Polaris® Kinematic Glue-In Mirror Mounts

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The POLARIS-K1C4 has a 142° clear edge that allows for low angles of incidence (see the Usage Tips tab). The POLARIS-K05C4 features a 145° clear edge.

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The POLARIS-K19G4 features two cutouts in the glue plane to increase the transmissive clear aperture. The POLARIS-K05G4 and POLARIS-K1G4 also feature these cutouts.

Features

• Machined from Heat-Treated Stainless Steel with Low Coefficient of Thermal Expansion (CTE)
• Glue-In Optic Mount Design for Minimal Optic Distortion
• Hardened Stainless Steel Ball Contacts with Sapphire Seats for Durability and Smooth Movement
• Matched Actuator/Body Pairs Provide Smooth Kinematic Adjustment
• Testing Guarantees <1 μrad Deviation after 12.5 °C Temperature Cycle (See the Thermal Test Data Tab for Details)
• Passivated Stainless Steel Surface Ideal for Vacuum and High-Power Laser Cavity Applications
• Custom Mount Configurations Available by Contacting Tech Support

Polaris^® Kinematic Glue-In Mirror Mounts are the ultimate solution for applications requiring stringent long-term alignment stability.

Optic Mounting
These mounts feature a mounting cell in which an optic can be permanently fixed with an optical adhesive. This mounting technique results in significantly less optical surface distortion than traditional methods based on setscrews or flexure mechanisms. For a tutorial on the use of adhesive to secure an optic to a mount and data demonstrating the minimal wavefront distortion introduced by this process, please see the Optic Installation tab. We also offer Low-Distortion Polaris Kinematic Mirror Mounts that secure optics without the use of an adhesive.

Design
Machined from heat-treated stainless steel, Polaris mounts utilize precision-matched adjusters with ball contacts and sapphire seats to provide smooth kinematic adjustment. As shown on the Thermal Test Data tab, these mounts have undergone extensive testing to ensure high-quality performance. The Polaris design addresses all of the common causes of beam misalignment; please refer to the Design Features tab for detailed information.

Post Mounting
Polaris mirror mounts are equipped with #8 (M4) counterbores for post mounting. Select mounts also include Ø2 mm alignment pin holes around the mounting counterbore, allowing for precision alignments when paired with our Ø1" Posts for Polaris Mirror Mounts. See the Usage Tips tab for more recommendations about mounting configurations.

Cleanroom and Vacuum Compatibility
The Polaris mounts and lock nuts 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.

• When POLARIS-LN1 or POLARIS-LN05 Lock Nuts Are Used
• When the Front Plate is Parallel to the Back Plate
• For 2-adjuster mounts. If you would like a version of this mount with 3 adjusters, please contact Tech Support.
• After 12.5 °C temperature cycle, the beam returns to within 1 μrad of its original position for a Polaris mounted on a Ø1" post. 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.
• Each mount comes 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 Tech Support for details.

Polaris^® Mirror Mounts Test Data

These Polaris Glue-In Kinematic Mirror Mounts have undergone extensive testing to ensure high-quality performance. After mounting a Polaris mount to a Ø1" Post for Polaris Mirror Mounts, the mirror and post assembly was secured to a stainless steel optical table in a temperature-controlled environment. A beam from an independently temperature-stabilized laser diode was reflected by the mirror onto a position sensing detector.

Positional Repeatability After Thermal Shock

Purpose: This testing was done to determine how reliably our glue-in mounts return the mirror, without hysteresis, to its initial position. These measurements show that the alignment of the optical system is unaffected by the temperature shock.

Procedure: The temperature of each mirror mount under test was raised by at least 12.5 °C and maintained for a given soak time. Heat was applied to the front plate of the mount to raise its temperature, which was measured with a thermocouple attached to the bottom of the back plate. Please note that the temperature of the front plate will be slightly higher than what was measured due to the position of the thermocouple on the back plate. After soaking, the temperature of the mirror mount was returned to the starting temperature. The results of these tests are shown below.

