Off-Axis Parabolic Mirror

Off Axis Parabolic Mirror for Every Application

An off axis parabolic mirror is an optical device which transforms plane waves into spherical waves and spherical waves into plane waves. This makes it useful for collimating light from a point source as well as focusing collimated light to a point. It does this with high accuracy, and is not dependent on wavelength. Shanghai Optics high quality off-axis parabolic mirrors can be used in broadband UV, visible, and IR applications.

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.

Applications of Off-Axis Parabolic Mirrors

Our OAP metal mirrors are used in spectrometers, interferometers, astronomical optical instruments, spectrum analyzers, and in beam expanders and beam collimators. They can be used in sequence to create a relay system, since with multiple mirrors you can switch between focal plane and pupil plane of your system without degradation in image quality.

Limitations of an Off Axis Parabolic Mirror

Off axis parabolic mirrors should only be used at infinite conjugates. They can produce a perfectly collimated beam from a spherical wave, or diffraction limited imaging when focusing a collimated beam, but when they’re used at finite conjugates the image quality will be abysmal.

While using OAPs it is also important to remember that the orientation matters. If a collimated beam is incident upon the off axis mirror from an off-axis focal angle, it will not produce a diffraction limited image.  If a spherical wave enters on axis, it won’t produce a collimated beam either.

How Are Off-Axis Parabolic Mirrors Produced?

Manufacturers can produce off-axis parabolic mirrors in several ways. One method involves using a rotating furnace to form the mirrors from a molten base material. A simpler way is to cut and shape the off-axis paraboloids from metal blanks. At Shanghai Optics, we use the latter method to produce high-quality standard and custom OAP mirrors quickly.

To provide the best results, we hand-polish our parabolic mirrors from large aluminum blanks and finish them to an accuracy of 1/20 lambda RMS. Our standard mirrors come in diameters between 2.5 and 10 inches and curvatures 15, 30, 45 and 60 degrees off-axis. We also provide off-axis parabolic mirrors in custom sizes and coatings upon request, so you can find an OAP mirror to meet your exact project requirements.

Formula

Off-Axis Parabolic Mirror Factory Standard

An OAP mirror can harness collimated light by positioning a point source or spherical wave at its focal point. Similarly, it can concentrate collimated light to a specific point by directing the light along the optical axis.

Contact us for manufacturing limit or custom specifications

Off-Axis Parabolic Metal Mirrors