FAQ – Enhanced Aluminum Mirrors
Frequently asked questions about our
SEA-VIS and SEA-NIR mirror series
Go to the data sheet of our Enhanced Aluminum Mirrors
Here you will find our FAQs about our SEA-VIS and SEA-NIR-enhanced aluminum mirrors. If you cannot find the answer to your question here, please feel free to contact us directly with your question. We will be happy to provide you with all available information.
• What advantages do dielectric overcoatings offer?
• Are there standard dimensions?
• Do the mirrors cause ghost images in the optical path?
• Which mirror shape is more economical, round or rectangular?
• Why is the color of the mirror coating blue?
• What is the flatness of the SEA-VIS and SEA-NIR mirrors?
• What is the surface quality of the SEA-VIS and SEA-NIR mirrors?
• Are the SEA mirrors made of solid aluminum?
• How scratch-resistant are the SEA-VIS and SEA-NIR mirrors?
• What is the difference between front surface mirrors and ordinary mirrors?
• Can other glass substrate materials also be coated with the SEA mirror coatings?
• Do you coat metals or plastics with the SEA mirror coatings?
• Do you also coat materials provided by customers with SEA mirror coatings?
• Can I use the SEA front surface mirrors as back surface mirrors?
• What are the reflection characteristics of the mirrors for polarized light?
• What cleaning procedure should I use to clean the mirror coating?
• How heat-resistant are the mirrors?
• For which angles of incidence are the SEA-VIS and SEA-NIR mirrors designed?
• Can I also use the mirrors of the SEA series to reflect a laser beam?
• Do you also offer the 48-hour express service for custom-sized mirrors?
All data and specifications given are average guide values and are not guaranteed.
Also, please consider our "Notes on technical specifications".
Q: What advantages do dielectric overcoatings offer?
A: The enhanced aluminum mirrors in the SEA-VIS and SEA-NIR series both feature a dielectric multilayer thin-film coating applied to a bare aluminum layer. This additional coating system significantly increases optical reflection in the wavelength range for which they are optimized. In addition, the overcoatings, which are only a few nanometers thick, make the mirrors more resistant to scratches and prevent oxidation of the aluminum layer. Therefore, our enhanced aluminum mirrors are significantly more resistant to harsh environmental conditions than many other unprotected metallic coatings. Although the aluminum coating is protected, this does not mean that the mirrors cannot be scratched or damaged. Like all other optics, they must be handled and cleaned with care. However, they are still significantly more robust than the relatively soft silver mirrors or protected aluminum mirror coatings.
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Q: Are there standard dimensions?
A: No, but in most cases it's actually a big advantage. For most of our customers, it is crucial that we are not limited to a few standard sizes. Since each application requires specific dimensions, it is essential for most customers to obtain exactly the mirror size they need. To request a mirror with custom dimensions, please select the desired coating and an available substrate thickness (SEA-VIS: 0.55, 1.00, 2.00, 3.00, 4.00, 5.00, and 6.00 mm / SEA-NIR: 2.00 and 3.00 mm or a custom thickness) in our request form or simply click on the desired thickness in the SEA-VIS and SEA-NIR data sheet to start a request with your preselection. Then enter the desired dimensions of the optics, select a tolerance, and finally enter the desired quantity. You will usually receive our quote on the same business day that we receive your request. The typical delivery time for parts manufactured to customer-specific dimensions is only 1–2 weeks at average capacity utilization in our production facility. This is even possible for several hundred or over a thousand pieces, provided that no complex machining or very tight tolerances are required. For an additional charge, we can often even offer our 48-hour express optics service for custom-made square and round parts.
Q: Do the mirrors cause ghost imaging in the optical path?
A: No! All mirror optics manufactured by us are technical front surface mirrors, also known as first surface mirrors. The reflective coating is therefore located on the front of a flat glass substrate. Unlike with rear-coated mirrors, the image, or light beam to be reflected, does not pass through the glass twice to be reflected. Ghost images caused by secondary reflection from the glass surfaces of a back-coated mirror do not occur when using our high-quality optical front surface mirror series.
Q: Which mirror shape is more economical, round or rectangular?
