis the air pressure in torr,Tis the temperature in C, is the vacuum wave numberkL/2 in m 1,andfis the partial pressure of water vapor in the air, in torr. This formula is appropriate for laboratory conditionsand has an estimated uncertainty of 10 lifetimes are averaged from recent measurements; the first [10] used a fast beam laser technique, yieldinglifetimes of (10) ns for the 62P1/2state and (7) ns for the 62P3/2state, while the second [11] used aphoton-counting method, giving lifetimes of (7) ns (62P1/2) (10) ns (62P3/2) state.

5 The formermeasurement is taken to supersede several measurements by some of the same experimenters using the sametechnique [12, 13], and another measurement of comparable quoted uncertainty ( (2) ns for the 62P3/2state)[14] is excluded because of a substantial disagreement with all recent precision measurements [10]. Anotherprecise measurement of the ratios of the D1and D2transition strengths [15] of| J=1/2 er J =3/2 |2/| J=1/2 er J =1/2 |2= (9) was factored into the weighted averages quoted here. A general discussion ofprecision lifetime measurement methods can be found in [16]. Inverting the lifetime gives the spontaneous decayrate (EinsteinAcoefficient), which is also the natural (homogenous) line width (as an angular frequency) of theemitted spontaneous emission rate is a measure of the relative intensity of a spectral line .

6 Commonly, the relativeintensity is reported as an absorption oscillator strengthf, which is related to the decay rate by [17] =e2 202 0mec32J+12J +1f(4)for aJ J fine-structure transition, wheremeis the electron recoil velocityvris the change in the Cesium atomic velocity when absorbing or emitting a resonant photon,and is given byvr= hkLm.(5)The recoil energy h ris defined as the kinetic energy of an atom moving with velocityv=vr,whichis h r= h2k2L2m.(6)The Doppler shift of an incident light field of frequency Ldue to motion of the atom is d=vatomc L(7)for small atomic velocities relative toc. For an atomic velocityvatom=vr, the Doppler shift is simply 2 r. Finally,if one wishes to create a standing wave that is moving with respect to the lab frame, the two traveling-wavecomponents must have a frequency difference determined by the relationvsw= sw2 2,(8)because sw/2 is the beat frequency of the two waves, and /2 is the spatial periodicity of the standing a standing wave velocity ofvr,Eq.

7 (8)gives sw=4 r. Two temperatures that are useful in cooling and3 HYPERFINE STRUCTURE3trapping experiments are also given here. The recoil temperature is the temperature corresponding to an ensemblewith a one-dimensional rms momentum of one photon recoil hkL:Tr= h2k2 LmkB.(9)The Doppler temperature,TD= h 2kB,(10)is the lowest temperature to which one expects to be able to cool two-level atoms in optical molasses, due to abalance of Doppler cooling and recoil heating [18]. Of course, in Zeeman-degenerate atoms, sub-Doppler coolingmechanisms permit temperatures substantially below this limit [19].3 Hyperfine Energy Level SplittingsThe 62S1/2 62P3/2and 62S1/2 62P1/2transitions are the components of a fine-structure doublet, and eachof these transitions additionally have hyperfine structure.

8 The fine structure is a result of the coupling between theorbital angular momentumLof the outer electron and its spin angular momentumS. The total electron angularmomentum is then given byJ=L+S,(11)and the corresponding quantum numberJmust lie in the range|L S| J L+S.(12)(Here we use the convention that the magnitude ofJis J(J+1) h, and the eigenvalue ofJzismJ h.) For theground state in Cesium ,L=0andS=1/2, soJ=1/2; for the first excited state,L=1,soJ=1/2orJ=3 energy of any particular level is shifted according to the value ofJ,sotheL=0 L= 1 (D line ) transitionis split into two components, the D1line (62S1/2 62P1/2)andtheD2line (62S1/2 62P3/2). The meaningof the energy level labels is as follows: the first number is the principal quantum number of the outer electron, thesuperscript is 2S+ 1, the letter refers toL( , S L=0,P L= 1, etc.)

9 , and the subscript gives the hyperfine structure is a result of the coupling ofJwith the total nuclear angular momentumI. The totalatomic angular momentumFis then given byF=J+I.(13)As before, the magnitude ofFcan take the values|J I| F J+I.(14)For the Cesium ground state,J=1/2andI=7/2, soF=3orF= 4. For the excited state of the D2line(62P3/2),Fcan take any of the values 2, 3, 4, or 5, and for the D1excited state (62P1/2),Fis either 3 or 4. Again,the atomic energy levels are shifted according to the value the fine structure splitting in Cesium is large enough to be resolved by many lasers ( 42 nm), thetwo D- line components are generally treated separately. The hyperfine splittings, however, are much smaller, andit is useful to have some formalism to describe the energy shifts.

10 The Hamiltonian that describes the hyperfinestructure for each of the D- line components is [17, 20]Hhfs=AhfsI J+Bhfs3(I J)2+32I J I(I+1)J(J+1)2I(2I 1)J(2J 1),(15)3 HYPERFINE STRUCTURE4which leads to a hyperfine energy shift of Ehfs=12 AhfsK+Bhfs32K(K+1) 2I(I+1)J(J+1)2I(2I 1)2J(2J 1),(16)whereK=F(F+1) I(I+1) J(J+1),(17)Ahfsis the magnetic dipole constant, andBhfsis the electric quadrupole constant (although the term withBhfsapplies only to the excited manifold of the D2transition and not to the levels withJ=1/2). These constants forthe Cesium D line are listed in Table 5. The constants listed for the 62P3/2manifold were taken from a more recentand precise measurement by Tanner and Wieman [21]. TheAhfsconstant for the 62P1/2manifold is a weightedaverage of a frequency-comb measurement (Ahfs= (20) MHz) [8] and a crossed-beam laser spectroscopymeasurement (Ahfs= (8) MHz) [22].