FAQ – Enhanced Aluminum Front Surface 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 find our FAQ regarding our SEA-VIS and SEA-NIR enhanced aluminum front surface mirrors. If you can't find an answer to a question you might have here, please feel free to contact us with your question directly. We are pleased to share all available information with you.
• What advantage do the dielectric overcoatings offer?
• Are there any 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 surface 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 normal 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 customer-supplied material with the SEA mirror coatings?
• Can I use the SEA front surface mirrors as backside-coated mirrors?
• How is the reflection of the enhanced aluminum coatings above and below the specified ranges?
• 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?
• Can I also use the SEA-Series mirrors with a laser?
• 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 advantage do the dielectric overcoatings offer?
A: The SEA-VIS and SEA-NIR enhanced aluminum mirror series both have a dielectric multilayer thin film overcoating deposited on the top of a bare aluminum layer. This additional coating system considerably increases the optical reflection in the wavelength range the overcoatings are optimized for. Moreover, the only several nanometer-thick overcoatings make the mirrors more resistant against scratching and prevent the aluminum layer from oxidizing. Hence, our enhanced aluminum mirrors are much more resistant against harsh environmental conditions. Hence, enhanced aluminum mirrors are much more resistant against harsh environmental conditions. Of course, this does not mean the mirrors cannot be scratched or damaged. They must be handled and cleaned with care like any other optics. But they are still significantly more rugged than the relatively soft silver or protected aluminum front surface mirror coatings.
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Q: Are there any standard dimensions?
A: No, but in most cases this is actually a big advantage. It is critical to most of our customers that we are not limited to just a few standard sizes. Since every application requires specific dimensions, it is crucial for most customers to get the exact mirror size they need. So, to request a mirror with customized 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 customized thickness) in our inquiry form or simply click on the desired thickness in the SEA-VIS & SEA-NIR data sheet to open the form with your preselection. Then enter the desired dimensions of the optics, select a dimensional tolerance, and finally enter the desired quantity. You will usually receive our quotation on the same working day on which we receive your request. The typical delivery time for parts manufactured to special dimensions at average capacity is only 1–2 weeks, even for several hundred to thousands of pieces, provided that no complex processing or very tight tolerances are required. We can often even offer our 48-hour express optics service for individually dimensioned square and round parts.
Q: Do the mirrors cause ghost imaging in the optical path?
A: No! All the mirror optics we make are technical front surface mirrors, or first surface mirrors, as they are also called. So, the reflecting coating is on the front side of a flat glass substrate. Contrary to usual backside-coated mirrors, the reflected image or light beam does not pass through a glass twice to be reflected. Ghost images that occur due to the secondary reflection from the surface of a backside-coated mirror do not exist when you use our high-quality front-coated mirror series.
Q: Which mirror shape is more economical, round or rectangular?
A: Rectangular shapes are generally more economical than diameter parts, especially for small quantities. This cost difference decreases significantly with large production volumes but never reaches the same level. This depends on the details, of course, but a rectangular mirror with moderate tolerances is usually less expensive to manufacture than a round mirror with a similar diameter and identical tolerances.
Q: Why is the color of the mirror surface blue?
A: If the optically active surface has a blue color, you have probably forgotten to remove the protective film 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 film. Depending on how they are processed, some mirrors do not have a protective film on the coating.
Q: What is the flatness of the SEA-VIS and SEA-NIR mirrors?
A: We don't further specify the flatness of our standard enhanced aluminum mirror series. Nevertheless, the planarity is sufficient for most technical-optical applications. If you have an increased or defined optical flatness requirement, the mirrors must be custom-made according to your needs. In such cases, the substrates are first brought to size and then polished to a defined flatness. The finished substrates are then optically coated in a separate coating run. Please send us your request if you require a defined flatness and inform us about all the relevant details of the optics you want to request.
Q: What is the surface quality of the SEA-VIS and SEA-NIR mirrors?
A: The standard surface quality is 80-50 scratch & dig according to MIL-0-13830A (Cosmetic Surface Quality), and this is a minimum specification. Typically, it is much higher than that. If you have a particular or defined quality requirement, the mirrors must be individually manufactured according to your needs. This custom manufacturing is done through special handling procedures and polishing of the substrates to a defined surface quality. Subsequently, we coat the mirrors 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. They are coated with a thin, high-purity aluminum layer and a thin film overcoating on top of the metal layer. We do not manufacture solid aluminum mirrors.
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 protective coating or to protected silver or aluminum mirrors, both the SEA-VIS and SEA-NIR enhanced aluminum mirror series offer significantly higher scratch resistance. Nevertheless, as it applies to all optics, they must be handled with care to prevent scratching or other damage.
Q: What is the difference between front surface mirrors and normal mirrors?
A: "Normal" mirrors are so-called backside-coated mirrors. An image or light beam must first pass through 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 substrate 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, rear-coated 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 first to be reflected. Instead, it is reflected directly, which ultimately prevents any secondary reflections and ghost images. Therefore, the optical imaging quality of front surface mirrors is substantially better than that achieved with backside-coated mirrors. Moreover, the optical properties of the substrates we use to make the SEA mirrors are far better than the materials typically used for backside-coated 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 as long as the material is suitable. However, the purchase quantity must be sufficient for at least one coating run, as this is 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 solely coat mirror optics on glasses.
Q: Do you also coat customer-supplied material with the SEA mirror coatings?
A: Yes! However, the prerequisite is that the supplied substrates are uncoated and technically suitable to be coated with an enhanced aluminum coating. Because optical coatings are done per batch, this option is only reasonable if the required quantity is large enough for at least one coating run.
Q: Can I use the SEA front surface mirrors as backside-coated mirrors?
A: Yes, this can absolutely 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 backside-coated mirrors, like ghost imaging and blurry image effects, will occur. Please note that the reflective coating is located on the unprotected backside when you use a front surface mirror as a backside-coated mirror.
Q: How is the reflection of the enhanced aluminum coatings above and below the specified areas?
A: This is absolutely unspecified, as the enhanced aluminum coatings are optimized exclusively for the specified wavelength ranges. They are solely checked and tested exclusively for these specifications. Nevertheless, we are happy to provide you with the typical reflection properties outside the defined wavelength ranges without obligation. Please note that these values can never be guaranteed, as these non-process-controlled wavelength ranges can vary 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. For large quantities, a mirror coating specially developed for polarized light based on a separate coating batch is often possible.
Q: What cleaning procedure should I use to clean the mirror coating?
A: Generally, the same rules apply as for all other optics. Detailed cleaning directions 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 different substrate glasses and a fully dielectric coating.
Q: Can I also use the SEA-Series mirrors with a laser?
A: Yes, but there are limitations. All SEA mirrors can be used to reflect a laser up to a particular maximum power density level. Low-power lasers with normal beam diameters, like in scanners, are no problem at all. We also have customers successfully using the SEA mirrors at medium laser powers. To find out whether you can use our SEA mirrors with your laser, please let us know what angle of incidence, wavelength, power, and beam diameter your laser is working with. The 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 optics, 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, the tolerances, the quantities required, the current production capacity, and the necessary preparations for manufacturing your parts. If you are interested in 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: April 23, 2025