Ø1" N-BK7 Best Form Spherical Lenses, Uncoated
|Uncoated N-BK7 Best Form Lenses|
|Design Wavelength||587.6 nm|
|Diameter Tolerance||+0.0 mm / -0.1 mm|
|Index of Refraction||1.5167 at Design Wavelength|
|Surface Quality||10-5 Scratch-Dig|
|Spherical Surface Power||3 Fringes|
|Spherical Surface Irregularity||λ/4|
|Clear Aperture||≥90% of Diameter|
|Focal Length Tolerance||±1% @ Design Wavelength|
- Best Possible Performance from a Spherical Singlet
- Uncoated Design for High Power Applications
- Ideal for High-Power Applications
- Diffraction-Limited Performance at Small Input Diameters
Thorlabs' N-BK7 Best Form lenses are designed to minimize spherical aberration while still using spherical surfaces to form the lens. They are typically employed at infinite conjugates in high-power applications where doublets are not an option. The lenses presented here are uncoated. Versions of our best form lenses are also available with one of three antireflection coatings deposited on both surfaces to reduce the light reflected from each surface of the lens (see table to the right).
For spherical lenses, a given focal length can be produced by more than one combination of the front and back radii of curvature. Each combination of surface curvatures will result in a different amount of abberation caused by the lens (see the Graphs tab). The radius of curvature for each surface of these "best form" lenses has been chosen to minimize the spherical abberation and coma produced by the lens, optimizing it for use at infinite conjugates. This process makes these lenses more expensive than plano-convex or bi-convex lenses, but still significantly less expensive than our premium line of large-diameter, CNC-polished aspheric lenses. Since the lenses are optimized for minimum spot size, they can theoretically reach diffraction-limited performance for small input beam diameters (see the table below for details).
For best performance in focusing applications, place the surface with the shorter radius of curvature (i.e., the more steeply curved surface) towards the collimated source. Lens kits are also available. Please click here for more information.
|Item #||Input Diameter for|
Performance @ 632.8 nm
|Input Diameter for|
Performance @ 1064 nm
|LBF254-040||5.0 mm||6.0 mm|
|LBF254-050||6.0 mm||7.0 mm|
|LBF254-075||8.0 mm||9.5 mm|
|LBF254-100||10.0 mm||11.5 mm|
|LBF254-150||13.5 mm||16.0 mm|
|LBF254-200||17.0 mm||20.0 mm|
Click to Enlarge
for Raw Data
The transmission curve for N-BK7, a RoHS-compliant form of BK7, is shown above. Total Transmission is given for a 10 mm thick, uncoated sample and includes surface reflections.
Lens Shape vs.
The plot to the right shows coma and spherical abberation plotted as a function of the curvature (c) of the front face of the lens for an N-BK7 lens with focal length of 100 mm, the stop set at the front surface of the lens, and a ±20 field. The curvature (c) is related to the more familiar radius of curvature (r) by c = 1/r. The minimum of the spherical abberation almost coincides with the zero coma location. The lens shape where the spherical aberration is at a minimum provides the basis for a "best form" design.