K9 material is a common choice for focusing and collimating lenses used in laser cutting and welding applications. These lenses are designed to manipulate the laser beam, either by focusing it to a small spot for cutting or by collimating it into a parallel beam for welding. K9 is a popular optical glass material due to its favorable optical properties, including good transmission in the visible and near-infrared spectrum, making it suitable for various laser applications. The precise design and specifications of the lens would depend on the specific requirements of your laser system.