Results: As can be seen in the plots in the expandable tables below, when the Polaris mounts were returned to their initial temperature, the angular position (both pitch and yaw) of the mirrors returned to within 1 µrad of its initial position. The performance of the Polaris was tested further by subjecting the mount to repeated temperature change cycles. After each cycle, the mirror’s position reliably returned to within 1 µrad of its initial position.

For Comparison: To get a 1 µrad change in the mount’s position, the 100 TPI adjuster on the Ø1" Polaris mounts 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.

Conclusions: The Polaris Mirror Mounts are high-quality, ultra-stable mounts that will reliably return a mirror to its original position after cycling through a temperature change. As a result, the Polaris mounts are ideal for use in applications that require long-term alignment stability.

Click to Enlarge Click to Enlarge The plot above shows the final angular position of the POLARIS-K05C4 for 10 consecutive thermal shock tests. 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.

Click to Enlarge Click to Enlarge The plot above shows the final angular position of the POLARIS-K05G4 for 10 consecutive thermal shock tests. 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.

Click to Enlarge Thermal Repeatability for Ø19 mm Glue-In Kinematic Mount

Click to Enlarge Click to Enlarge The plot above shows the final angular position of the POLARIS-K1C4 for 10 consecutive thermal shock tests. 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.

Click to Enlarge Click to Enlarge The plot above shows the final angular position of the POLARIS-K1G4 for 10 consecutive thermal shock tests. 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.

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. Our Ø1" and Ø19 mm glue-in Polaris kinematic mirror mounts feature a cell for gluing an optic to the mount. This mounting feature provides maximum stability while minimizing optic distortion for applications like laser cavity construction.

To determine the amount of optic distortion caused by the adhesive mounting process, a ZYGO Phase-Shifting Interferometer was used to measure the wavefront reflected from both unmounted and mounted mirrors. 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 loosely placed on a POLARIS-K1C4 mount without any adhesive. Measurements of the optic distortion were then recorded using the ZYGO interferometer. An optic was then bonded to a POLARIS-K1C4 Ø1" mount and POLARIS-K19G4 Ø19 mm 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.

Results:
As shown in the images below, the surface of the mounted optic exhibited very little distortion. In fact, our testing demonstrated a decrease in the RMS wavefront distortion from 0.010 waves to 0.008 waves when the optic was glued to the Ø1" mount. This result indicates that the optic mounting procedure results in virtually no change to the optical surface. Therefore, the POLARIS-K1C4 and POLARIS-K19G4 mounts are ideal for demanding applications that are sensitive to wavefront distortions.

Loose Optic in POLARIS-K05C4

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Optical Surface Distortion of a Loose Mirror Placed on a POLARIS-K05C4 Mount

Fixed Optic in POLARIS-K05C4

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-K05C4 Ø1" Mount with NOA61 Optical Adhesive

Fixed Optic in POLARIS-K19G4

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-K19G4 Ø19 mm Mount with NOA61 Optical Adhesive

Loose Optic in POLARIS-K1C4

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Optical Surface Distortion of a Loose Mirror Placed on a POLARIS-K1C4 Mount

Fixed Optic in POLARIS-K1C4

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Optical Surface Distortion of a Mirror Fixed in a
POLARIS-K1C4 Ø1" Mount with NOA61 Optical Adhesive

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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 two 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.

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Design Features of the Polaris Glue-In Mounts

Several common factors typically lead to beam misalignment in an optical setup. These include temperature-induced hysteresis of the mirror's position, crosstalk, drift, and backlash. Polaris mirror mounts are designed specifically to minimize these misalignment factors 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 kinematic mirror 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), like stainless steel. However, even mounts made from a material with a low CTE do not typically return the mirror to its initial position when the initial temperature is restored. All the critical components of the Polaris mirror 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; this Polaris mount relies 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.

Crosstalk
Crosstalk is minimized by carefully controlling the dimensional tolerances of the front and back plates of the mount so that the pitch and yaw actuators are orthogonal. In addition, sapphire seats are used at all three contact points. Standard metal-to-metal actuator contact points will wear down over time. The polished sapphire seats of the Polaris mounts, in conjunction with the hardened stainless steel actuator tips, maintain the integrity of the contact surfaces over time.

