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Atomic and Molecular Physics
Published in Walter Fox Smith, Experimental Physics, 2020
In this experiment you will use laser light to make high-resolution absorption measurements on a gas composed of the two naturally occurring isotopes of rubidium, 85Rb (natural abundance 72%) and 87Rb (natural abundance 28%). You will learn the technique of “Doppler-free saturated absorption spectroscopy,” which can reveal energy differences smaller than the natural Doppler broadening of spectral lines, allowing, in the case of Rb, the hyperfine structure of energy levels to be observed. You will apply the Doppler-free technique to the 5S1/2 to 5P3/2 transition at 780 nm in the infrared. Saturated absorption spectroscopy, first developed in the 1970s, and for which the 1981 Nobel Prize was awarded, is now a common high-resolution spectroscopic tool in a variety of laboratory settings, including apparatuses used to produce “optical molasses” and Bose-Einstein condensates. These techniques have led to many important applications, for example, improving the accuracy of atomic clocks, which has led to dramatic improvements in the accuracy of global positioning systems.
Absorption Spectroscopy and Its Implementation
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Absorption spectroscopy is the most “fundamental” type of spectroscopy, often being the first stepping stone for other techniques, like fluorescence spectroscopy. The advent of narrow-bandwidth, tunable lasers in particular gave rise to key developments beyond basic absorption spectroscopy. For example, Doppler-free saturated absorption introduced the capability of unprecedented resolution to reveal spectral details such as fine and hyperfine structure. Many more milestones stand out over the past decades, along the development of new laser sources or novel experimental techniques.
Laser cooling of rubidium atoms in a 2D optical lattice
Published in Journal of Modern Optics, 2018
Chunhua Wei, Carlos C. N. Kuhn
The experiment utilizes external cavity diode lasers (ECDL) locked to an atomic transition using saturated absorption spectroscopy (SAS). The trapping laser (red detuned from the of the D transition hyperfine level) is amplified () then sent through an acoustic-optic modulator using a double-pass setup (DP AOM). The laser mode is then cleaned through of polarization maintaining single-mode (PMSM) fibre, resulting in about of trapping light sent to the glass cell. Immediately after the locking loop, a small amount of light is removed for use as a probe beam in an absorption image system and is capable of being tuned independently of the trapping light using an AOM double-pass set up. The image beam, in the science table, is located horizontally and orthogonal to the horizontal lattice beam. The repump laser () is passed through an AOM, with the first-order diffracted light fibre coupled to the glass cell resulting in a total power of at the science cell.