Polaris® Low Drift Kinematic Platform Mount

Features

• Machined from Heat-Treated Stainless Steel with Low Coefficient of Thermal Expansion (CTE)
• Mounting Platform with #8 (M4) Through Hole and Array of 8-32 (M4) Tapped Holes
• Hardened Stainless Steel Ball Contacts with Sapphire Seats for Durability and Smooth Movement
• Matched Actuator and Back Plate Provide Smooth Kinematic Adjustment
• Extensive Testing Guarantees <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 Mounting Hole Patterns and Platform Sizes Available by Contacting Tech Support

The Polaris^® Kinematic Platform Mount is the ultimate solution for applications requiring stringent long-term alignment stability. The platform surface features an array of nine 8-32 (M4) tapped holes and one #8 (M4) clearance hole for mounting optomechanical components. Alignment pin holes, located on either side of the clearance hole and two of the taps, allow for precise alignment of components mounted to the surface of the platform.

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, the kinematic platform mount has 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-KIM4(/M) is designed to be compatible with cleanroom and vacuum chamber applications. See the Specs tab and the Design Features tab for details.

Polaris^® Kinematic Mounts Test Data

The Polaris Platform Mounts have undergone extensive testing to ensure high-quality performance. A POLARIS-B1G fixed mount with a mirror glued in was attached to the POLARIS-K1M4 platform mount. This assembly was then mounted to a Ø1" stainless steel post, and then 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 the mount returns the optic, 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 mount tested was raised to 37.5 °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 below, when the Polaris mounts were returned to their initial temperature, the angular position (both pitch and yaw) of the optics 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 a 6 µrad change in the mount's position.

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

Several common factors typically lead to beam misalignment in an optical setup. These include temperature-induced hysteresis of the optic's position, crosstalk, drift, and backlash. Polaris 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 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 optic to its initial position when the initial temperature is restored. All the critical components of the Polaris 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 mount is returned to the initial temperature.

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 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 that very little adjuster lubricant is needed. These adjusters have a smooth feel that allows the user to make small, repeatable adjustments.

Cleanroom and Vacuum Compatibility
The POLARIS-KIM4(/M) is designed to be compatible with cleanroom and vacuum applications. It is chemically cleaned using the Carpenter AAA passivation method to remove sulfur, iron, and contaminants from the surface. After passivation, it is assembled in a clean environment and then 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 LVP High-Vacuum (Krytox) Grease, an ultra-high vacuum compatible, low outgassing PTFE grease, is applied to the adjusters. These features provide high vacuum compatibility and low outgassing performance. 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. Please note that the 8-32 and M4 cap screws included with the Polaris mounts are not rated for pressures below 10^-5 Torr.

Cleanroom-Compatible Packaging
Each vacuum-compatible Polaris mount is packaged within two vacuum bag layers after assembly in a clean environment. The vacuum-tight fit of the bags stabilizes the mount, limiting translation of the front plate due to shocks during transportation. The tight fit also minimizes rubbing against the bag, preventing the introduction of bag material shavings that would contaminate the clean mount.

In the vacuum-sealing process, moisture-containing air is drawn out of the packaging. This eliminates unwanted reactions on the surface of the mount without the need for desiccant materials. The vacuum bags protect the mount from contamination by air or dust during transport and storage, and the double-vacuum bag configuration allows for a straightforward and effective cleanroom entry procedure. The outer bag can be removed outside of the cleanroom, allowing the contaminant-free inner bag to be placed into a clean container and transferred into the cleanroom while retaining the benefits of vacuum-bag packaging. Inside the cleanroom, the mount can be removed from the inner bag when ready for use.

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 Non-Bridging Clamping Arms.

Use a Wide Post
The Polaris' performance is optimized for use with our imperial or metric Ø1" Posts and our POLARIS-CA1 or POLARIS-CA25/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.

Front Plate’s Position
Polaris mounts are 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.

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. In the vertical orientation, the Polaris platform mount can be mounted directly onto a flat surface such as a breadboard using a 8-32 to 1/4"-20 thread adapter (Item # AE8E25E) or M4 x 0.7 to M6 x 1.0 adapter (Item # AE4M6M); the platform cannot be mounted directly to the table horizontally. 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 (Item # LF1P) 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 Polaris mounts below are compatible with the POLARIS-LN1 lock nuts for long-term stability or applications that are exposed to shock and vibration. 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. For applications that require frequent tuning of the adjusters, the lock nuts only need to be lightly tightened by hand to a torque of approximately 4 to 8 oz-in (0.03 to 0.06 N·m). For long term stability, we recommend tightening to a torque of 32 oz-in, which can be achieved by using our TW13 preset torque wrench (sold below). The POLARIS-LN1 lock nuts have a 13 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 right). 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.