This is the G311204331 model from Qioptiq Photonics, a 12.5 mm diameter Double-Convex Lens made of UVFS material with a focal length of 12.5mm. The lens is unmounted and features a high-quality anti-reflection coating, Qio AL RALVIS AOI 45, on both the front and back surfaces to minimize surface reflections and increase transmission.
The lens geometry is characterized by a thickness of 1mm at the edge and 4.7mm at the center. The radii of curvature for the first and second surfaces are 11.548mm and -11.548mm, respectively. The lens is designed to operate at a wavelength of 355nm.
The G311204331 model is a Spherical Lens (Convex-Convex) with a Circular base shape. It is available from Qioptiq Photonics' website, where it is currently in stock. The link to the product page is provided for your convenience.
Please note that this lens is made of UVFS material with the Mal-1965 material ID. The lens is a symmetric convex-convex design, and no inner or outer radius information is provided.