λ/4 N-BK7 Plano-concave Lenses

Plano-concave Lens is a bulk optical singlet with a flat side and a convex side, which contribute to a negative focal length and a negative spherical aberration. Plano concave lens diverges collimated light beams from a virtual focus and could be used to spread a collimated light beam, increase the focal length of an optical system or condense images. Plano-concave lenses are often incorporated into Galilean beam expanders, also as components to increase the focal length of an optical instrument, or balance out the spherical aberration, improving image qualities. When the absolute conjugate ratio is greater than 5:1(that is, the absolute value of objective distance: image distance), a plano-concave lens is the best type of negative lens to decrease spherical aberration, coma, and distortion. 

N-BK7 glass is a RoHs-compliant borosilicate material prevalent for uses in the visible and NIR spectrum (in particular when it comes to manufacturing precision visible components). NBK7 features high optical homogeneities, great resistance to scratches and injury, and low inclusion content, it is an ideal substitute for UV Fused Silica when high UV transmission is not required, N-BK7 is also an excellent candidate for making high-precision optical lenses.

Hangzhou Shalom EO offers Stocked and Custom NBK7 Plano-concave Lenses with a diameter range of 0.5-300mm, that are competent for various incorporation into laser scanners, remote sensing,  and imaging instruments, fiber lasers, interferometers, etc. The focal lengths of the stocked N-BK7 Plano-concave lenses differ from -25mm to -100mm, while other focal lengths could be customized. These lenses feature lambda/4 irregularities and 40/20 scratch/dig. Each piece of the lens will undergo strict inspection in Shalom EO’s in-house labs before dispatch, to assure tight tolerance and secure your interest. Our inspection procedure includes an in-process checking stage of the optical properties of lenses and a final test of coatings, dimension precisions, and the visual observation of scratch/dig, apertures, inclusions, etc. 

Note that the transmission range of NBK7 is 350-2200mm, with an absorption dip positioned at approximately 2.8 mirco.  To further enhance the transmission of the NBK7 Plano concave lens, Broadband Anti-reflection (BBAR) coatings could be furnished to accommodate the requirements for multi-wavelength and tunable lasers. V coatings, which are a special form of AR coatings that deliver an ultra-low reflection at a narrow band of designed wavelengths are available, too. These coated lenses are in particular advantageous for elevating the efficiencies of complex optical instruments. Besides, Uncoated NBK7 plano-concave lenses are also accessible in Shalom EO.

1. When applied to diverge a collimated light beam, the curved surface should face the light source (Or in other words, the flat side should point to the focal plane you intend to modulate) so that light bends gradually and spherical aberration is reduced to the greatest extent.