What Is a Protected Gold Mirror? A Optical Metrology & Interferometry Perspective

Optical designers sometimes treat mirrors as simple parts, yet in Optical Metrology & Interferometry the mirror decides beam direction, loss budget and even image…

Optical designers sometimes treat mirrors as simple parts, yet in Optical Metrology & Interferometry the mirror decides beam direction, loss budget and even image contrast. The Protected Gold Mirror is a quietly critical component whose details repay careful attention.

Think of the Protected Gold Mirror as a precisely made silicon, copper or glass plate whose working surface is a protected gold. The result is 98%+ in the IR reflection across 700 nm to 10.6 µm, which is exactly what most Optical Metrology & Interferometry builders are looking for.

The working principle is the law of reflection applied to a coated plane. Mount the Protected Gold Mirror at 45° and a beam turns 90°; stack several and you fold a long path into a short box. That simplicity is why mirrors remain the fastest way to route light in Optical Metrology & Interferometry.

The protected gold is where performance is won or lost. Deposited by vacuum processes, it is tuned so the reflected wave adds constructively across 700 nm to 10.6 µm, reaching 98%+ in the IR. Getting the layer thickness right is a precision task: a few nanometers off and the reflectivity curve shifts.

A Protected Gold Mirror starts as a silicon, copper or glass blank. We hold it to λ/4 flatness and 40-20 surface quality, then apply the protected gold. The substrate never sees the beam directly, but its figure sets the limit on how straight the reflected wavefront stays.

A practical Protected Gold Mirror datasheet reads: silicon, copper or glass substrate, λ/4 flatness, 40-20 quality, 0.5–6 mm thick, 98%+ in the IR over 700 nm to 10.6 µm. Those five lines settle most design reviews for Optical Metrology & Interferometry. See the standard size list for what we stock and what we cut to order.

Where comparing wavefronts to a reference with sub-wavelength accuracy, a Protected Gold Mirror earns its place by doing one job reliably: turning the beam without adding noise. In Optical Metrology & Interferometry 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.

Behind the performance

What reads on a datasheet as "98%+ in the IR over 700 nm to 10.6 µm" is really the outcome of interference. The protected gold on a silicon, copper or glass base is built layer by layer so reflected waves reinforce. Flatness λ/4 then keeps that wavefront from bending. The physics is old; the discipline to repeat it is the hard part.

For Optical Metrology & Interferometry, do not over-specify. Choose the protected gold that covers 700 nm to 10.6 µm at the angle you use, keep flatness at λ/4 unless the wavefront demands more, and you will have a Protected Gold Mirror that is both capable and economical.

Treat the protected gold as the asset it is. In Optical Metrology & Interferometry service, a Protected Gold Mirror that is cleaned rarely and handled by the edge outlasts one that is wiped often. Less touching, more performance.

At JYOPTO we make Protected Gold Mirror parts by cutting silicon, copper or glass with laser accuracy of ±0.01 mm, then applying the protected gold under vacuum. Standard blanks run 0.5–6 mm thick, edges are smoothed for safe handling, and every shipped mirror meets λ/4 flatness with a 40-20 surface — the same disciplines we apply across our optical glass, vacuum-coating and precision cold-processing lines since 2020.

The Protected Gold Mirror is not exclusive to Optical Metrology & Interferometry. Universities, service centers and R&D groups use it wherever a beam must turn, which makes a flexible, customizable part a quiet workhorse across the optics world.

Treat the protected gold as the asset it is. In Optical Metrology & Interferometry service, a Protected Gold Mirror that is cleaned rarely and handled by the edge outlasts one that is wiped often. Less touching, more performance.

At its core, the Protected Gold Mirror is a silicon, copper or glass element carrying a protected gold. That stack is engineered to return incident light efficiently over 700 nm to 10.6 µm, giving designers a predictable, low-loss way to steer a beam where they need it.

One term worth knowing

"Reflectivity" on a Protected Gold Mirror is the fraction of incident light returned by the protected gold. Quoting 98%+ in the IR without the band (700 nm to 10.6 µm) is meaningless, because the same coating can be excellent at one wavelength and poor at another — always pair the number with the range.

At JYOPTO we make Protected Gold Mirror parts by cutting silicon, copper or glass with laser accuracy of ±0.01 mm, then applying the protected gold under vacuum. Standard blanks run 0.5–6 mm thick, edges are smoothed for safe handling, and every shipped mirror meets λ/4 flatness with a 40-20 surface — the same disciplines we apply across our optical glass, vacuum-coating and precision cold-processing lines since 2020.

When light meets the Protected Gold 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 Optical Metrology & Interferometry setups.

Beyond Optical Metrology & Interferometry, the same Protected Gold Mirror shows up in laboratories, teaching setups and OEM builds where comparing wavefronts to a reference with sub-wavelength accuracy. Its value is generality: one well-made part serves many breadboards, which is why stocking a few standard sizes pays off.

Quality control

Every Protected Gold Mirror is measured, not just sampled. Flatness against a reference, scratch-dig against 40-20, and a reflectance spot-check at 700 nm to 10.6 µm confirm the protected gold performed as designed. Documented results matter most for Optical Metrology & Interferometry, where one bad part can stall a whole instrument.

Behind the coating sits the silicon, copper or glass substrate. Its job is mechanical: hold flatness, survive cutting and mounting, and stay stable with temperature. For many Optical Metrology & Interferometry uses, silicon, copper or glass hits the right balance of cost, flatness (λ/4) and workability.

A word on installation

When fitting a Protected Gold Mirror into Optical Metrology & Interferometry hardware, handle it by the edges, seat it against a clean flat, and torque gently. Stress on the silicon, copper or glass shifts the figure and costs you the very flatness (λ/4) you paid for.

Durability is part of the spec, not an afterthought. For Optical Metrology & Interferometry the Protected Gold Mirror should survive shipping, installation and the occasional wipe. The protective overcoat on the protected gold is what lets it do that without losing 98%+ in the IR over time.

A Protected Gold Mirror is tougher than it looks but softer than you think. Fingerprints on the protected gold are the usual cause of field failures, so edge-handling and capped storage pay off. A little discipline keeps 98%+ in the IR where it belongs.

Wrapping up

A Protected Gold Mirror is a small part with an outsized effect on Optical Metrology & Interferometry. Get the protected gold, silicon, copper or 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.