How Hot Mirror Compares to a beamsplitter in Defense & Aerospace

Every Defense & Aerospace system eventually meets the same question: where does the light go, and how much of it survives the turn? A well-specified Hot Mirror answers…

Every Defense & Aerospace system eventually meets the same question: where does the light go, and how much of it survives the turn? A well-specified Hot Mirror answers both, which is why it earns a place on the bill of materials long before the enclosure is drawn.

At its core, the Hot Mirror is a float or borosilicate glass element carrying a dichroic (transmits visible, reflects IR). That stack is engineered to return incident light efficiently over IR reflect / visible pass, giving designers a predictable, low-loss way to steer a beam where they need it.

Reflection on a first surface is straightforward physics: photons strike the coated face and are returned according to the law of reflection, angle in equals angle out. Because the coating sits on top, there is no second surface behind it to create a faint ghost image, which matters whenever contrast or measurement accuracy is at stake.

Most of the engineering in a Hot Mirror lives in its dichroic (transmits visible, reflects IR). The stack is designed for IR reflect / visible pass and delivers > 90% visible transmit, and its environmental protection layer keeps the metal from tarnishing so the mirror keeps working year after year.

Substrate choice for a Hot Mirror is a trade between optical grade and budget. float or borosilicate glass is a common pick because it can be cut and polished to 4–6λ flatness and a 60-40 surface, which is plenty for the reflection quality most Defense & Aerospace systems require.

A practical Hot Mirror datasheet reads: float or borosilicate glass substrate, 4–6λ flatness, 60-40 quality, 1–3 mm thick, > 90% visible transmit over IR reflect / visible pass. Those five lines settle most design reviews for Defense & Aerospace. See the standard size list for what we stock and what we cut to order.

Where rugged, repeatable optics for harsh environments, a Hot Mirror earns its place by doing one job reliably: turning the beam without adding noise. In Defense & Aerospace that reliability is the difference between a prototype and a shippable product. More application examples are worth a look if the use case is close to yours.

How it compares

Against a plain second-surface mirror, a Hot Mirror removes the ghost by putting the dichroic (transmits visible, reflects IR) up front. Against a dielectric part, a metallic Hot Mirror is cheaper and broader, while giving up a little peak reflectivity. The right call depends on whether your Defense & Aerospace needs > 90% visible transmit at IR reflect / visible pass or ultimate efficiency at a single line.

A short checklist covers most Defense & Aerospace cases: what band (IR reflect / visible pass)? at what angle? how much loss is allowed (> 90% visible transmit)? then pick dichroic (transmits visible, reflects IR) on float or borosilicate glass at 1–3 mm. Getting these four right avoids the most common rework — the application notes show how each sector resolves them.

Mirrors reward careful handling. Hold a Hot Mirror by the edges, keep the coated face away from fingers and aerosols, and clean only with approved optics tissue and solvent when truly needed. Store it in its packaging, coated face protected, and it will hold > 90% visible transmit for years.

Because we control cutting, coating and finishing in one place, a Hot Mirror can move from your drawing to a finished part without hand-offs. The float or borosilicate glass is cut to ±0.01 mm, the dichroic (transmits visible, reflects IR) is vacuum-deposited for > 90% visible transmit over IR reflect / visible pass, and the result is inspected to 4–6λ flatness and 60-40 quality.

Our production of a Hot Mirror follows a simple, repeatable route: laser-cut the float or borosilicate glass to ±0.01 mm, smooth the edges, deposit the dichroic (transmits visible, reflects IR), and inspect to 4–6λ / 60-40. Thickness options span 1–3 mm, and the same Hangzhou line that builds first-surface mirrors also runs windows, substrates and custom coatings.

A Hot Mirror is an optical component built so that reflection happens at the coated front face rather than through a substrate. With a dichroic (transmits visible, reflects IR) on a float or borosilicate glass base, the part delivers > 90% visible transmit reflectivity across IR reflect / visible pass while keeping the useful aperture clean and ghost-free.

Mounting notes

A Hot Mirror is only as good as its mount. Use edge contact rather than clamping the face, avoid over-tightening that bends the float or borosilicate glass and degrades 4–6λ, and keep the coated side clear of adhesive. In Defense & Aerospace a kinematically supported mirror stays aligned through thermal cycles and shipping.

When light meets the Hot Mirror, almost all of it bounces from the front coating. The substrate merely holds the coating in place; it does not need to be traversed by the useful beam, so transmission losses and secondary reflections stay minimal — a real advantage in sensitive Defense & Aerospace setups.

Quick terminology

"Flatness 4–6λ" describes how close the surface is to a perfect plane, in fractions of a wavelength. Tighter flatness costs more but protects wavefront quality, which is why Defense & Aerospace systems specify it explicitly rather than leaving it to chance.

Because we control cutting, coating and finishing in one place, a Hot Mirror can move from your drawing to a finished part without hand-offs. The float or borosilicate glass is cut to ±0.01 mm, the dichroic (transmits visible, reflects IR) is vacuum-deposited for > 90% visible transmit over IR reflect / visible pass, and the result is inspected to 4–6λ flatness and 60-40 quality.

Selecting a Hot Mirror for Defense & Aerospace starts with the wavelength and angle of incidence, then the acceptable loss. Match the dichroic (transmits visible, reflects IR) to IR reflect / visible pass, confirm > 90% visible transmit, and make sure the float or borosilicate glass and 1–3 mm fit the mount you already have. The spec and size tables make that comparison quick.

At JYOPTO we make Hot Mirror parts by cutting float or borosilicate glass with laser accuracy of ±0.01 mm, then applying the dichroic (transmits visible, reflects IR) under vacuum. Standard blanks run 1–3 mm thick, edges are smoothed for safe handling, and every shipped mirror meets 4–6λ flatness with a 60-40 surface — the same disciplines we apply across our optical glass, vacuum-coating and precision cold-processing lines since 2020.

Every Defense & Aerospace system eventually meets the same question: where does the light go, and how much of it survives the turn? A well-specified Hot Mirror answers both, which is why it earns a place on the bill of materials long before the enclosure is drawn.

Wrapping up

A Hot Mirror is a small part with an outsized effect on Defense & Aerospace. Get the dichroic (transmits visible, reflects IR), float or borosilicate glass and flatness right and the rest of the system behaves. If your drawing calls for something specific, the team at JYOPTO can cut and coat it to match — start from the specifications and standard sizes, then tell us the wavelength and angle.