This thesis gives an overview of saturation spectroscopy of rubidium and presents new experimental and theoretical results concerning the processes occurring in this type of spectroscopy. Dramatic line intensity variations in the saturation spectrum of Rb85 and Rb87 have been observed when the planes of polarisation of the pump and probe beams were rotated relative to the magnetic field axis. The measurements were performed in magnetic fields of the order of 10 nT. The experimentally obtained results are compared to a new theoretical model. This model could also be used for the analysis of the saturation spectra of other alkali metals. Based on the results obtained, a very sensitive method for the measurement of small magnetic fields is proposed, which is capable of measuring both the direction and magnitude of the magnetic field.
This thesis gives an overview of saturation spectroscopy of rubidium and presents new experimental and theoretical results concerning the processes occurring in this type of spectroscopy. Dramatic line intensity variations in the saturation spectrum of Rb85 and Rb87 have been observed when the planes of polarisation of the pump and probe beams were rotated relative to the magnetic field axis. The measurements were performed in magnetic fields of the order of 10 nT. The experimentally obtained results are compared to a new theoretical model. This model could also be used for the analysis of the saturation spectra of other alkali metals. Based on the results obtained, a very sensitive method for the measurement of small magnetic fields is proposed, which is capable of measuring both the direction and magnitude of the magnetic field.
In this paper, we experimentally study the saturation effect of rubidium atomic magnetic resonance. A pump beam is applied to create atomic spin polarization, a radio frequency (RF) magnetic field is used to drive the spin precession about a static magnetic field, and an off-resonant linearly polarized probe beam is applied to detect the spin dynamics based on the Faraday-rotation effect. When the RF magnetic field intensity becomes strong, a saturation effect is observed. We measure the resonant peak under strong RF magnetic field driving and obtain a saturation dip as an indication of the saturation effect. Furthermore, we show that the line-width of the saturation dip is much smaller than that of magnetic resonance. Accordingly, the sensitivity of the precision measurement based on the saturation dip can be significantly improved. The relations between the saturation dip in the resonant peak and the driving RF magnetic field intensity, as well as pumping intensity, are also studied in our experiment.
In this paper the saturation spectra of rubidium vapour at room temperature, obtained with overlapped co-propagating laser beams, were examined. Unlike the standard saturation spectroscopy, here the transmission of the pump laser beam was detected. The pump laser was locked to an atomic transition of the D2 line, while the probe laser frequency was scanned in a wide frequency range. The pump and probe beams had approximately the same intensities; thus the probe laser can saturate transitions and contribute to optical pumping. This, together with Doppler broadening, leads to rich pump transmission spectra, with many lines appearing due to the interaction of lasers with atoms in different velocity groups. The advantages of this method are well-resolved structures and appearance of spectral lines on a flat, Doppler-free background. Agreement between experimental and theoretical results shows the usefulness of this simple model, based on the rate equations, for identification of lines and determination of relative contribution to the observed line intensity from atoms with different velocities. Theoretical spectra are a useful tool for the calibration of experimental spectra obtained by a nonlinear dependence of the laser frequency on the voltage applied to the piezo used for the laser diode frequency scanning.
Abstract Laser spectroscopy of hot atomic vapours has been studied extensively. Theoretical models that predict the absolute value of the electric susceptibility are crucial for optimising the design of photonic devices that use hot vapours, and for extracting parameters, such as external fields, when these devices are used as sensors. To date, most of the models developed have been restricted to the weak-probe regime. However, fulfilling the weak-probe power constraint may not always be easy, desired or necessary. Here we present a model for simulating the spectra of alkali-metal vapours for a variety of experimental parameters, most distinctly at intensities beyond weak laser fields. The model incorporates optical pumping effects and transit-time broadening. We test the performance of the model by performing spectroscopy of 87Rb in a magnetic field of 0.6 T, where isolated atomic resonances can be addressed. We find very good agreement between the model and data for three different beam diameters and a variation of intensity of over five orders of magnitude. The non-overlapping absorption lines allow us to differentiate the saturation behaviour of open and closed transitions. While our model was only experimentally verified for the D2 line of rubidium, the software is also capable of simulating spectra of rubidium, sodium, potassium and caesium over both D lines.
Zeeman splitting in the D 2 line of rubidium atoms ( 87 Rb and 85 Rb) has been studied using 'Doppler broadened' as well as 'saturation absorption spectroscopy'. While a linearly polarized beam was used for the former experiment, in the latter case a (π, σ ± ) polarization configuration was employed for both pump and probe beams. Zeeman lines have been observed by applying a field up to 5 mT. The field variation of relative line intensities in Doppler-broadened spectrum was determined following Tremblay et al and Nakayama's four-level model. For the saturation spectrum, a four-level model was used. Because the enhancement of absorption at the field is as low as 1 mT, the F g = 2 to F e = 3 transition for 87 Rb can be used as the reference for laser locking. Level crossing is observed in 85 Rb at fields less than 5 mT.
We perform saturated absorption spectroscopy on the D2 line for room temperature rubidium atoms immersed in magnetic fields within the 0.05--0.13 T range. At those medium-high field values the hyperfine structure in the excited state is broken by the Zeeman effect, while in the ground-state hyperfine structure and Zeeman shifts are comparable. The observed spectra are composed by a large number of absorption lines. We identify them as saturated absorptions on two-level systems, on three-level systems in a V configuration, and on four-level systems in an N or double-N configuration where two optical transitions not sharing a common level are coupled by spontaneous emission decays. We analyze the intensity of all those transitions within a unified simple theoretical model. We concentrate our attention on the double-N crossovers signals whose intensity is very large because of the symmetry in the branching ratios of the four levels. We point out that these structures, present in all alkali-metal atoms at medium-high magnetic fields, have interesting properties for electromagnetically induced transparency and slow light applications.
This paper presents a simple analytical theory for the velocity-dependent pump-probe laser spectroscopy of 87Rb and 85Rb atoms where the pump and the probe beams are circularly or linearly polarized. The analytical solutions of the line shapes of the velocity-selective optical pumping spectroscopy [G. Moon and H. R. Noh, Phys. Rev. A 78, 032506 (2008)] and saturated absorption spectroscopy [G. Moon and H. R. Noh, J. Opt. Soc. Am. B 25, 701 (2008); 27, 1741 (2010)] obtained in the previous reports, expressed as a sum of several Lorentzian functions, could be approximated as one (or in some cases, two) Lorentzian function(s). In particular, the contributions of the saturation and optical pumping effects could be discriminated explicitly in these simple analytical solutions, which is not possible in existing theories such as Nakayama's model. The simple analytical results for the saturation spectroscopy were compared with experimental results, and good agreement between them was observed.