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Mounted N-BK7 Bi-Concave Lenses, Uncoated
These Lenses are Also Available in the LSB04 Kit
Thorlabs offers Bi-Concave lenses fabricated from an N-BK7 substrate. N-BK7 is one of the most common types of optical glass used for high quality optical components. It is typically chosen whenever the additional benefits of UV fused silica (i.e., good transmission further into the UV and a lower coefficient of thermal expansion) are not necessary. Since the Abbe Number of N-SF11 (25.76) is lower than that for N-BK7 (64.17), lenses fabricated from N-SF11 will exhibit higher dispersion than those fabricated from N-BK7.
These Ø1/2" and Ø1" lenses are mounted in SM05- (0.535"-40) and SM1- (1.035"-40) compatible mounts, respectively, for compatibility with our line of SM-threaded lens tubes.
Although uncoated lenses are highlighted on this page, these N-BK7 bi-concave lenses are also available with one of three antireflective coatings (-A, -B, or -C), which reduce the amount of light reflected from each surface of the lens over the specified wavelength range. Links to each of these pages can be found in the table below. Please see the Graphs tab for detailed coating curve information. These lenses are also available unmounted.
Bi-concave lenses have a negative focal length and are best used to diverge a converging beam. Similar to a plano-concave lens, a bi-concave lens can diverge a collimated beam to a virtual focus like in a Galilean-type beam expander.
Lens kits with bi-concave lenses made from N-BK7 are available.
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Click Here for Raw Data
Above is the transmission curve for N-BK7, a RoHS-compliant form of BK7. Total Transmission is shown for a 10 mm thick, uncoated sample and includes surface reflections.
The lenses sold on this page are also available with broadband antireflective coatings, the reflectance traces of which are shown in the graph below.
These high-performance multilayer AR coatings have an average reflectance of less than 0.5% (per surface) across the specified wavelength ranges and provide good performance for angles of incidence (AOI) between 0° and 30° (0.5 NA). The plot shown below indicates the performance of the standard coatings in this family as a function of wavelength. Broadband coatings have a typical absorption of 0.25%, which is not shown in the reflectance plots.