Off-axis parabolic mirrors are specialized optical mirrors made from bigger parabolic mirrors. Parabolic mirrors collimate light, while an off-axis parabolic (OAP) mirror does the same while additionally focusing incident-collimated light to a specific spot. Avantier Inc. specializes in providing unique off-axis parabolic mirror design and production solutions for a variety of applications.
OAP mirrors are smaller than parabolic mirrors and can be integrated into sophisticated optical systems with less obstruction. Their modest size and peculiar design make the mirror’s focal point easily accessible.
By definition, it is sliced off-axis from the parent parabola, meaning it is not centered on the parent's optical axis. As a result, the optical axis of the derivative mirror will differ from that of the parabolic mirror. The focal point, however, will remain the same.
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Discover Precision Optics: Large OAP Mirror
Video Credit: Avantier Inc.
The diagram below is an example of focusing collimated light to a single point after it has been reflected on the surface of the off-axis parabolic mirror.
Avantier typically coats an extra layer of gold or silver to boost the reflectance on the reflective surface, ensuring that the customer's application achieves better efficiency.
Three crucial requirements for describing an off-axis parabolic mirror are the offset angle, parent focal length, and effective focal length.
- Off-set angle: The angle formed by the optical axis and the direction of the entering or exiting light beam in an off-axis parabolic mirror
- Parent focal length: The focal length of an ideal on-axis parabolic mirror is of the same form as an off-axis mirror
- Effective focal length: The actual focal length of the off-axis parabolic mirror, adjusted for offset angle and deviation from the ideal setup
Centered Parabolic Mirror: Parallel light rays converge at the central focal point. Off-axis Parabolic Mirror (OAP): Collimated light focused to an off-axis focal point for unobstructed access. Image Credit: Avantier Inc.
- Centered Parabolic Mirror: This figure depicts a conventional parabolic mirror with parallel light rays converging at a single focal point (F). It is ideal for situations where the light source or target is located along the optical axis
- Off-axis Parabolic Mirror (OAP): This diagram shows an OAP mirror that directs collimated light to an off-center focal point, providing unhindered access to the focal plane. It is beneficial when the optical axis must be maintained free of other components or when a large off-axis angle is required
Choosing an Off-Axis Parabolic Mirror
An off-axis parabolic mirror’s key characteristics are the off-axis angle (OAA), off-axis distance (OAD), and focal length.
Select an appropriate OAP mirror by calculating the desired reflected focal length from the desired beam diameter. The small angle approximation produces a relatively simple relationship between these two parameters:
Beam Diameter = 2×sin(Θ) × Reflected Focal Length
Where Θ is the divergent half-angle of the incident light.
In fiber optics, users can substitute sin(Θ) with NA (fiber) when collimating from an optical fiber.
Key parameters of an off-axis parabolic mirror. Image Credit: Avantier Inc.
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How to Use an OAP Mirror?
It can be used to produce collimated light from a point source or a spherical wave by locating the wave's source or origin at its focal point. It can also be used to guide collimated light to a specific place using the optical axis.
Factory Standards. Source: Avantier Inc.
| . |
. |
| Material |
Aluminum |
| Diameter tolerance |
+0, -0.2 mm |
| Focal length tolerance |
+/- 1 % |
| Off-axis distance tolerance |
+6, -0 mm |
| Surface accuracy |
1/10 lambda RMS |
| Surface Quality |
60-40 |
* Optics design available upon request
Source: Avantier Inc.
| . |
. |
. |
. |
. |
| Type |
15° Off-Axis |
30° Off-Axis |
45° Off-Axis |
60° Off-Axis |
| Diameter |
25.40 mm |
50.80 mm |
25.40 mm |
50.80 mm |
| Effective Focal Length (EFL) |
387.60 mm |
54.45 mm |
148.79 mm |
135.45 mm |
| Y Offset |
3.95 mm |
27.20 mm |
4.14 mm |
4.62 mm |
*Other sizes and custom coatings are available upon request
OAP Metal Mirrors. Source: Avantier Inc.
Focal
Length (m) |
Diameter,
D |
Thickness,
Te (mm) |
Off-Axis distance,
OAD (mm) |
Off-Axis
angle (dgrees) |
| 0.5 |
2.5 inch/63.5 mm |
15 |
60 |
6.9 |
| 0.75 |
3 inch/76.2 mm |
15 |
80 |
6.1 |
| 1 |
2.5 inch/63.5 mm |
5 |
60 |
3.4 |
| 1 |
4 inch/101.6 mm |
17 |
110 |
6.3 |
| 1.25 |
3 inch/76.2 mm |
15 |
80 |
3.7 |
| 1.25 |
5 inch/127 mm |
20 |
100 |
4.6 |
| 1.5 |
6inch/152.4 mm |
25 |
100 |
3.8 |
| 2 |
4 inch/101.6 mm |
17 |
110 |
3.2 |
| 2 |
5 inch/127 mm |
20 |
100 |
2.9 |
| 2 |
8 inch/203.2 mm |
33 |
150 |
4.3 |
| 2.5 |
10 inch/254 mm |
45 |
175 |
4 |
| 3 |
6 inch/152.4 mm |
25 |
100 |
1.9 |
| 4 |
8 inch/203.2 mm |
33 |
150 |
2.2 |
| 5 |
10 inch/254 mm |
42 |
175 |
2 |
Coating Specifications. Source: Avantier Inc.
| 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 |
Custom Off-Axis Parabolic Mirror Design & Manufacturing
Avantier Inc. manufactures high-performance OAP mirrors for various applications. These mirrors are available in several types of coatings, including protected gold, protected silver, and protected aluminum. Protected aluminum is often a good choice for visible and infrared applications. Avantier offers SM-threaded, unthreaded, and post-mountable adaptors for every axis mirror in stock.
The OAP mirrors are diamond-turned to offer a smooth mirror surface and minimum surface roughness.
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