Optoelectronics

Off-axis parabolic mirrors offer near high reflectance

21st August 2020
Alex Lynn

Optical Surfaces has reported that its off-axis parabolic mirrors are particularly suitable for coating using an Ion Beam Sputtering (IBS) technique that provides near 100% reflectivity thereby providing high protection from thermal damage that often arises from high power continuous wave lasers.

Dr Aris Kouris, Sales Director of Optical Surfaces, explained: "Surface microroughness of parabolic mirrors is an important optical quality parameter which describes features which are typically smaller than slope errors. Mirror surface microroughness, when pronounced, will cause effects that may be compared to mild scattering.

“For many applications such effects may not be so critical. However, for high power laser applications using off-axis parabolic mirrors as key focusing elements these effects can play an important role and therefore microroughness needs to be well controlled.

"We have undertaken a long-term study that shows that the proprietary pitch polishing techniques we use to finish off-axis parabolic mirrors produces unmatched low microroughness that do not exceed 1nm RMS. This is particularly important as only ultra-smooth off-axis mirrors can be regularly successfully coated using the ion beam sputtering (IBS) technique and attain nearly 100% reflectance and negligible absorption levels."

Off-axis parabolic mirrors (OAP’s) combine the achromatic and diffraction limited imaging properties of a parabolic mirror with the ability to deviate the light path off-axis, which is useful for most imaging systems. OAP's offer the ability to focus collimated light without introducing spherical aberration.

Additionally, unlike a centred parabolic mirror, an OAP mirror advantageously allows more interactive space around the focal point without disrupting the beam. OAP mirrors are especially suitable for broadband or multiple wavelength high power laser applications.

Using proprietary production techniques, and benefiting from a uniquely stable manufacturing environment, Optical Surfaces’ engineering team produce fast focusing OAP mirrors with surface accuracy, surface microroughness and surface slope errors.

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