Both change the polarization of light. Only one stays accurate when your lab warms up. Here is the difference in plain terms.
Every Tower waveplate ships AR-coated (R < 0.25% per surface standard) with the optical axis marked on the ring. If your wavelength isn't in the stock chart, send us the number — we build custom versions of everything on this site.
Specs to check on any quote
Wavelength (and tolerance band you actually need)
Cemented plates can delaminate. Contacted plates drift. Air spacing removes both failure modes — and improves alignment accuracy.
Tunable laser or wide spectrum? A single material can't hold retardation across hundreds of nanometers. Two materials can.
An uncoated glass surface eats 4% of your beam. Coatings decide what happens to the rest — and how much power they can survive.
