N-BK7 plano-concave lenses are designed to meet demanding laser beam expansion applications.
- N-BK7 optical glass substrates
- ≤λ/4 surface irregularity, 40–20 scratch-dig
- Plano-Concave shape for beam expansion applications
- Broadband or laser line AR coatings available
- Standardized focal lengths across different lens sizes
- RoHS Certified
N-BK7 for VIS and NIR Applications
N-BK7 is an excellent lens material for most visible and near infrared applications. It is the most common borosilicate crown optical glass, and it provides great performance at a good value. Its high homogeneity, low bubble and inclusion content, and straightforward manufacturability make it a good choice for transmissive optics.
High Quality Precision Lens Surfaces
Our precision plano-convex lenses are polished to tight tolerances minimizing wavefront distortion. Tight surface quality tolerances minimize scatter and unwanted diffraction effects. These lenses have a 40-20 scratch-dig surface quality, and a λ/4 surface irregularity.
Broadband Visible Antireflection Coatings
Our AR.14 broadband multilayer antireflection coating markedly improves the transmission efficiency of these lenses by reducing surface reflections over a 430-700 nm wavelength range. This AR coating performs effectively for multiple visible wavelengths and tunable lasers eliminating the need for several sets of optics.
Broadband Multilayer IR Antireflection Coatings
We offer two multilayer AR coatings options for IR and NIR applications. Our AR.16 coating is recommended for NIR applications in the 650-1000 nm range. Our AR.18 coating is for IR applications in the 1000-1550 nm range.
1064 nm Laser Line Antireflection V-Coating
Our AR.33 laser line V-coating offers the lowest reflectance at 1064 nm for maximum transmission while maintaining high durability and high damage resistance. Valuable laser energy is efficiently transmitted through the plano-convex lens rather than lost to surface reflection and scattering. The trade off to its superior performance is the minimal laser line wavelength range.
Standardized Focal Lengths
Standard effective focal lengths provide a systematic approach allowing for lenses of different sizes to be interchanged without requiring other changes to your optical system.
These lenses have been tested for dangerous substances like Pb, Cd, Hg, Hex-Cr, PBB, and PBDE and have been found to be in compliance with RoHS allowable levels.
Plano-Concave Lens Shape for Beam Expansion
Plano-concave lenses are the best choice where object and image are at absolute conjugate ratios greater than 5:1 and less than 1:5 to reduce spherical aberration, coma, and distortion. Plano-Concave lenses bend parallel input rays so they diverge from one another on the output side of the lens and hence have a negative focal length. This is useful for beam expansion applications. The spherical aberration of the Plano-Concave lenses is negative and can be used to balance aberrations created by other lenses. Similar to the Plano-Convex lenses, the curvature surface should face the largest object distance or the infinite conjugate to minimize spherical aberration.