Design of a compact high resolution imaging system for cold atom experiments

Abstract

In cold atom experiments, high resolution imaging systems have been used to extract in-situ density information when studying quantum gases, which is one of the hot topics in this field. Such a system is usually called 'quantum-gas microscope'. To achieve a long working distance and large magnification, high resolution imaging of cold atoms through a vacuum window typically demands a long distance between the atoms and the camera. However, implementing a long imaging system can be difficult due to the space constraints posed by a large number of nearby optical elements, which is a common situation in cold atom experiments. Here we present an imaging system that enables achieving a short distance between the atoms and the image plane with diffraction-limited 1 μm resolution and 50 magnification. The telephoto lens design is adopted to reduce the back focal length and enhance the pointing stability of the imaging lens. The system is optimized at an operating wavelength of 767 nm and corrects aberrations induced by a 5 mm thick silica vacuum window. At a working distance of 32 mm, a diffraction-limited field of view of 408 μm is obtained. The simulation shows that by changing the air spaces between lenses, our design operates across a wide range of window thicknesses (0-15 mm), which makes it robust to apply in typical labs. This compact imaging system is made from commercial on-shelf Φ2" singlets and consists of two components:a microscope objective with a numerical aperture of 0.47 and a telephoto objective with a long effective focal length of 1826 mm. Both are infinity-corrected, allowing the distance between them to be adjusted to insert optical elements for irradiating atoms with laser beams of different wavelengths without impairing the imaging resolution. Taking the manufacturing and assembling tolerances into consideration, the Monte Carlo analyses show that more than 95% of the random samples are diffraction-limited within the field of view. This high success rate ensures that the two objectives can be easily implemented in the experiment. Together with its performance with other wavelengths (470-1064 nm), this imaging system can be used for imaging different atom species, such as sodium, lithium, and cesium.