Polaris® Fixed Optic Mounts

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The three Polaris glue-in fixed mount designs: optimized for beamsplitters (left), optimized for lenses (middle), and optimized for mirrors (right). The Ø1" versions are shown here.

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Polaris Flexure-Clamp Fixed Mount Optimized for Beamsplitters (Ø1" Version Shown Here)

Features

• Machined from Heat-Treated Stainless Steel with Low Coefficient of Thermal Expansion (CTE)
• Three Fixed Mount Styles for Ø1/2", Ø1", or Ø2" Optics
  • Lens-Optimized with Coarse Focus Adjustment
  • Mirror-Optimized with Clear Edge
  • Beamsplitter-Optimized with Increased Transmissive Clear Aperture
• Glue-In and Flexure-Clamp Optic Mount Designs for Minimal Optic Distortion
• Extensive Testing Guarantees <2 μrad Deviation After 12.5 °C Temperature Cycling (See the Test Data Tab for Details)
• Passivated Stainless Steel Surface Ideal for Vacuum and High-Power Laser Cavity Applications

Polaris^® Fixed Optic Mounts are the ultimate solution for applications requiring stringent long-term alignment stability.

Fixed mounts for plano or curved, Ø1/2", Ø1", or Ø2" optics are available below. The mounts are offered in three styles, each optimized for a different type of optic: lenses, mirrors, or beamsplitters.

Optic Mounting
Polaris Glue-In Optic Mounts feature a mounting cell in which an optic can be permanently affixed with an optical adhesive (available below). This mounting technique results in significantly less optical surface distortion than traditional methods based on setscrews or flexure mechanisms. See the Glue-In Tutorial tab for more information on installing optics in the glue-in mounts. The glue-in mounts on this page can be used with metric-sized optics; however, the optic locating points will not center the optic, requiring the centration to be adjusted by hand during installation. The mounts should not be used with optics that have an outer diameter tolerance greater than zero.

Polaris Flexure-Clamp Optic Mounts provide highly stable mounting without permanently affixing the optic. A monolithic stainless steel flexure clamp and setscrew combination provides temperature-independent retention of the optic with maximum stability and low wavefront distortion. The mounts are designed for optics with imperial diameters; performance will be diminished if these mounts are used with optics with metric diameters. For custom mounts sized for metric optics, please contact Tech Support. 

Design
As shown on the Test Data and Design Features tabs, these Polaris mounts have been extensively developed and tested to ensure high-quality performance by using the proper materials, components, and dimensional specifications. The Polaris design addresses all of the common causes of beam misalignment.

Post Mounting
The Polaris fixed optic mounts are equipped with #8 (M4) counterbores for post mounting. The mounts also feature Ø2 mm alignment pin holes around the mounting counterbore, allowing for precision alignment when paired with our Ø1" Posts for Polaris Mounts. See the Usage Tips tab for more recommendations on mounting configurations.

Cleanroom and Vacuum Compatibility
The Polaris mounts sold on this page are designed to be compatible with cleanroom and vacuum chamber applications. Please see the Specs tab and the Design Features tab for more information on vacuum compatibility.

• All item numbers in the Polaris line start with POLARIS.
• For best performance, use optics with a diameter tolerance of up to +0/-0.1 mm.
• After a temperature cycle, the beam typically returns to within 1 μrad of its original position for a Polaris mounted on a PLS-P150 Ø1" post and POLARIS-CA1 clamping arm. Please see the Test Data tab for details.
• NOA61 is recommended for use with our Polaris mirror mounts because of its excellent glass-metal adhesion and low-stress mounting. However, other UV-curing adhesives are available that provide faster curing times or greater flexibility for environments with large temperature fluctuations. Please see our complete presentation for details.
• This is the recommended torque for mounting a 6 mm thick UVFS optic.
• The POLARIS-B05S mount comes with low-profile 8-32 and M4 cap screws. All other mounts on this page come with standard 8-32 and M4 cap screws.
• This mount is vacuum compatible, assembled in a clean environment, chemically cleaned using the Carpenter AAA passivation method to remove sulfur, iron, and contaminants from the surface, and double vacuum bagged. The 8-32 and M4 cap screws included with the Polaris mount are not rated for pressures below 10^-5 Torr. Contact techsupport@thorlabs.com for details.

