For some demanding applications like DUV (deep ultraviolet) lasers, ultra-high power laser systems, and ring laser gyroscopes, high reflection and low scattering loss of the mirrors are some of the most critical factor, where substrates with roughness values down to micros are required to produce the mirrors competent for the applications. 

The super polishing technique is a fabrication technique often utilized to manufacture super-polished mirror substrates for optical applications. Shanghai North Optics has developed an efficient and reliable super-polishing technique through modification the classical super-polishing method, the optical substrates or mirrors produced using our technique feature roughness of less than 1Å on large production scales and guarantee fast despatch for our customers. Our inspection department incorporates an Atom Force Roughness Measuring System and Zygo Interference Flatness Test Instrument, where we implement strict control of qualities. Various superpolished mirror substrates of different materials including BK7, UV fused silica, Zerodur, ZnSe, ZnS, Ge, Si, CaF2, MgF2, and Sapphire are available, in addition to the mirrors for Ring Gyro Lasers.

Although the magnetorheological (MR) fluid polishing technique (where optical surfaces are polished in a computer-controlled magnetorheological finishing slurry) seems a promising approach to achieve finishes of extremely low roughness in the fabrication of optics, its high cost and inefficient production rate make it unpractical for industrial applications. Therefore, most of the super-polished optics are made from conventional and classical polishing methods. A unique modification to the classical polishing technique is developed in North Optics for the production of super-polished mirrors and mirror substrates. In the processing procedure, pitch plates are configured as the mounting tool. North Optics is capable of realizing super polished mirror and mirror substrates of <1Å roughness, 0/0 scratch/dig in the central area, and superior reflection through our state-of-the-art polishing technique.

Inspection Results:

1.  Atom Force Microscope Inspection

Figure1. Roughness of Superpolished Surface Measured by Atom Force Microscope (AFM)
(Fused Silica Substrate with Diameter 200mm, Ra=0.28nm)

2. Zygo Interferometer Inspection

Figure 2. Flatness of Super Polished Surface Measure by Zygo Interferometer

(Fused Silica Substrate of Diameter 300mm, PV=0.101 Wave @633nm)