16 Figure Figure1a 1a shows a schematic of the ECLD we constructed using a blue LD with a peak wavelength of 457 nm (test sample from Nichia Corporation). The simplification of the laser system at 461 nm achieved in this work would facilitate the Sr laser cooling experiments and is of crucial importance especially for the construction of transportable optical lattice clocks.ĮXTERNAL CAVITY LASER DIODE (ECLD) AT 461 nmįor laser cooling experiments, ECLDs have widely been used since they provide improved frequency tunability and reduced intrinsic linewidths. The obtained dispersion (error) signal, contrary to that obtained by a standard wavelength-modulation (WM) technique, possesses a long tail, which is advantageous for robust frequency locking. We demonstrate, for the first time to our best knowledge, polarization spectroscopy of Sr in a hollow cathode lamp as a modulation-free and hence inexpensive way of frequency stabilization. 15 For spectroscopy of Sr, we adopt a hollow cathode lamp, which provides a Sr vapor with sufficiently large optical density (OD) with a power dissipation of only 3 W. We demonstrate that a blue laser diode can, with the help of injection locking, deliver up to 110 mW of 461 nm light, which is sufficient for Zeeman slowing and magneto-optical trapping of Sr. In this paper, we report the construction of a simple 461 nm light source based on blue laser diodes. Recently, blue laser diodes (LD) operating in the range of 450-460 nm are commercially available. 13 Single-pass periodically poled LiNbO 3 (PPLN) waveguides, which deliver about 80 mW of 461-nm light with a fundamental power of 250 mW, have also been developed. So far, 461-nm light for laser cooling of Sr on the (5 s 2) 1 S 0 → (5 s5 p) 1 P 1 transition has been produced by second-harmonic generation (SHG) using doubling crystals such as KNbO 3, 11 BIBO, 12 and periodically poled KTiOPO 4 (PPKTP). 7, 8 Precise measurement of gravity using Bloch oscillations of Sr atoms in an optical lattice 9 benefited from the very small s-wave scattering length of 88Sr, 10 which is ideal for a variety of atom-optics experiments. Recently, the creation of ultracold Sr 2 molecules in the electronic ground state was realized. The techniques to create quantum degenerate samples of Sr have established for all the stable isotopes ( 84Sr, 2, 3 86Sr, 4 87Sr, 5 and 88Sr 6). The Sr optical lattice clock, 1 where an extremely narrow (∼mHz) intercombination line is used as a clock transition, is now regarded as a candidate for the future redefinition of the second. The range of applications with laser-cooled strontium has tremendously expanded during the past decade.
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