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The glue plane is highlighted for each style of glue-in mount above.

Installing an Optic into a Polaris^® Glue-In Mirror Mount

Ensure that there is no grease, dirt, or dust on the optic mounting plane or on the optic itself. Polaris mounts are thoroughly cleaned and then sealed inside two vacuum bag layers to ensure the mounts are free of any contaminants when the package is first opened. If the mount has been handled at all prior to installing the optic, remove any particulates with clean, compressed air and/or clean the mount with acetone or methanol.

Using a clean stainless steel applicator or a syringe, apply a thin coating of optical adhesive to the entire optic glue plane (see photo to the right) in the area where the back surface of the optic will make contact. We recommend Norland Optical Adhesive 61 (item # NOA61, available below).

Then, slide the optic down the optic rim contact points until the back surface of the optic makes contact with the glue. The adhesive can then be cured with a UV curing LED system (Item # CS2010).

Optical Adhesives: We recommend Norland Optical Adhesive 61 (item # NOA61, available below) because of its ease of use. A 10-second pre-cure and a 10-minute final cure provides 3000 psi tensile strength, and the adhesive will maintain its performance over a wide temperature range of -150 °C to +125 °C. We also recommend EPO-TEK 301-2FL for operating temperatures up to 250 °C, at the cost of a slightly weaker bond than the NOA61. Other adhesives may be suitable depending on your application; contact Tech Support for assistance in choosing the appropriate one.

Single Plane Glue Bond: In order to minimize wavefront distortion, the adhesive layer should be confined to a single plane and should not contact the side of the optic. Polaris glue-in mounts offer relief cuts in the glue plane, allowing excess adhesive to flow away from the optic rather than onto the edges. The single plane bond prevents pockets or voids in the glue that reduce the bonding area and weaken the bond. Such pockets or voids are also more susceptible to misalignment due to fluctuations in temperature. In addition, allowing the glue to bond only to the back surface of the optic significantly reduces stress on the optic after the glue is cured.

Temperature while Curing: The temperature of the mount during the UV curing process should be controlled. UV ovens that significantly heat the mount should be avoided because the heat will cause thermal expansion of the mount, adhesive, and optic. Upon cooling, some residual stress will then develop in the glue bond and distort the optic.

See the Test Data tab for details on the low optic distortion provided by these mounts.

Positional Repeatability After Thermal Shock

This testing was done to determine how reliably the mount returns the mirror, without hysteresis, to its initial position so that the alignment of the optical system is unaffected by the temperature shock. During the testing phase, the Polaris mounts were attached to a PLS-P150 Ø1" Post and secured to a stainless steel optical breadboard using a POLARIS-CA1 clamping arm in a temperature-controlled environment. Each mount was secured to the post by an 8-32 cap screw with 16 in-lb of torque. The mirrors were glued in the mounts. The beam from an independently temperature-stabilized diode laser was reflected off the mirror’s surface onto a position sensing detector. 

Procedure:
For these tests, a mirror was used in all mounts, regardless of the mount style. The temperature of each mount tested was raised by at least 10 °C. The elevated temperature was maintained in order to soak the mount at a constant ambient temperature. Then the temperature of the mount was returned to the starting temperature. The results of these tests are shown below.

Results:
The maximum beam deviation of each mount depends on the magnitude of the thermal shock applied to it. However, when the Polaris fixed optic mounts were returned to the initial temperature, the angular position (both pitch and yaw) of the mirrors returned to within 1 µrad of the initial position (within 2 °rad for the POLARIS-C2G). Expand the tables below to see plots showing this data.

For Comparison:
To get a 1 µrad change in the mount’s position, the 100 TPI adjuster on the POLARIS-K1F kinematic mount needs to be rotated by only 0.05° (1/7200 of a turn). A highly skilled operator might be able to make an adjustment as small as 0.3° (1/1200 of a turn), which corresponds to 6 µrad.

