69-690 25mm Dia. x 250mm FL; Coated; Si Plano-Convex Lens BBAR 3-5µm

The 69-690 is a 25mm diameter, 250mm focal length plano-convex lens made of silicon, featuring broadband anti-reflection (BBAR) coating on both surfaces for improved transmission in the 3-5µm spectral range. This lens is sourced from Edmund Optics and is currently in stock.

The lens's geometry includes a 2.87mm edge thickness and a 3mm center thickness, with a clear aperture of 25mm. The front surface has a radius of curvature of 604.4mm, while the back surface is planar. The effective focal length (EFL) is 250mm, and the lens is designed to be used in a converging configuration.

This lens is made of silicon, identified by the material ID "silicon sal vil 1957". Silicon is a popular material for infrared (IR) optics due to its low absorption and high refractive index in the IR spectrum. The BBAR coating on both surfaces further enhances the lens's performance by reducing surface reflections, thereby increasing transmission and minimizing ghosting and flaring.

Please note that the coating on this lens is not specified to be vacuum or ion-assisted, which are often used to enhance adhesion and durability. Therefore, it may not be as resistant to environmental conditions or handling as some other coatings.

This lens is a spherical lens, which is the simplest and most common type of lens. Spherical lenses have surfaces that are portions of a sphere, which makes them easy to manufacture and optically efficient. However, they can introduce spherical aberration, which may need to be corrected in certain applications.