Polaris® SM-Threaded Low Drift Kinematic Mirror Mounts

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Each Polaris mount undergoes extensive thermal testing to ensure high-quality performance. Please see the Test Data tab for additional test results.

Features

• Machined from Heat-Treated Stainless Steel with Low Coefficient of Thermal Expansion (CTE)
• SM-Threaded Bore for Mounting Optics, Lens Tubes, or Other Components
• Hardened Stainless Steel Ball Contacts with Sapphire Seats for Durability and Smooth Movement
• Matched Actuator and Back Plate Provide Stability and Smooth Kinematic Adjustment
• Extensive Testing Guarantees Less than 2 μrad Deviation after 12.5 °C Temperature Cycling (See Test Data Tab for Details)
• Passivated Stainless Steel Surface Ideal for Vacuum and High-Power Laser Cavity Applications
• Custom Mount Configurations are Available by Contacting Tech Support

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

Optic Retention
All of the mounts sold here feature an SM05-threaded (0.535"-40), SM1-threaded (1.035"-40), or SM2-threaded (2.035"-40) bore which allows a variety of optical components to be secured in the mount. Two stainless steel retaining rings are included with each mount; additional retaining rings can also be purchased separately.

Polaris optic bores are precision machined to achieve a fit that will provide optimum beam pointing stability over changing environmental conditions such as temperature changes, transportation shock, and vibration. Performance will be diminished if these mounts are used with optics that have an outer diameter tolerance greater than zero or smaller metric optic sizes (Ø12.5 mm, Ø25 mm, or Ø50 mm).

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 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
The 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. We also recommend using a torque driver or spanner wrench to accurately install the optic and prevent optical surface distortion. See the Usage Tips tab for more recommendations on mounting configurations.

Cleanroom and Vacuum Compatibility
All Polaris mounts on this page are designed to be compatible with cleanroom and vacuum applications. See the Specs tab and the Design Features tab for details.

• All item numbers in the Polaris line start with POLARIS.
• When the front plate is parallel to the back plate.
• After 12.5 °C temperature cycle, the beam returns to within 2 μrad of its original position for a Polaris mounted on a Ø1" post. Please see the Test Data tab for more details.
• The front plate of the mount should be secured when SM-threaded components are being mounted. See the Usage Tips tab for more details.
• The Ø1/2" Mounts come with 8-32 and M4 low-profile cap screws for mounting without obstructing the transmissive beam path. The Ø1" and Ø2" Mounts come with standard 8-32 and M4 cap screws.
• These mounts are 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 mounts are not rated for pressures below 10^-5 Torr. Contact techsupport@thorlabs.com for details.

Polaris^® Mirror Mounts Test Data

All of the Polaris Low-Drift Kinematic Mirror Mounts have undergone extensive testing to ensure high-quality performance. After mounting the Polaris to a Ø1" stainless steel post, 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. The mirror was secured between the two retaining rings included with the Polaris mount, not using epoxy.

Positional Repeatability After Thermal Shock

Purpose: This testing was done to determine how reliably the mount returns 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 tested was raised to 37 °C and maintained for a given soak time. Then 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 2 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 2 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.

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Click to Enlarge The plot above shows the final angular position of the POLARIS-K05T2 for 40 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.

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Click to Enlarge The plot above shows the final angular position of the POLARIS-K1T 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.

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Click to Enlarge The plot above shows the final angular position of the POLARIS-K1T2 for 20 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.

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Click to Enlarge Click to Enlarge The plots above show the final angular position of POLARIS-K2T and POLARIS-K2T1 mounts 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.

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Design Features of the Polaris SM-Threaded 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 such as finite element analysis software, 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; these Polaris mounts offer excellent performance without the use of adhesives. Instead, they have SM05-, SM1-, or SM2-threaded bores and two stainless steel retaining rings that hold the optic in place. The holding force provided by the stainless steel retaining rings is sufficient to keep the mirror locked into place regardless of the ambient temperature. This bore also allows other SM05-, SM1-, or SM2-threaded components to be secured in the mounts.

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 that exceed all industry standards so very little adjuster lubricant is needed. 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

Cleanroom and Vacuum Compatibility
All Polaris mounts, retaining rings, 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. After passivation, they are assembled in a clean environment and double vacuum bagged to eliminate contamination when transported into a cleanroom.

The sapphire contacts 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 the Polaris mounts 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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Spanner Bits and the TD24 Torque Driver Can Be Used to Mount Optics in SM-Threaded Polaris Mirror Mounts

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POLARIS-K1T with Mounted Large Beam Fiber Collimator using the AD15F Thread Adapter

Through thermal changes and vibrations, the Polaris kinematic mirror mounts are designed to provide years of use. Below are some usage tips to ensure that the mount provides optimal performance.

Match Materials
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, we recommend using components fabricated from the same material, such as our Ø1" Posts for Polaris Mirror Mounts and Polaris Clamping Arm.

Use a Wide Post
The Polaris' performance is optimized for use with our Ø1" Posts and our POLARIS-CA1(/M) clamping arm. These posts are made of stainless steel and provide two lines of contact with the mount, which help confine the bottom of the mount during variations in the surrounding temperature, thereby minimizing potential alignment issues.

Optic Mounting
Since an optic is prone to movement within its mounting bore, all optics should be mounted with the Polaris out of the setup to ensure accurate mounting that will minimize misalignment effects. As shown to the right, we recommend using a TD24 torque wrench with either an SPB05, SPB1, or SPB2 Spanner Bit for SM05-, SM1-, or SM2-threaded Polaris mounts, respectively. See the Specs tab for recommended torques. Over torquing the optic retaining rings can result in dramatic surface distortions.

Mounting SM-Threaded Components
Since the front plate of the Polaris mount can move independently from the back plate, it is important to secure the front plate while mounting SM-threaded components. This ensures that the front plate will not rotate with respect to the back plate and crack the sapphire seats at the contact point between the two plates.

Front Plate’s Position
Polaris mounts are designed to allow adjustments of up to 10° for the Ø1/2" mounts, 8° for the Ø1" mounts, and 6.8° for the Ø2" mounts. 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.

Mount as Close to the Table’s Surface as Possible
To minimize the impact of vibrations and temperature changes, it is recommended that your setup has as low of a profile as possible. Using short posts will reduce the Y-axis translation caused by temperature variations and will minimize any movements caused by vibrations. Mount the Polaris directly onto a flat surface such as a breadboard using a 8-32 to 1/4"-20 thread adapter (AE8E25E) or M4 x 0.7 to M6 x 1.0 adapter (AE4M6M). Using this mounting method, the instability introduced by a post will be eliminated.

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 (LFG1P) for the top and bottom of the post as well as the bottom of the mount.

Not Recommended
We do not recommend taking the adjusters out of the body, as it can contaminate the threading. This can 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
The Ø1" and Ø2" Polaris mounts below are compatible with the POLARIS-LN1 lock nuts for long-term stability or applications that are exposed to shock and vibration. POLARIS-LN05 lock nuts are pre-installed onto the adjuster for compatible Ø1/2" Polaris mounts. 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. The POLARIS-LN1 lock nuts have a 13 mm hex and the POLARIS-LN05 lock nuts have a 6 mm hex.

To avoid cross threading the POLARIS-LN1 during installation, place it against the adjuster and "unscrew" the lock nut until you feel a slight drop, then thread the lock nut onto the adjuster (see the animation to the left). 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.