Objective Lens with a Numerical Aperture of 0.4 for Optical Tweezers for Ytterbium Atoms

A wide-aperture objective lens (OL) is developed for experiments with ultracold ytterbium atoms and its characteristics are described. The OL consists of standard models of an aspherical lens and an achromatic doublet, has a numerical aperture of 0.4 and a working distance of 30–35 mm, and is adjusted for a 5‑mm-thick vacuum window. The formation of optical tweezers at a wavelength of 759 nm with a waist radius of 0.92 μm and an image of the optical-tweezers plane at a wavelength of 556 nm with a resolution of several microns has been experimentally demonstrated. The developed OL is simple to manufacture and suitable for use in a wide range of experiments (including those involving thulium atoms), in which the geometry of the vacuum chamber requires the use of an OL with a long working distance.