Can BK7 be used for UV applications?

Many overlook BK7 as a viable material for near-UV applications even though it can transmit down to about 300nm. Nonetheless, BK7’s transmission begins to dip around 340nm. There are some variables when it comes to the source of BK7, though it can be recommended for use above 350nm. When in doubt, sapphire and UV fused silica are the best options, they offer high transmission from UV to visible to NIR wavelengths.