Off-Axis Parabolic Mirrors and Their Characteristics

An off-axis parabolic mirror is a specialized optical mirror cut from a larger parabolic mirror. Parabolic mirrors collimate light, and an off-axis parabolic (OAP) mirror will do the same, and can also focus incident collimated light to a point.  OAP mirrors are smaller than parabolic mirrors and are easier to incorporate into complex optical systems with minimal obstruction. Their small footprint and unique shape causes the mirror’s focal point to be readily accessible.

By definition, an OAP mirror is cut from the parent parabola at an off-axis: it is not centered on the parent’s optical axis. Because of this, the optical axis of the derivative mirror will be displaced from the optical axis of the parabolic mirror. The focal point, however, will be the same.

Off-set angle: The angle between the optical axis and the direction of the incoming or outgoing light beam in an off-axis parabolic mirror.

Parent focal length: The focal length of the ideal on-axis parabolic mirror with the same shape as the off-axis mirror.

Effective focal length: The actual focal length of the off-axis parabolic mirror, accounting for the offset angle and deviation from the ideal configuration.

Choosing an Off-Axis Parabolic Mirror

Key parameters of an off-axis parabolic mirror are the off-axis angle (OAA), the off-axis distance (OAD), and the focal length. 

Choose an appropriate OAP mirror by deriving the desired reflected focal length from your desired beam diameter. The small angle approximation leads to a very simple relationship between these two parameters:

Beam Diameter = 2 x sin(Θ) x Reflected Focal Length 

Where Θ is the divergent half-angle of the incident light. In fiber optics, when collimating from an optical fiber,  you may replace sin(Θ) by NA (fiber).

How to Use an OAP Mirror

An OAP mirror can be used to derive collimated light from a point source or spherical wave by placing the source or origin of the wave at the OAP mirror’s focal point. It can also be used to focus collimated light to a point by directing the light along the optical axis of the off-axis parabolic mirror.

Factory Standards

Material

Aluminum

Diameter tolerance

+0, -0.2mm

Focal length tolerance

+/- 1 %

Off-axis distance tolerance

+6, -0mm

Surface accuracy

1/10 lambda RMS

Surface Quality

60-40

* Optics design available upon request

 

Type

15° Off-Axis

30° Off-Axis

45° Off-Axis

60° Off-Axis

Diameter

25.40mm

50.80mm

25.40mm

50.80mm

Effective Focal Length (EFL)

387.60mm

54.45mm

148.79mm

135.45mm

Y Offset

3.95mm

27.20mm

4.14mm

4.62mm

*Other sizes and custom coatings are available upon request

Off-Axis Parabolic Metal Mirrors

Focal Length (m)

Diameter, D

Thickness, Te (mm)

Off-Axis distance, OAD (mm)

Off-Axis angle (dgrees)

0.5

2.5inch/63.5mm

15

60

6.9

0.75

3inch/76.2mm

15

80

6.1

1

2.5inch/63.5mm

5

60

3.4

1

4inch/101.6mm

17

110

6.3

1.25

3inch/76.2mm

15

80

3.7

1.25

5inch/127mm

20

100

4.6

1.5

6inch/152.4mm

25

100

3.8

2

4inch/101.6mm

17

110

3.2

2

5inch/127mm

20

100

2.9

2

8inch/203.2mm

33

150

4.3

2.5

10inch/254mm

45

175

4

3

6inch/152.4mm

25

100

1.9

4

8inch/203.2mm

33

150

2.2

5

10inch/254mm

42

175

2

Off-Axis Parabolic Mirrors Coating Specifications

Material Range(um) % Reflection
Protected Aluminum 0.4-0.7 85
Protected Aluminum 0.4-2.0 90
Enhanced Aluminum 0.45-0.65 95
UV Enhanced Aluminum 0.25-0.45 89
UV Enhanced Aluminum 0.25-0.70 85
Protected Gold 0.7-2.0 96
Protected Gold 2.0-10.0 96
Bare Gold 0.7-0.8 94
Bare Gold 0.8-2.0 97
Bare Gold 2.0-12.0 98
Protected Silver 0.45-2.0 98
Protected Silver 2.0-10.0 98
Ultrafast Ehanced Silver 0.6-1.0 99

Off-Axis Parabolic Mirrors at Avantier

At Avantier Inc we produce high-performance off-axis parabolic mirrors for many applications.  A wide variety of coating options are available for these mirrors, including protected gold, protected silver and protected aluminum. For visible and infrared use, protected aluminum is usually a good choice.  We can provide SM-threaded, unthreaded, or post-mountable adaptors. If you are looking for stock Off-Axis Parabolic Mirrors, visit Stock – Off-Axis Parabolic Mirrors.

Our OAP mirrors are diamond turned to provide a smooth mirror surface and a low level of surface roughness.  Contact us today if you’d like to discuss a custom order for an optical mirror with your desired focal length and characteristics.

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