The commonly quoted saturation intensity of rubidium (Rb) for D2 transitions is 16.7
W.m−2. This value, however, is only accurate for the cycling transition, which renders the Rb atom to resemble a two-level system. In practice, the effective saturation intensity is influenced by various factors, such as the polarization of light, optical pumping, and atom collision which can redistribute the population. As a result, it is crucial to experimentally determine the effective saturation intensity. In this context, we demonstrate a novel yet simple experimental method to measure the effective saturation intensities of Doppler-broadened transitions in atomic vapours. Our method only requires on-resonance absorbance data for various input laser intensities, which can be obtained with a tunable CW laser without the need for precise frequency locking. We applied this method to measure the effective saturation intensities of all four Doppler-broadened D2 transitions in natural rubidium (Rb) vapour (27.8%87Rb and 72.2 %
85Rb) at
r=35∘C. The results show that the effective saturation intensities for Rb range from 0.752 to 16.8
W.m−2. Notably, for certain transitions (specifically, repump transitions), the effective saturation intensities were smaller than 16.7 W.
m−2(up to an order of magnitude), with potentially important implications for optical pumping in Doppler-broadened transitions.
Summary form only given. We have studied the absorption and fluorescence of the D/sub 2/ line [6S/sub 1/2/(F=3,4)-6P/sub 3/2/(F=2,3,4.5)] in dilute Cs atomic vapour for 3 vapour cells: an extremely thin cell with a column length of 8 /spl mu/m, a 16.5 mm-long cell with pure Cs vapour, and a 10.4 mm-long Cs cell containing 40 Torr of Ne. A laser diode with a 20 MHz-linewidth and the maximum intensity of 40 mW/cm/sup 2/ was used. In order to have a comparable peak absorption (for the case of low laser intensity), the extremely thin cell was heated to /spl sim/100/spl deg/C. The effective absorption cross-sections of these cells versus laser intensity are shown. It is important to note that the same behaviour was observed for the resonance fluorescence. The effect of optical pumping of Zeeman sublevels, leads to a dramatically different behaviour of absorption for the /spl nu//sub 3/ and the /spl nu//sub 4/ transitions at a laser intensity /spl ges/0.1 mW/cm/sup 3/ and the absorption of /spl nu//sub 3/ is very sensitive to the presence of a weak external magnetic field. Meanwhile, there is no hint for this effect both for the extremely thin and the buffer gas-filled cells.
A low-power tunable laser was used to populate the Rb(5P(3/2)) hyperfine-structure levels in a pure optically thick vapour in the presence of a dissipative surface. The retrofluorescence intensities and spectrum profile for the 780 nm (5P(3/2)--> 5S(1/2)) and 795 nm (5P(1/2)-->5S(1/2)) lines were measured and analyzed. The glass-vapor interface was considered as two distinct regions, a wavelength-thickness vapor layer adjacent to the surface and a more remote vapor region The first region was analyzed as a spectral filter that annihilated the absorbed photons and the second one as a rich spectral light source. The authors discussed two possible mechanisms for the 5P(1/2) population in the cell [i.e., mechanism(1): collisions Rb(5P(3/2))+Rb(5S(1/2))-->Rb(5P(1/2))+Rb(5S(1/2)); mechanism(2): collisions Rb(5D)+Rb(5S)-->Rb(5P)+Rb(5P)]. For each one of the possible mechanisms considered, the authors gave the theoretical formulation of the retrofluorescence integrated signal associated with 795 nm(5P(1/2)-->5S(1/2)), which was compared with experiment. Two important characteristic aspects of retrofluorescence spectra must be taken into account when dealing with retrofluorescence signals for atomic process investigation: the retrofluorescence intensity dependence on laser power and sensitized laser retrofluorescence line shapes. When the laser frequency is scanned through the hyperfine resonance line, the sensitized retrofluorescence spectra signal corresponding to the 795 nm line has a profile similar to the profile of the retrofluorescence signal at the 780 nm. The authors have pointed out that mechanism(1) gives the linear dependence of the trtrofluorescence as a function of laser power and the spectrum profile. The population of the 5P(1/2) atomic level in an optically thick vapour can be principally explained by the fine-structure excitation transfer process [mechanism(1)]. It appears from our experimental and theoretical investigations that, the spectral properties of the laser-induced Rb 795 nm sensitized retrofluorescence in a pure optically thick vapour near a dissipative surface cannot be explained by the mechanism(2).
Abstract. We study the Doppler-broadened absorption of a weak monochromatic probe beam in a thermal rubidium vapour cell on the D lines. A detailed model of the susceptibility is developed which takes into account the absolute linestrengths of the allowed electric dipole transitions and the motion of the atoms parallel to the probe beam. All transitions from both hyperfine levels of the ground term of both isotopes are incorporated. The absorption and refractive index as a function of frequency are expressed in terms of the complementary error function. The absolute absorption profiles are compared with experiment, and are found to be in excellent agreement provided a sufficiently weak probe beam with an intensity under one thousandth of the saturation intensity is used. The importance of hyperfine pumping for open transitions is discussed in the context of achieving the weak-probe limit. Theory and experiment show excellent agreement, with an rms error better than 0.2 % for the D2 line at 16.5 ◦ C. PACS numbers: 32.70.-n, 32.70.Fw, 42.62.FiAbsolute Rb absorption 2 1.