These are components that serve as key enablers for applications requiring high precision and accuracy. They are used in high-precision motion systems, laser cavities, optical interferometers, and metrology devices. Optomechanical components include mounts, plates, kinematic mounts, positioners, flexures, spacers, and more.
These parts are typically made of aluminum or brass and often require precise tolerances and optical finishes to minimize scattering and absorption of light. They also need to have good thermal conductivity for applications in cryogenic environments.
Designing these parts can be difficult because there are many aspects to consider when designing an optomechanical component, including:
- Material properties
The most important aspects to consider when designing an optomechanical component are the material properties of the different elements of the device. The optical material should have a high index of refraction to maximize the reflectivity of the mirrors and the coupling between them. It should also be transparent over a wide range of wavelengths to facilitate coupling between the mirrors and allow a broad range of applications. The mechanical support materials need to be hard and stiff to avoid any damage or strain on critical parts of the device.
The geometry of the optomechanical component is crucial to its performance, especially concerning its use in an application. For example, if certain reflection angles are required for proper operation, those angles need to be considered when designing the mirrors, supports, and spacing between them.
- Surface finishes
Surface finishes are essential in designing an optomechanical component because optical performance is affected by scattering and reflection at interfaces. The surfaces should be smooth (low roughness), free from defects, and have a high-quality polish to reduce smattering and reflection.
Roughness is typically specified in angstroms (10-10 m) or nanometers (10-9 m). Using an atomic force microscope tip, a profilometer can measure roughness to measure surface height variations. A high-quality polish has tiny scratches and pits and low average roughness.
- Thermal considerations
Optomechanical components are often used in high-temperature stability and low thermal noise environments. The thermal properties of the optical mount material (i.e., thermal expansion coefficient) and the compatibility with the ambient conditions should therefore be carefully considered during the design phase.
- Weight and size
A large mass is undesirable for fast and accurate motion and mounting on a vibration-sensitive system such as a laser cavity or interferometer. On the other hand, too small a mass can lead to a stability issue in which the resonant frequency of the optical mount is comparable to that of any external disturbances such as acoustic vibrations, mechanical shock, etc. Careful calculation of the resonant frequency can help determine appropriate dimensions for the optomechanical component.
- Lens design
Several different types of lenses can be used in an optical system. A lens can be used to focus, collimate or diverge light or combine these functions. Each lens type has advantages and disadvantages that need to be considered when designing them into a system. It is crucial to understand how each lens works and determine which one is suitable for your application.
- Resolving power
Resolving power refers to how well a lens can distinguish between two sources closely together in space or time (e.g., two stars separated by only fractions of an arc second). A lens with high resolving power will be able to distinguish between these sources better than one with lower resolving power because light waves passing through different parts of it will interfere
In conclusion, when designing an optomechanical component, it is essential to consider how it will be mounted to its substrate. For components with low CTE materials, amounting to a low-CTE ceramic or metal substrate is often appropriate since they have similar CTEs over much of their operating temperature range. However, for high-CTE materials like glass or metalized plastic, which can have significant differences relative to ceramic and metal substrates even at room temperature, it may be better to use through-holes or standoffs to isolate the component from the substrate that holds it.