Lenses - Biconcave Lenses
Spherical biconcave lenses of BK7 are mostly used for monochromatic lights, such as laser beams or Fraunhofer lines. These lenses have negative focal length and are used when parallel beams are diverged.
Spherical biconcave lenses of fused silica are mostly used for UV monochromatic lights. Fused silica has almost same performance of transmittance with BK7 in visual and near IR, but has higher performance than BK7 in UV. These lenses have negative focal l