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Off-Axis Parabolic Mirrors with Through Holes, UV-Enhanced Aluminum
Ø2", RFL = 2"
Ø2", RFL = 6"
Through Beam is Parallel to Focused Beam
Through Beam is Parallel to Collimated Beam
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After initial fabrication, all of our off-axis parabolic mirrors are finished on our single-point diamond turning machine. Visit our Custom Mirrors tab for more information.
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Base View of Hole Parallel to Collimated Beam
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Back View of Hole Parallel to Focused Beam
Thorlabs' Off-Axis Parabolic (OAP) Mirrors with Holes are designed for applications that require two beams to propagate collinearly through space. Each mirror’s reflective surface can achromatically focus a collimated beam or collimate a point source, while the off-axis design separates the focal point from the rest of the beam path. Two hole orientations are available: parallel to the focused beam or parallel to the collimated beam.
Mirrors with holes that allow a through beam to be combined with a focused reflected beam are denoted by item #s that include an “H.” The Ø8 mm hole in the back of the substrate tapers down to a Ø3 mm hole as it approaches the mirror surface, permitting the through beam to be focused by a lens as it propagates. These mirrors are often used in electro-optic sampling measurements and other pump-probe experiments, such as time-resolved terahertz spectroscopy (TRTS). In these experiments, it is necessary to illuminate the electro-optic crystal with a pump beam passing through the parabola so that it overlaps with the focus of the THz probe beam that is reflected off of the surface of the parabola.
Mirrors with holes that allow a through beam to be combined with a collimated reflected beam are denoted by item #s that include a “V.” The Ø3.2 mm bore is large enough to accept a beam from our HeNe lasers. Due to the hole passing through the base of the part, these mirrors cannot be used with any of our OAP mirror mounting adapters. Instead, our smooth bore mounting adapters can be used to mount these parts.
As with the rest of our off-axis parabolas, these mirrors are segments of a parent paraboloid. They achromatically focus a collimated beam, and their reflective design eliminates phase delays and absorption losses introduced by transmissive optics. This makes them well suited for use with femtosecond pulsed lasers. The angle between the focused beam and the collimated beam (off-axis angle) is 90°. As shown in the diagrams above, the collimated beam should be normal to the base of the substrate to achieve a proper focus. The diamond-turned parabolic surface has a UV-enhanced aluminum coating that provides >90% average reflectance from 250 - 450 nm (see the Graphs tab for a plot of the coating performance).
The OAP mirrors are fabricated using aluminum substrates. The base of each mirror has three tapped mounting holes in a triangle pattern and an alignment hole. For OAP mirrors with holes parallel to the focused beam, the holes in the base can be used with a mounting adapter (see the Mounting Adapters tab for more details). Holes parallel to the collimated beam pass through the base of the OAP mirror, so mounting adapters cannot be used with these parts. The non-optical surfaces are black-anodized and laser-engraved with the item number for easy identification as shown in the image to the right. The interiors of both types of through holes are not anodized.
The shaded regions in the graphs denotes the ranges over which we guarantee the specified reflectance. Please note that the reflectance outside of these bands is typical and can vary from lot to lot, especially in out-of-band regions where the reflectance is fluctuating or sloped.
Excel Spreadsheet with Raw Data for Our Metallic Coatings
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Mounting Adapter Installation
(Smooth Bore Adapter Shown)
The bottom of each off-axis parabolic (OAP) mirror contains three tapped mounting holes in a triangle pattern and an alignment hole. These holes are used to attach our Mounting Adapters, which contain three corresponding counterbore holes or captive screws and an alignment pin (see the image to the right). Together, these features allow our OAP mirrors to be securely mounted. The tapped holes are also useful in OEM applications.
We offer three types of mounting plates for Ø1/2", Ø1", and Ø2" OAP mirrors. The first type is designed to be mounted in any Ø1", Ø2", or Ø3" mirror mount, depending upon the diameter of the OAP mirror. The second type, designed for post mounting, contains an 8-32 (M4) tapped hole on all four sides for direct mechanical compatibility with Ø1/2" Posts. The third type is externally SM threaded for direct compatibility with any of our internally SM-threaded components, such as our rotation mounts. For Ø1" 90° OAP mirrors, the KCB1P(/M) right-angle mount allows for cage system integration. The table below shows all of these options.
Our Ø1/2", Ø1", and Ø2" OAP mirrors can also be adapted to our SM threads by placing them into our SM Thread to Double Bore Adapters. This type of adapter allows rotation of the OAP mirror with respect to the adapter prior to securing its position, whereas when using the SM-threaded adapters offered on this page, the final location of the OAP mirror is dictated either by the threads themselves (when fully threaded into a mount) or by using the provided retaining ring to secure it in place.
For Ø3" OAP mirrors, we offer the SM2MP3 mounting adapter, which contains four 8-32 tapped holes for post mounting and has external SM2 threading for mounting in our SM2-threaded components, such as the K6X2 6-axis kinematic mount.
Alternatively, all of our OAP mirrors may be directly mounted in our Precision Kinematic Mirror Mounts using their outer diameter.
Selecting a Mirror Based on Desired Output Beam Diameter
When using an off-axis parabolic mirror to collimate a point source, selection of the appropriate mirror is often done based on the desired output beam diameter. Beam diameter can be calculated very easily using the divergence half-angle of the incident light (Θ) and the reflected focal length of the OAP mirror. To calculate the beam diameter in the small angle approximation, use the following equation:
Beam Diameter = 2 x sin(Θ) x Reflected Focal Length
If you are collimating from a fiber, the equation can be rewritten as:
Beam Diameter = 2 x NA (Fiber) x Reflected Focal Length
The table below lists the output beam diameter as a function of the reflected focal length of the mirror and the divergence half-angle of the incident light. Not listed here is the diameter of the OAP mirror. The clear aperture of the OAP mirror you select should be larger than the desired beam output diameter.
