We introduce a miniaturized saturated absorption spectroscopy setup with a microfabricated vapor cell of 1 mm3 interior volume. The system could be used directly to provide a stable optical frequency at 795 nm, 780 nm, 895 nm, or 852 nm by locking a single-mode diode laser to an atomic transition in rubidium or cesium atoms. Furthermore, this setup could easily be extended to other atoms and molecules such as potassium or iodine. Well behaved distributed-feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers are also available at wavelengths around 1.5 m, where they can be used for saturated absorption spectroscopy in acetylene or in the two-photon transition in rubidium. Finally, such a miniature spectroscopy setup could be used to frequency stabilize telecom lasers between 1540 nm and 1590 nm by adding a periodically poled lithium niobate (PPLN) waveguide in front of the Rb of K spectrometer. This idea has been demonstrated in big systems with conversion efficiencies up to 70 %.
Light from a DBR laser at 795 nm wavelength was used to measure a saturated absorption spectrum with the setup described above. With the vapor cell at 45 °C the Doppler-broadened absorption is about 30 %. The spectrum shown in Fig. 2 (a) is for the transitions 5S1/2, F = 2 → 5P1/2, F’ = 1 and 2 in an isotopically enriched 87Rb cell. The two Lamb dips and the cross-over peak in between demonstrate the very good contrast achievable with this tiny spectrometer. The relevant energy level scheme of 87Rb is shown in Fig. 2 (c). Fig. 2 (b) shows a similar spectrum for a cell with a natural mixture of Rb isotopes. The two center peaks correspond to the transitions 5S1/2, F = 2 → 5P1/2 and 5S1/2, F = 3 → 5P1/2 in 85Rb, where the excited-state hyperfine structure is not resolved in the Doppler-broadened case. An energy level diagram of 85Rb can be seen in Fig. 2 (d).
Contact: Svenja Knappe
References:
Fig. 1. (a) Photograph of the microfabricated saturated absorption spectrometer. (b) Schematic of the microfabricated setup, which consists of a vapor cell with two heaters, two polarizing beam splitters, two polarizers, two prisms, two quarter-wave plates, and a photodetector. The laser and control electronics are not shown in the photo, but could be close to the tiny spectrometer or elsewhere.
Fig. 2. (a) Spectrum of the transitions 5S1/2, F = 2 → 5P1/2, F’ = 1 and 2 isotopically enriched 87Rb measured with the microfabricated saturation spectrometer. (b) Saturated absorption spectrum of all D1-line transitions in natural rubidium, measured in a microfabricated vapor cell. (c) Relevant energy level structure of 87Rb. (d) Relevant energy level structure of 85Rb.