POLARIS-L05G

Click to Enlarge Thermal Repeatability for Ø1/2" Glue-In Fixed Mount, Optimized for Lenses

POLARIS-C05G

Click to Enlarge Thermal Repeatability for Ø1/2" Glue-In Fixed Mount, Optimized for Mirrors

POLARIS-B05G

Click to Enlarge Thermal Repeatability for Ø1/2" Glue-In Fixed Mount, Optimized for Beamsplitters

POLARIS-B05S

Click to Enlarge Thermal Repeatability for Ø1/2" Flexure-Clamped Fixed Mount, Optimized for Beamsplitters

Click to Enlarge The plot above shows the final angular position of the POLARIS-B05S for 10 consecutive thermal shock tests. In these tests, the mount temperature was raised to 42 °C over 40 minutes and then allowed to return to ambient temperature. The change in temperature is the difference between the starting temperature and the temperature at the end of the test and includes factors such as the variation in room temperature.

POLARIS-L1G

Click to Enlarge Thermal Repeatability for Ø1" Glue-In Fixed Mount, Optimized for Lenses

POLARIS-C1G

Click to Enlarge Thermal Repeatability for Ø1" Glue-In Fixed Mount, Optimized for Mirrors Click to Enlarge The plot above shows the final angular position of the POLARIS-C1G for 10 consecutive thermal shock tests. In these tests, the mount temperature was raised to 42.5 °C over 50 minutes and then allowed to return to ambient temperature. The change in temperature is the difference between the starting temperature and the temperature at the end of the test and includes factors such as the variation in room temperature.

POLARIS-B1G

Click to Enlarge Thermal Repeatability for Ø1" Glue-In Fixed Mount, Optimized for Beamsplitters Click to Enlarge The plot above shows the final angular position of the POLARIS-B1G for 10 consecutive thermal shock tests. In these tests, the mount temperature was raised to 42.5 °C over 50 minutes and then allowed to return to ambient temperature. The change in temperature is the difference between the starting temperature and the temperature at the end of the test and includes factors such as the variation in room temperature.

POLARIS-B1S

Click to Enlarge Thermal Repeatability for Ø1" Flexure-Clamped Fixed Mount, Optimized for Beamsplitters Click to Enlarge The plot above shows the final angular position of the POLARIS-B1S for 10 consecutive thermal shock tests. In these tests, the mount temperature was raised to 46 °C over 50 minutes and then allowed to return to ambient temperature. The change in temperature is the difference between the starting temperature and the temperature at the end of the test and includes factors such as the variation in room temperature.

POLARIS-C2G

Click to Enlarge Thermal Repeatability for Ø2" Glue-In Fixed Mount, Optimized for Mirrors

Click to Enlarge The plot above shows the final angular position of the POLARIS-C2G for 10 consecutive thermal shock tests. In these tests, the mount temperature was raised to 40 °C over 40 minutes and then allowed to return to ambient temperature. The change in temperature is the difference between the starting temperature and the temperature at the end of the test and includes factors such as the variation in room temperature.

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Preparing a Polaris fixed optic mount for testing with our ZYGO Interferometer.

Optical Distortion Testing Using a ZYGO Phase-Shifting Interferometer

Mounting stresses are responsible for the strain that results in optical surface distortion. Minimizing distortion effects is crucial; any distortion of the optic affects the reflected wavefront. Polaris fixed optic mounts offer maximum stability while minimizing optic distortion for applications like laser cavity construction.

Glue-In Mounts

To determine the amount of optic distortion caused by the adhesive mounting process in our fixed glue-in mounts, a ZYGO Phase-Shifting Interferometer was used to measure the wavefront reflected from both unmounted and mounted mirrors (for testing purposes, a mirror was used in all three mounts). Based on results of the test, we can conclude that our glue-in Polaris mounts introduce a minimum amount of wavefront distortion.

