Each mount includes an engraving with the part number, AR coating wavelength, focal length, and the direction of light propagation required to collimate a point source. The doublets are pre-mounted in an aluminum barrel with tight tolerances on lens and barrel diameter to minimize the effects of lens decentering. Please note that these doublets are not achromatic they are designed to provide other advantages of doublets, such as diffraction-limited spot size, to users of high-power lasers. The air-spaced design is also highly resistant to laser damage, since no cement is utilized in the fabrication process. These extra variables allow the performance of these air-spaced doublets to exceed the performance of equivalent cemented doublets in some cases. Air-spaced doublets have two more degrees of freedom than cemented doublets because the interior lens surfaces do not need to have the same curvature. They feature an antireflection coating at the design wavelength (either 532 nm or 1064 nm) that provides excellent transmission when using Nd:YAG lasers. Thorlabs' high-power air-spaced doublets are optimized to provide diffraction-limited performance at either 532 nm or 1064 nm.