We present a simple technique to experimentally determine the optical-path length change with temperature for optical single-mode fibers. Standard single-mode fibers act as natural low-finesse cavities, with the Fresnel reflection of the straight cleaved surfaces being ∼3%, for the laser light coupled to them. By measuring the intensity variations due to interference of light reflected from the fiber front and end surfaces, while ramping the ambient temperature, the thermal sensitivity of the optical-path length of the fiber can be derived. Light was generated by a narrow linewidth, low drift laser. With our fairly short test fibers, we found that it was possible to reach a relative precision of the temperature sensitivity, compared to a reference fiber, on the 0.4%–2% scale and an absolute precision of 2%–5%, with the potential to improve both by an order of magnitude. The results for single-acrylate, dual-acrylate, and copper- and aluminum-coated fibers are presented. Values are compared with analytic models and results from a finite element method simulation. With the aid of these measurements, a simple fiber-interferometer, which is insensitive to thermal drifts, could be constructed.

We demonstrate for the first time the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (gMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a gMOT operating with strontium atoms is optimized and fabricated. We trap 10 6 88 Sr atoms on the 1 S 0 → 1 P 1 transition at 461 nm and transfer 25 % of these atoms to the second cooling stage on the narrower 1 S 0 → 3 P 1 intercombination transition at 689 nm, preparing a sample of 2.5 × 10 5 atoms at 5 µK. These results demonstrate for the first time the applicability of the gMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth based quantum technologies like optical atomic clocks.