Diamond Turning Aluminum Mirrors for Optics Applications

Durability, Material, and Composition

At about a third of the density of steel, copper, or brass, by comparison, Aluminum has been historically tricky to polish to an optically reflective surface for use in instrumentation. Aluminum mirrors offer lower cost, quicker fabrication, and excellent natural reflectivity (especially in the infrared range), making them more desirable when compared with glass mirrors. It provides excellent corrosion resistance when used in typical atmospheres, and is readily recycled, making it highly desirable for many types of fabrication.

Beryllium-aluminum alloys are highly stable at extreme temperatures (-65 to 250 degrees F), which makes aluminum optics and mirrors highly desirable for aerospace use. Because of this property, Aluminum and Aluminum alloys are an excellent substitute for coated glass optics.

Fabrication Process

Fabricating with Aluminum can be tricky; however, CMM has the uncommon ability to cut and mill Aluminum optics with precision. We start with a bare block of Aluminum, shaping it into its final form and size, then directly cutting to a high finish using our Single Point Diamond Turning (SPDT) process. Once meticulously created, your optic has the option to be coated.

Because we understand that time to delivery is so critical for our customers, CMM Optic has spent years developing processes for cutting optical surfaces directly into bare aluminum substrates. The new mirror is directly polished using the SPDT process itself and then measured in our state-of-the-art metrology room. The mirror can then either be used bare or coated for UV or IR wavelength ranges for broad bandwidth reflection.

Some optics manufacturers use the India-ink method to process to a precision-finish quality required for life science instrumentation. Ink acts as both the fine polishing compound and a liquid carrier as the surface is polished. 

For applications that require diffraction-limited reflection or just a lower overall surface finish (as low as 1nm rms), CMM can deploy a thin layer of nickel plating on your aluminum mirror design. Keeping aluminum as the substrate material helps keep the weight, cost, and delivery of your optical components low, but the surface quality and durability can be significantly higher due to the increased hardness of the plating. After the final mirror surface is cut into the plating layer, it too can be treated with a variety of thin-film coatings to meet your exacting reflectivity requirements.

Applications for Usage

Aluminum is a commonly found metal. It’s also a desirable foundation for mirror substrates. CMM Optic uses Aluminum to create longwave IR optics, freeform optics, Plano optics, off-axis, folded mirror systems, laser mirror, cylindrical, and aspheric optics. When highly polished, Aluminum is advantageous for wide bandwidth optical mirrors for military and aerospace applications, such as high-altitude UAV surveillance systems and satellite optics.

Aluminum When Creating Optomechanical Components

Bare, passivated, anodized, and powder coated Aluminum parts are commonly used when creating optomechanical assemblies that may range from rails and positions to enclosures, precision mirror mounts, ultrafast laser accessories, or microscopy components.

As an added benefit, when aluminum mechanical components are used in your mechanical assembly in conjunction with aluminum mirrors, the effect of thermal expansion can become far more predictable than using dissimilar materials in your system. When cost and weight are essential factors in determining what material is needed to create precision reflective optics, Aluminum often is the winner. 

More in-depth information on aluminum mirrors can be read on the SPIE website.

If your next project requires Aluminum material, we encourage you to have a conversation with our sales team when selecting a manufacturing vendor. With 20 years of optics and mechanical manufacturing under our belts, CMM Optic offers excellent service with a > 99.9% acceptance rate on delivered orders.