Procedure:
A broadband dielectric mirror was loosely placed on a POLARIS-C1G mount without any adhesive. Measurements of the optic distortion were then recorded using the ZYGO interferometer. The mirror was then bonded to a POLARIS-C1G Ø1" mount using UV-curing Norland Optical Adhesive 61 (Item # NOA61, available below). Additional Zygo measurements of the fixed optic were then recorded to determine the amount of distortion induced by the mounting process. The remaining glue-in mounts were also tested with the optic bonded to the mount.

Results:
As shown in the images below, the surface of the mounted optic exhibited very little distortion. This result indicates that the optic mounting procedure results in virtually no change to the optical surface. Therefore, the Polaris fixed optic mounts are ideal for demanding applications that are sensitive to wavefront distortions.

Fixed Optic in POLARIS-C05G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-C05G Ø1/2" Mount with NOA61 Optical Adhesive

Fixed Optic in POLARIS-L05G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-L05G Ø1/2" Mount with NOA61 Optical Adhesive

Fixed Optic in POLARIS-B05G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-B05G Ø1/2" Mount with NOA61 Optical Adhesive

Loose Optic in POLARIS-C1G

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Optical Surface Distortion of a Loose Mirror Placed on a POLARIS-C1G Mount

Fixed Optic in POLARIS-C1G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-C1G Ø1" Mount with NOA61 Optical Adhesive

Fixed Optic in POLARIS-L1G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-L1G Ø1" Mount with NOA61 Optical Adhesive

Fixed Optic in POLARIS-B1G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-B1G Ø1" Mount with NOA61 Optical Adhesive

Fixed Optic in POLARIS-C2G

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-C2G Ø2" Mount with NOA61 Optical Adhesive

Flexure-Clamped Mounts

To determine the amount of optic distortion exerted on the mirror by the flexure arm, a ZYGO Phase-Shifting Interferometer was used to measure the wavefront distortion at different torque values (see the image below to the left). Based on results of the tests seen below, we recommend a torque of 2 - 3 oz-in for our Ø1/2" flexure-clamped fixed mount, at which the optic wavefront distortion is ≤0.1λ. We recommend a torque of 2 - 4 oz-in to obtain a wavefront distortion of ≤0.1λ for optics in our Ø1" flexure-clamped fixed mount, which was tested using the same method.

Procedure:
A broadband dielectric mirror was installed into a Polaris mount using the setscrew to clamp down the flexure arm. Measurements of the optic distortion were then recorded using the ZYGO interferometer. Once each measurement was complete, the amount of force needed to push the optic out of the mount was measured to check optic retention. The wavefront distortion values shown here give peak-to-valley distortion across the entire optic, representing the worst-case scenario; the center of the optic exhibits significantly less distortion than the edge.

Results:
As seen in the table below, the peak-to-valley wavefront distortion was found to be ≤0.1λ when 2 - 3 oz-in of torque was applied to the setscrew of the POLARIS-B05S Ø1/2" mount.

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POLARIS-B05S Wavefront Distortion for Setscrew Torque of 3 oz-in (See Table to the Right for Other Torque Values)

Several common factors typically lead to beam misalignment in an optical setup. For fixed optic mounts, these include temperature-induced hysteresis of the optic's position. Polaris^® fixed mounts are designed specifically to minimize this misalignment factor and thus provide extremely stable performance. Hours of extensive research, multiple design efforts using sophisticated design tools, and months of rigorous testing went into choosing the best components to provide an ideal solution for experiments requiring ultra-stable performance from a fixed optic mount.

Thermal Hysteresis
The temperature in most labs is not constant due to factors such as air conditioning, the number of people in the room, and the operating states of equipment. Thus, it is necessary that all mounts used in an alignment-sensitive optical setup be designed to minimize any thermally induced alignment effects. Thermal effects can be minimized by choosing materials with a low coefficient of thermal expansion (CTE), such as stainless steel. However, even mounts made from a material with a low CTE do not typically return the optic to its initial position when the initial temperature is restored. Polaris fixed optic mounts are heat treated prior to assembly since this process removes internal stresses that can cause a temperature-dependent hysteresis. As a result, the alignment of the optical system will be restored when the temperature of the mirror mount is returned to the initial temperature.

