N-BK7 Plano-Convex Lenses

Name: N-BK7 Plano-Convex Lenses
Brand: PhotonEdge

Key Specifications

Material	N-BK7 (Nd = 1.5168, Vd = 64.2)
Transmission Range	330 - 2,100 nm
Diameter Range	3mm - 150mm
Focal Length Range	5mm - 5,000mm
Surface Quality	40-20 / 20-10 (MIL-PRF-13830B)
Surface Flatness	lambda/4 @ 632.8nm (test plate)
Centration	< 3 arc min
Coating	BBAR / AR @ specific wavelength / Uncoated

Material Options

Select the optimal optical material based on your wavelength, power, thermal environment and mechanical requirements.

N-BK7 — Best value for visible-NIR applications. Excellent optical homogeneity, wide size range availability.
UV Fused Silica — For UV operation below 350nm or high-power laser systems.
SF11 (in Achromatic Doublets) — Pair with BK7 for achromatic correction in imaging systems.

Coating Options

Coatings are engineered around your specific wavelength and operating conditions.

BBAR VIS-NIR — R < 0.5% across 400-1000nm. Maximizes system throughput.
AR @ 532nm — R < 0.1% per surface. For green laser focusing.
AR @ 808/1064nm — For NIR laser diode collimation.
Uncoated — ~4% Fresnel loss per surface. For non-critical applications.

Manufacturing Tolerances

We optimize specifications to match your system requirements — not over-specify. Tighter tolerances increase cost without always improving system performance. Typical manufacturing capabilities:

Surface quality: from 60-40 to 10-5 scratch-dig
Surface flatness: from λ/4 to λ/20 per inch
Dimensional tolerance: ±0.01mm to ±0.05mm
Centration: <3 arc min standard, <30 arc sec precision

Inspection & Quality

Every component undergoes 100% inspection before shipment with full documentation including interferometer reports, spectral curves, surface quality images and dimensional data.

Laser interferometry: λ/100 resolution
Spectrophotometry: 190nm – 25μm
Surface inspection: MIL-PRF-13830B compliant
Dimensional metrology: ±0.01mm accuracy

Applications

General purpose beam focusing and collimation
Imaging systems and relay optics
Machine vision and inspection systems
Laser beam expansion and reduction
Optical sensor focusing elements
Educational and research laboratory optics

Engineering Considerations

Orientation: For focusing a collimated beam, place the curved surface toward the collimated beam (longer conjugate). This minimizes spherical aberration for a singlet lens.

Chromatic aberration: BK7 singlet lenses have significant chromatic aberration. If your system operates across a broad wavelength range and requires sharp focus at all wavelengths, consider achromatic doublets instead.

f-number limit: For f-numbers below f/4, spherical aberration becomes significant in singlet lenses. Consider aspheric lenses for tighter focusing.

Frequently Asked Questions

What is the difference between N-BK7 and standard BK7?

N-BK7 is manufactured to tighter environmental standards (no arsenic) and is the current standard designation. Optically identical to BK7. We recommend specifying N-BK7 for new designs.

When should I upgrade from BK7 to fused silica?

When your application requires UV transmission below 350nm, operation in high-power laser systems, or thermal stability across wide temperature ranges. For standard visible-NIR systems, BK7 offers the best value.

Related Products

BK7 Plano-Convex BK7 Achromatic Doublets BK7 Windows Aspherical Lenses

Related Technical Resources

→ How to Choose the Right Optical Lens → BK7 Plano-Convex vs Bi-Convex Guide