Our mirror polishing and gold coating techniques excel at producing mirrors with through holes that have almost zero distortion, or discontinuity with the polished surface. In this example pictured, the hole appeared to make around 1/10 wave of visible distortion. With our chemical gold coating, the inside of the hole is coated and the edges of the hole as well. There is no risk of the coating delaminating, or failing say from humidity ingress.
Mirrors like this are used in chemical sensing, monitoring, or for injecting a beam through the rear of the mirror and out through the face. Careful scrutiny will show the hole appears elliptical, this because the 3mm diameter hole was drilled at 45 degrees.
This was for a research customer who had just been awarded, at very short notice, experimental time on a shared particle physics facility.
We manufactured and shipped two mirrors like this within one week.