The method by which the mirror is secured in the mount is another important design factor for the Polaris; these Polaris mounts rely on an adhesive to fix the optic in place. Permanent mounting with optical adhesive reduces optical surface distortion and provides superior performance for applications that are sensitive to wavefront distortion. In addition, this glue-in optic design minimizes temperature sensitivity and limits temperature-dependent hysteresis.

Vacuum Compatible and Low Outgassing
The Polaris mounts sold on this page are designed to be compatible with cleanroom and vacuum chamber applications. They are chemically cleaned using the Carpenter AAA passivation method to remove sulfur, iron, and contaminants from the surface. The 8-32 and M4 cap screws included with each Polaris mount are not rated for pressures below 10^-5 Torr.

Each vacuum-compatible Polaris mount is packaged within two vacuum bag layers after assembly in a clean environment. These vacuum bags do not contain any desiccant materials that produce contamination and tightly wrap the mount, preventing the formation of plastic shavings due to friction against the mount during shipping. This packing method protects the mount from corrosion, gas or liquid contamination, and particulates during transport. The first vacuum bag should be opened in a clean environment while the second vacuum bag should only be opened just prior to installation. When operating at pressures below 10^-5 Torr, we highly recommend using an appropriate bake out procedure prior to installing the mount in order to minimize contamination caused by outgassing.

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View Imperial Product List

Item #	Qty	Description
POLARIS-K1M4	1	Polaris Kinematic Platform Mount, 2 Adjusters, 8-32 Mounting Holes
PLS-P1	1	Ø1" Post for Polaris Mirror Mounts, One 8-32 Tap, L = 1.00"
POLARIS-CA1	1	Flexure Clamping Arm for Ø1" Posts, Non-Bridging, Stainless Steel, 1/4"-20 Clamping Screw
POLARIS-L05G	1	Polaris Ø1/2" Glue-In Fixed Mount, Optimized for Lenses
POLARIS-B05G	1	Polaris Ø1/2" Glue-In Fixed Mount, Optimized for Beamsplitters
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View Metric Product List

Item #	Qty	Description
POLARIS-K1M4/M	1	Polaris Kinematic Platform Mount, 2 Adjusters, M4 Mounting Holes
PLS-P246/M	1	Ø25 mm Post for Polaris Mirror Mounts, One M4 Tap, L = 24.6 mm
POLARIS-CA25/M	1	Flexure Clamping Arm for Ø25 mm Posts, Non-Bridging, Stainless Steel, M6 Clamping Screw
POLARIS-L05G	1	Polaris Ø1/2" Glue-In Fixed Mount, Optimized for Lenses
POLARIS-B05G	1	Polaris Ø1/2" Glue-In Fixed Mount, Optimized for Beamsplitters
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Polaris Glue-In Fixed Optic Mounts on a Kinematic Platform Mount

Polaris^® fixed optic mounts are specifically designed to provide excellent performance under thermal changes and vibrations. Below are some usage tips to ensure that the mount provides optimal performance.

Mounting Options
Due to its relatively low coefficient of thermal expansion, stainless steel was chosen as the material from which to fabricate these Polaris mounts. When mounting a Polaris to a post, we recommend using components fabricated from the same material, such as our Ø1" Posts for Polaris Mirror Mounts and our Polaris Clamping Arm. By choosing components fabricated from the same material as the mount itself, all expansions and contractions will occur at the same rate. In addition, it is best to use the shortest possible post. Alternatively, Polaris mounts can be mounted directly onto a flat surface like a breadboard using a 1/4"-20 to 8-32 thread adapter (Item # AE8E25E) or M6 to M4 thread adapter (Item # AE4M6M), resulting in even better performance. Ensure that the mounting surface is highly flat, polished, and free of debris or scratches.

Polaris Ø1/2" fixed mounts are compact and ideal for space-constrained setups, as shown in the photo to the right.

Polish and Clean the Points of Contact
We highly recommend that the points of contact between the mount and the post, as well as the post and the table, are clean and free of scratches or defects. For best results, we recommend using a polishing stone to clean the table’s surface and a polishing pad for the top and bottom of the post as well as the bottom of the mount.