REO’s new superpolished laser mirrors offer low loss and can be produced on a number of substrate materials. Their microroughness is <0.5 Å, enabling scattering loss of <5 ppm and finesse of 200,000 when incorporated into optical cavities. Ion beam-sputtered coatings, used to take advantage of the ultrasmooth surfaces, deliver reflectivities of >99.998% at any wavelength in the 450-nm to 2-μm range. The mirrors are supplied with diameters in the 6- to 101-mm range, with a flatness of λ/20 at 633 nm, 10-5 surface quality over an 80% clear aperture, with zero defects (0-0) achievable over controlled subapertures. Typical applications include cavity mirrors in low-gain gas and solid-state HeNe and HeCd lasers, and systems that use nonlinear processes.