9 July 2013

Supersmooth Mirror Surfaces

Some problems with diamond-machined mirrors
We were asked many times at the Laser Show in Munich, "How do you make your mirrors?” After further discussion we discovered that with higher power lasers and complex systems, diamond-machined mirrors have started to cause problems. The diamond machining process leaves the mirror with a high surface roughness value, and an irregular grating structure.

These surface artefacts cause scatter and diffraction, especially in the near infrared and visible. Sometimes this can reduce the power of a red alignment beam to near zero after a few reflections. In resonators, “mode coupling” of the diffracted radiation causes complex problems in the mode structure. To complicate things more, the roughness and scatter can often be directional, so performance can vary depending on which direction the mirror is mounted.

The image on the right shows the scatter and diffraction from a diamond machined copper mirror reflecting a red laser beam.

Why are our chemically polished mirrors better?
Our chemically polished mirrors have the "super smoothness" needed for very high quality UV grade mirrors. There are no repetitve cutting arcs, or periodic patterns on our polished mirrors. The surface quality is high enough, and the roughness so low, that they can be used in the near IR, the visible, and the UV!

Towards the end of the show, one visitor told us how his spherical diamond machined mirrors continually burnt out in the exact centre of the mirror. With a microscope he saw that the diamond flycutting process had left a tiny "spike" of copper sticking out of the centre. This spike comes from trying to centre any object being flycut 'on axis’. We have seen the same thing on diamond machined mirrors as well.

Very small mirrors for medical applications
Our range of standard mirrors starts at just 5mm diameter, 1mm thick. Gold coated Copper mirrors of this size are ideally suited for, and wellestablished for use with Er:YAG lasers in dental and surgical applications.

They are reflective in both the UV and visible, highly adaptable with long operating lifetimes and have high laser damage resistance. The visible reflectivity of Gold is important because it allows simple alignment of complex multi-mirror systems for dental

Reworking Mounted Mirrors
It can be costly to replace mirrors with mounts, so it is always worth considering reworking. We have the ability to measure the alignment of mirrors that are already mounted. We can then disassemble, polish and coat and reassemble the mirrors, meeting the original specifications of the mirror. This can save €500 or more over the cost of a new mirror and mount.

Industrial Mirrors for Machine Vision
There are some applications that demand our all-metal mirrors because glass mirrors just can’t be used, for example in food or pharmaceuticals manufacture. Our all-metal mirrors, such as Stainless Steel or Aluminium, can be used for barcode scanning, process monitoring and other general machine vision tasks.

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