Drift and Backlash
In order to minimize the positional drift of the mirror mount and backlash, it is necessary to limit the amount of play in the adjuster as well as the amount of lubricant used. When an adjustment is made to the actuator, the lubricant will be squeezed out of some spaces and built up in others. This non-equilibrium distribution of lubricant will slowly relax back into an equilibrium state. However, in doing so, this may cause the position of the front plate of the mount to move. The Polaris mounts use adjusters matched to the body or bushings that exceed all industry standards so very little adjuster lubricant is needed. As a result, alignment of the Polaris mounts is extremely stable even after being adjusted (see the Test Data tab for more information). In addition, these adjusters have a smooth feel that allows the user to make small, repeatable adjustments.

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Polaris Mounts are Shipped Inside Two Vacuum Bag Layers

Vacuum Compatible and Low Outgassing
The Polaris mounts and lock nuts 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 sapphire contacts on the mount are bonded into place using a NASA-approved low outgassing procedure. In addition, DuPont Krytox® LVP High-Vacuum Grease, an ultra-high-vacuum-compatible, low outgassing PTFE grease, is applied to the adjusters. 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, as seen in the image to the right. These vacuum bags do not contain any desiccant materials and tightly wrap the mount preventing 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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When two POLARIS-K1C4 (top) and two POLARIS-K1S4 (bottom) mirror mounts are positioned at the same distance, the clear-edge design of the POLARIS-K1C4 allows more reflections to occur before the beam exits the two-mount system.

Polaris^® kinematic mirror 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 the front and back plates of the 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-CA1 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, the Polaris 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.

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POLARIS-K1C4 Ø1" Mount with a Mounted Optic and Optional POLARIS-N5 Knobs

Mount Alignment
During alignment, minimized deflection will be achieved if the mount's front plate is kept parallel to the base plate. This ensures even thermal expansion of all the adjustment screws, causing the mounted mirror to translate in the Z direction as opposed to rotating during temperature changes.

Front Plate’s Position
Although the mount is designed to allow adjustments of up to 8°, to achieve the best performance, it is recommended that the front plate be kept as parallel as possible to the back plate. This ensures the highest stability of the adjustments.

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.

Use Polaris-Specific Adjustment Tools
We offer stainless steel knobs for most of our Polaris adjusters, either included with the mount or available separately. For Polaris mounts with side hole adjusters, we recommend using the SA1 Side Hole Adjustment Tool, which features a precision-fit tip designed for the side holes to allow backlash-free adjustment. The stainless steel material is chemically cleaned for use in clean setups.

Not Recommended
We do not recommend taking the adjusters out of the body, as it can introduce contamination to the threading, which can consequently reduce the fine adjustment performance significantly. Also, do not pull the front plate away as it might stretch the springs beyond their operating range or crack the sapphire seats.

Adjuster Lock Nuts
POLARIS-LN1 and POLARIS-LN05 lock nuts for the Polaris mounts on this page are available separately below. Lock nuts only need to be lightly tightened to a torque of approximately 4 to 8 oz-in (0.03 to 0.06 N·m). The beam can be held on target with the adjuster thumbscrew or hex key while lightly tightening the lock nut by hand or with a thin-head wrench or cone wrench. To avoid cross threading the lock nut, place it against the adjuster and "unscrew" the lock nut until you feel a slight drop; then thread the lock nut onto the adjuster. Each lock nut is pre-greased with the same ultra-high-vacuum-compatible, low-outgassing PTFE grease as the Polaris mounts and has been tested for adjuster fit.

Low Incidence Angles
The 142° clear edge of the POLARIS-K1C4 mount makes it ideal for applications requiring low angles of incidence. The illustration above shows two Polaris Clear-Edge Mounts with Ø1" mirrors used at a near-normal incidence angle.

Transmissive Clear Aperture
The POLARIS-K05G4, POLARIS-K19G4, and POLARIS-K1G4 have two cutouts in the glue plane. These cutouts increase the clear aperture when using transmissive optics, such as filter or beamsplitters.