Off-axis Parabolic Mirrors（OAP）

An off-axis parabolic mirror (OAP) focuses a collimated beam or collimated diverging light source in an achromatic manner, with an off-axis design that separates the focal point from the rest of the beam path.The angle between the focused beam and the collimated beam (off-axis angle) is 90°. The propagation axis of the collimated beam should be perpendicular to the base of the substrate to achieve proper focus. Each off-axis parabolic mirror has three threaded mounting holes on the bottom and a non-optical surface that is black anodized and engraved with the focal length for easy identification.

Each off-axis parabolic surface has the ability to focus a collimated beam or collimated broadband point source without chromatic aberration on the original paraboloid . Its total reflection design eliminates the phase delay and absorption losses that would be introduced by transmissive optics. Off-axis parabolic mirrors are suitable for femtosecond laser, UV, visible, IR, and terahertz applications.

Off-axis parabolic mirrors are available in four coatings: UV-enhanced aluminum (250-450nm), silver with a protective coating (450nm-20μm), aluminum with protective coating (450nm-20μm), and gold with or without a protective coating (800nm-20μm) designed for broadband light focusing or collimation.

Features of off-axis parabolic mirrors:

– Protected gold plating by default, with or without silver coating:

– >96% average reflectance over a broadband range of 800 nm – 20 µm

– 1″, 2″ standard in stock, larger sizes such as 3″, 4″, etc. available on request

– Surface roughness: < 150 Å (RMS), custom sizes up to < 20 Å (RMS)

– Effective focal length: 15 mm to 9 inches (228.6 mm)

– Through-hole diameter: greater than 90% of the diameter

Main parameters of off-axis parabolic mirrors:

The main parameters of off-axis parabolic mirrors are: external dimensions, focal length, off-axis angle, coating and Is there a through hole.

1) Dimension

Off-axis paraboloidal metal mirrors are generally prototypes, and the diameter is the form factor. 1 inch (25.4mm) off-axis mirrors are made from 1 inch cylindrical metal cutting and processing, and 2 inch off-axis mirrors are 2 inches (50.4mm) in diameter on the bottom surface.

2) Focal length (reflection focal length, bus focal length)

Off-axis parabolic mirror focal length is divided into reflective focal length and bus focal length, usually the default focal length refers to the reflective focal length, reflective focal length is also usually defined in inches, the focal length of the standard product off-axis mirror is generally 1 inch, 2 inches, 4 inches and 6 inches.

(3) off-axis angle

Off-axis angle is an indicator reflecting the direction of beam propagation through the off-axis parabolic mirror, off-axis parabolic metal reflector off-axis angle is generally 90 °, for the off-axis parabolic mirror off-axis angle of 90 °, collimated beam propagation axis should be perpendicular to the base, so as to achieve the desired focusing effect. If special design is carried out, other off-axis angles can also be set.

4) Coating

Generally, the coating is gold, silver and aluminum. There are also some special coatings, such as UV-enhanced aluminum film.

5）Whether there is a small hole in the center

Off-axis parabolic mirrors with small apertures mainly analyze excitation signals (laser or electron beams) and terahertz waves, for example:

• when two beams need to propagate in space in a common line

②when the center beam or electron beam needs to be left unreflected.

These mirrors have a small central aperture at the base through which the light beam can propagate co-linearly with the beam focused by reflection from the mirror paraboloid. The center hole is typically 3mm in diameter and can be customized upon request.

Standard product of OAP：

    Gold with protective coating：

Silver with protective coating:

Aluminum with protective coating:

UV-enhanced aluminum with protective coating: