There are many situations where even the highest quality lens is just not suitable.

High laser powers, harsh industrial environments, or hard to process materials can mean the use of mirrors as focussing optics is the only choice.

There are several possibilities,

Off Axis Paraboloidal (OAP) mirror

In theory these can offer perfect performance, but are not without problems.

Alignment is critical, An Off Axis Parabolic Mirrorsuch mirrors can be 30 times more sensitive than a lens to align properly to the incoming beam. Costs are high, especially in small numbers, and the range of focal lengths are restricted, especially for long focal lengths. It is often not possible to reverse engineer existing OAP mirrors, forcing the user to return to the original equipment supplier for high priced spares.

Laser Beam Products can supply new OAP’s, and are often able to repair used OAP mirrors.

Cylindrical & Spherical mirror

This offers a “straight through” design for a mirror based focus system. Alignment is simple and just about any focal length is possible (over 5”). The mirrors are repairable, reducing costs even further.

Two spherical mirrors

Spherical mirrors cost a fraction of aspherical mirrors such as OAP’s. They are also easily repaired, and alignment is much less critical. Any focal length greater than 5” is possible, up to 1 metre or more.

The performance of the two focus systems here is extremely good, approaching diffaction limited in many situations.