Thermal Drift Estimator

Estimate angular drift of kinematic optic mounts from differential thermal expansion between mount body and adjustment screws.

Kinematic optic mounts drift angularly when the mount body and adjustment screws expand at different rates with temperature. The differential coefficient of thermal expansion (ΔCTE = |α_mount − α_screw|) produces a differential linear expansion over the lever arm that tilts the mirror by Δθ = ΔCTE · ΔT radians. For an aluminum mount (23.6 ppm/°C) with stainless screws (17.3 ppm/°C) and a 5 °C temperature change, the resulting angular drift is 31 µrad — large enough to walk a beam off a detector 1 m away by over 60 µm for a reflective optic (where beam deviation = 2× mount tilt). This tool computes differential expansion, angular drift rate in µrad/°C, and beam displacement at a specified target distance for both reflective and transmissive optics. Material presets include aluminum, stainless (300 and 400 series), Invar 36, and Super Invar, with a custom CTE entry for non-standard materials.

Materials
Environment & Geometry

Reflective: beam deviation = 2× mount tilt

Differential Expansion
Differential CTE
|α_mount − α_screw|
6.3000ppm/°C
Differential expansion
Over 25.000 mm lever arm, ΔT = 5.0000 °C
0.78750µm
Angular Drift
Angular drift
For ΔT = 5.0000 °C
31.500µrad
Angular drift rate
Δα = differential CTE
6.3000µrad/°C
Beam Displacement at Target
Beam displacement at 1.0000 m
2× mount tilt (reflective optic)
63.000µm
Assessment
Significant drift — use matched CTE materials or active temperature stabilization.
Abridged Optics — Thermal Drift Estimator v1.0Assumes uniform temperature change and linear expansion. Real drift may differ due to thermal gradients, contact compliance, and mounting preload.

All information, equations, and calculations have been compiled and verified to the best of our ability. For mission-critical applications, we recommend independent verification of all values. If you find an error, please let us know.