A: Rectangular shapes are generally more economical to manufacture than round parts, especially for small quantities or small diameters with larger thicknesses. This cost difference decreases significantly with large production volumes but never reaches the same level due to the additional manufacturing steps and the required machine configurations. It also depends on details such as tolerance, dimensions, and thickness. If the permissible tolerance is not too tight and the mirror thickness is low, we could manufacture round parts using CNC precision cutting, which is usually more cost-effective than grinding to diameter. However, if the tolerances are tight or the thickness is greater, the parts must always be ground to diameter. In general, however, a rectangular SEA mirror with moderate tolerances is less expensive to manufacture than a round mirror with a similar diameter and identical tolerances. Large-diameter mirrors are significantly pricier than large rectangular mirrors.
Q: Why is the color of the mirror coating blue?
A: If the optically active surface has a blue color, you have probably forgotten to remove the protective tape from the mirror coating. This blue film protects the mirror during manufacture, transport, and installation. It must be removed before using the mirror. However, not all mirrors have a protective tape. Depending on how they are manufactured, some mirrors might not have a protective film on the coating.
Q: What is the flatness of the SEA-VIS and SEA-NIR mirrors?
A: Although the mirrors are coated onto high-quality mirror substrates, we do not provide specifications regarding the flatness of our standard enhanced aluminum mirrors. However, the flatness is more than sufficient for most technical-optical applications. If you have increased or specific requirements for optical flatness, the mirrors must be custom-made to suit your needs. In such cases, the substrates are first brought to end size and then polished to a defined flatness. The finished substrates are then coated in a separate coating run. Please send us your request if you require a specific flatness and provide us with all relevant details regarding the desired optics.
Q: What is the surface quality of the SEA-VIS and SEA-NIR mirrors?
A: The standard surface quality corresponds to 80-50 scratch and dig according to MIL-0-13830A (cosmetic surface quality) and is our minimum specification. In practice, however, it is usually much better. If you have specific or defined quality requirements, the mirrors must be manufactured individually according to these specifications. This customized manufacturing is carried out using special processing methods and polishing the substrates to a defined surface quality. The mirrors are then coated in a separate coating run. If you require optics with a defined surface quality, please send us your inquiry with all the relevant details.
Q: Are the SEA mirrors made of solid aluminum?
A: No. Both SEA enhanced aluminum mirror series are based on glass substrates coated with a thin, high-purity aluminum layer and an additional multi-layer non-metallic thin-film overcoating that increases the reflectivity. We do not manufacture mirrors made of solid aluminum.
Q: How scratch-resistant are the SEA-VIS and SEA-NIR mirrors?
A: We do not make calls on the scratch resistance of our SEA-VIS and our SEA-NIR mirrors in the form of a specification. However, compared to mirrors without a protective coating or to the soft protected silver or aluminum coatings, both the SEA-VIS and SEA-NIR enhanced aluminum mirror series offer significantly higher scratch resistance. Nevertheless, as it applies to all optics, the SEA-VIS and SEA-NIR mirrors must be handled with care to prevent scratching or other damage.
Q: What is the difference between front surface mirrors and ordinary mirrors?
A: "Normal" mirrors are back surface mirrors. An image or light beam must first pass through the substrate glass to reach the reflective coating of such a mirror. After the coating has reflected the image, it again has to pass through the glass. So, the image has to go through the glass twice to get reflected. Uncoated glasses show a typical reflection of about 4-5% per side in the visible range, which produces secondary images (ghost images) that overlay with the image reflected by the coating, resulting in a blurry picture. Besides, back surface mirrors usually have a significantly lower reflection and poor optical quality. On the other hand, front surface mirrors have their optically active coating directly on top of a substrate. An image does not have to travel through a glass to be reflected. Instead, it is reflected directly, ultimately preventing any secondary reflections and ghost images. Therefore, the image quality of front surface mirrors is always much better than that of rear-coated mirrors. In addition, the optical properties of the substrates we use to manufacture SEA mirrors exhibit far better flatness than the materials typically used for ordinary mirrors.
Q: Can other glass substrate materials also be coated with the SEA mirror coatings?
