Understanding Parabolic Mirrors

A parabolic mirror is a reflector in the shape of a circular paraboloid. Typically made of a highly reflective material such as aluminum, a standard parabolic mirror will center on the vertex of the paraboloid. This is the point where the curvature is greatest, and where the paraboloid is symmetrically divided by its axis. Parabolic mirrors are effective at collecting collimating light and focusing this light to a point, but the receiver will often cast s shadow on the paraboloid’s vertex. This blocks a significant part of the mirror from reflecting light, resulting in substantial signal loss.

Off-axis parabolic mirrors are designed to eliminate this problem. These mirrors are sections of a parent paraboloid that are taken from a point other than the center axis. Depending on how far away from the axis the section originates, an off-axis parabolic mirror may feature a large or a small angle. But since these mirrors focus light to offset points, outside the collection area, there is no issue with receiver shadowing. This makes off-axis parabolic mirrors the optic of choice for long-range and precision instrumentation. The unrestricted  access these mirrors give to the system’s focal point also leads to compact system designs.

• Off-set angle: This denotes the angle between the optical axis and the direction of incoming or outgoing light within the off-axis parabolic mirror.
• Parent focal length: This represents the focal length of an on-axis parabolic mirror that shares the same shape as the off-axis mirror.
• Effective focal length: This indicates the practical focal length of the off-axis parabolic mirror, considering both the offset angle and any deviation from the ideal configuration.

The following factors are also very useful in determining the performance of OAP Mirror:

Protected Coating and Reflective Coatings

For enhanced performance, our mirrors can be coated with a protected aluminium layer, providing durability and improved reflectivity across various wavelengths. Various reflective coatings can be applied to our mirrors, tailored to different spectral regions and application needs.

Coating Options  include:

• Enhanced aluminum coating with 99% reflectivity (for visible spectrum)
• 99% dielectric coating for laser use (visible spectrum)
• UV aluminum/MgF2 coating for laser use (near infrared region)
• Ion plated protected silver coating (for NIR, up to 2 µm)
• Protected gold coating (for 750 nm to far infrared applications)

Chromatic Aberration

OAP mirrors are beneficial in minimizing chromatic aberration since they focus all wavelengths at a single point, enhancing image clarity and accuracy.

Diamond Turned Optical Elements

Our OAP mirrors are diamond turned, a process that ensures high precision and surface quality, critical for demanding optical applications.

Mounting Your Off-Axis Parabolic Mirror

Each mirror has a flat back equipped with three threaded mounting holes for secure attachment. Typically, an adaptor plate is placed between the OAP back surface and a kinematic mirror mount. Given that off-axis mirrors are not rotationally symmetric, rotation around the optical axis must be restricted. Precision machined mounts are recommended for sensitive alignment of the six degrees of freedom.