This is a Plano-Concave Spherical Lens, type HO-PVL25-20B, manufactured by Holmarc Opto-Mechatronics. The lens has a base shape of a circle and a diameter of 25mm. The center thickness of the lens is 2.5mm. The effective focal length (EFL) of this lens is -500mm, making it a negative or diverging lens.
The lens is made of N-BK7 Schott, a popular optical glass known for its excellent optical properties. The lens is designed to work with a wavelength of 587.6nm. It comes with a BBAR (Broadband Anti-Reflection) coating on both the front and back surfaces, which significantly reduces reflection losses in the spectral region between 400-700nm. This coating enhances the lens's performance in transmitting light, making it suitable for various applications.
The inner radius of the lens is 0mm, and the outer radius is also 0mm, indicating that the lens is a simple Plano-Concave design with one flat and one curved surface. The curvature of the concave surface is specified as -260.808mm.
This lens is available for purchase from the Holmarc Opto-Mechatronics website, and the link provided indicates that it is currently in stock.