Fused silica is the default substrate for demanding optical work, but the JGS1 and JGS2 grades are not interchangeable. Choosing the right one comes down to your wavelength band, fluorescence budget, and cost.
Transmission bands
JGS1 is a synthetic UV grade transmitting from roughly 185 nm, while JGS2 is optimized for the visible and near-infrared.
Deep-UV work
For sources below 250 nm, JGS1 is the safe choice; JGS2 will absorb too strongly.
Fluorescence considerations
Low autofluorescence matters in imaging and diagnostics. JGS1 typically shows lower background under UV excitation.
Cost trade-offs
JGS1 carries a premium. Where the application never sees deep-UV light, JGS2 delivers the same mechanical performance for less.