Custom Off-Axis Parabolic (OAP) and Aspheric Mirrors
Thorlabs' advanced single-point diamond turning capabilities allow us to produce custom OAP and aspheric mirrors in small quantities. We can produce long focal length and large diameter optics, as well as optics with custom shapes.
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We offer OAP mirrors with custom sizes, focal lengths, substrates, coatings, and clearance holes.
In addition to our stock off-axis parabolic (OAP) mirrors, Thorlabs is also capable of manufacturing a variety of custom aspheric mirrors. Our unique single-point diamond turning (SPDT) capabilities allow us to produce these customs in low quantities at prices that are comparable with our stock offerings. As shown in the video to the right, we engage the slow-slide-servo process of our SPDT machine to polish individual off-axis mirrors by synchronizing the rotational position of the spindle with the linear position of the translation axes.
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Toroidal mirrors have two different radii of curvature and are used to image off-axis points without introducing astigmatism.
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Conical mirrors provide 360° of illumination.
This unique manufacturing capability allows us to provide OAP mirrors with custom reflected focal lengths and diameters, including long-focal-length and large-diameter optics that cannot be produced by conventional two-axis machining. In addition, we can produce OAP mirrors with a variety of custom substrates (including copper), custom coatings, and custom hole sizes and shapes. The use of copper substrates and other advanced techniques also allow us to offer OAP mirrors with enhanced finishes that exhibit less surface roughness than our our stock products, resulting in improved wavefront quality.
Our SPDT competency also enables us to produce mirrors with other custom biconic surfaces and aspheric shapes, including on-axis parabolic, conical, and toroidal mirrors. These custom mirror shapes can be used in a wide variety of optical instruments and specialized imaging systems. For example, toroidal mirrors, which are used to image off-axis points without introducing astigmatism, are commonly used in compact Czerny-Turner monochromators. Conical mirrors, on the other hand, are ideal for non-imaging applications that require 360° of uniform illumination.
We are generally able to produce custom OAP mirrors and aspheric mirrors with short lead times. For modifications to an existing part, delivery in 4-6 weeks is standard. For custom shapes and long focal length optics, a 6-8 week lead time is typical. To receive more information or a quote for a custom optic, please contact Tech Support.
Our engineers are available to help manufacture optics for your application.
Customs are available in low quantities at prices that are comparable with our stock catalog products.
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|Diametera||2" (50.8 mm)||2" (50.8 mm)||2" (50.8 mm)||2" (50.8 mm)||2" (50.8 mm)|
|Reflected Focal Length (RFL)a||2" (50.8 mm)||4" (101.6 mm)||6" (152.4 mm)||4" (101.6 mm)||6" (152.4 mm)|
|Parent Focal Lengtha||1" (25.4 mm)||2" (50.8 mm)||3" (76.2 mm)||2" (50.8 mm)||3" (76.2 mm)|
|Hole Orientation||Parallel to Focused Beam||Parallel to Collimated Beamb|
|Hole Diameter||3 mm on Coated Surface
8 mm on Back of Substrate
|3.2 mm (0.13")|
|Thicknessa||2.47" (62.8 mm)||2.47" (62.8 mm)||2.47" (62.8 mm)|
|Reflected Wavefront Error||<λ/2 at 633 nm||<λ/4 at 633 nm||<λ/4 at 633 nm|
|Bottom Mounting Holes||Three 8-32 Tapsc||Three 8-32 Tapsb|
Our Mounting Adapters for Ø2" Off-Axis Parabolic Mirrors provide mounting alternatives to our smooth bore kinematic mirror mounts. Each contains three #8 counterbores that are positioned to align with the 8-32 tapped holes on our Ø2" OAP Mirrors. Please note that these adapters will block the through holes on OAP Mirrors with holes parallel to the collimated beam. Our smooth bore mounting adapters can be used to mount these parts.
The SM2MP OAP Mirror Adapter is externally SM2 threaded (2.035"-40), which allows a Ø2" OAP mirror to be directly mounted to an internally SM2-threaded component. The adapter is designed to allow easy adaptability to a 60 mm cage system as well as SM2-threaded mirror, translation, and rotation mounts. The included SM2RR retaining ring secures the adapter in place when it is threaded into a mount. An SPW604 and SPW801 Spanner Wrench can be used to thread the retaining ring and adapter, respectively. Three low profile 8-32 cap screws and the required 5/64" hex key are provided with each adapter.
The unthreaded MP508P1 OAP Mirror Adapter is sized to fit inside a Ø3" mirror mount, such as the KS3 Mirror Mount shown above. Three standard 8-32 cap screws and the required 9/64" hex key are provided with each adapter.
The MP508P2(/M) OAP Mirror Adapter contains four 8-32 (M4) taps, for post mounting, that orient the OAP mirror at right angles. The distance from the center of the optic to the edge of the mount in the MP508P2 is 1.5" (38.1 mm), allowing for standardized optical axis heights when used with a fixed height post, such as our Ø1" Posts. Please note that the MP508P2(/M) is not compatible with Ø3" mirror mounts, and is instead designed for post mounting. Three standard 8-32 cap screws and the required 9/64" hex key are provided with each adapter.