A: Yes, this is possible with a separate coating batch, provided that the glass material is suitable for the coating process. However, the purchase quantity must be large enough to make a coating run economically viable, as this always represents the smallest possible production quantity. Therefore, small quantities of a customized enhanced aluminum coating cannot be produced at an acceptable cost.
Q: Do you coat metals or plastics with the SEA mirror coatings?
A: No. We only coat glass and similar materials such as glass ceramics.
Q: Do you also coat materials provided by customers with SEA mirror coatings?
A: Yes! However, the prerequisite is that the supplied substrates are uncoated and technically suitable to be deposited with an enhanced aluminum coating. Because optical coatings are done per batch, this option is only possible and reasonable if the required quantity is large enough for at least one coating run.
Q: Can I use the SEA front surface mirrors as back surface mirrors?
A: Yes, that can definitely work. However, the mirrors will have a lower reflectivity and a changed reflection spectrum if used from the backside. Also, when they are used from the backside, most of the technical disadvantages of back-coated mirrors, like ghost imaging and blurry image effects, will occur. Please note that the reflective coating is located on the unprotected outside when you use a front surface mirror as a back-coated mirror.
Q: How high is the reflection of the enhanced aluminum mirrors above and below the specified wavelength range?
A: This is undefined, as our enhanced aluminum coatings are optimized exclusively for the respective wavelength range specified. They are solely checked and tested against the specifications given in their data sheet. Nevertheless, we are happy to provide you with the typical reflection properties outside the defined wavelength ranges without obligation. However, please note that these values are not guaranteed, as the non-process-controlled wavelength areas can vary in reflection from batch to batch.
Q: What are the reflection characteristics of the mirrors for polarized light?
A: Unless otherwise specified, all specifications apply to unpolarized light. We also make no statements regarding possible changes in the polarization plane. However, for large quantities, a mirror coating specially developed for polarized light based on a separate coating batch is possible in many cases.
Q: What cleaning procedure should I use to clean the mirror coating?
A: Basically, the same rules apply as for any other optics. Detailed cleaning instructions are available on request.
Q: How heat-resistant are the mirrors?
A: The SEA-VIS and SEA-NIR enhanced aluminum mirror series were developed for normal operating temperatures. The maximum possible operating temperature depends on the coating design and the substrate used. The SEA-VIS mirrors are based on a float glass substrate selected for optical quality criteria, which can be used at temperatures of up to approx. 120 °C, provided that there is no large temperature gradient or thermal shock. For higher operating temperatures, we recommend using more temperature-resistant glass substrates and a fully dielectric coating.
Q: For which angles of incidence are the SEA-VIS and SEA-NIR mirrors designed?
A: Both mirror series are designed for an angle of incidence of i = 45°. However, since the mirrors are based on a metallic coating, they do not exhibit the extreme angle-dependent reflectivity that is typical of dielectric mirrors. They can often be used at larger or smaller angles if a lower reflection than at the nominal angle of incidence is acceptable. You can find the specifications for the defined angle of incidence for both mirrors in their data sheet under the headline "Reflectance".
Q: Can I also use the mirrors of the SEA series to reflect a laser beam?
A: Yes, but there are limitations. All SEA mirrors can be used to reflect a laser up to a certain maximum energy density. Low-power lasers with a normal beam diameter, such as those used in barcode scanners, are not a problem at all. However, some customers also successfully use SEA mirrors for applications with medium laser power. To find out whether you can use our SEA mirrors with your laser, please let us know the angle of incidence, wavelength, power, and beam diameter of your laser on the mirror. SEA mirrors are not suitable for high-energy laser systems.
Q: Do you also offer the 48-hour express service for custom-sized mirrors?
A: Yes, we do. For most of our standard mirrors, filters, or windows, we offer our 48-hour express service (production and shipping within two business days) for an additional charge. Whether our express service is available depends on the complexity of your parts, dimension tolerance, the quantities required, the current production load, and the necessary setups required for manufacturing your parts. If you are interested in receiving a quote for our 48-hour service, please send us your inquiry. We will immediately check whether our express service is available for the optics you require.
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Last update: August 28, 2025