Tunable laser or wide spectrum? A single material can't hold retardation across hundreds of nanometers. Two materials can.
The plate operates beyond its band too — the retardation change just exceeds spec. Standard retardance tolerance is λ/100 across the band, with a temperature coefficient under λ/500 per °C. Air-spaced versions are standard; cemented and custom ranges on request.
The four standard bands
465–610 nm — visible
Both change the polarization of light. Only one stays accurate when your lab warms up. Here is the difference in plain terms.
Cemented plates can delaminate. Contacted plates drift. Air spacing removes both failure modes — and improves alignment accuracy.
An uncoated glass surface eats 4% of your beam. Coatings decide what happens to the rest — and how much power they can survive.
