01Precision optics & quartz
Where the drawing
is the whole contract.
Windows, lenses, prisms and mirrors made to an ISO 10110 print — read line by line, quoted against the tolerance you actually wrote, and verified on the lot with an interferogram and a transmission scan. This is the category we know deepest.
01Materials
Substrate choice decides the price
More than any tolerance on the print. The same window in N-BK7 and in UV fused silica differs by 2–4×; in CaF₂ by 8–15×. Getting the substrate right is where a quotation is won or quietly overspent.
Table 1 · Optical substrate properties, typical values
| Material | Transmission µm | nd | Vd | CTE 10⁻⁶/K | Knoop kg/mm² | Chosen for |
|---|---|---|---|---|---|---|
| N-BK7 | 0.35–2.0 | 1.517 | 64.2 | 7.1 | 610 | The default for visible and near-IR; cheapest good polish |
| UV fused silica | 0.185–2.5 | 1.458 | 67.8 | 0.55 | 480 | Deep UV, excimer lasers, anything thermally loaded |
| CaF₂ | 0.13–10 | 1.434 | 95.1 | 18.9 | 158 | UV to mid-IR in one part; spectroscopy |
| Sapphire | 0.15–5.5 | 1.768 | 72.2 | 5.0 | 2,000 | Scratch resistance, harsh environments, high pressure |
| ZnSe | 0.5–20 | 2.403 | — | 7.1 | 120 | CO₂ laser optics, thermal imaging |
| Germanium | 2.0–14 | 4.02 | — | 6.1 | 780 | LWIR imaging; high index means fewer elements |
| Silicon | 1.2–7.0 | 3.42 | — | 2.6 | 1,150 | MWIR, weight-sensitive IR systems |
| MgF₂ | 0.11–7.0 | 1.380 | 95.0 | 13.7 | 415 | Deep-UV windows, durable MgF₂ coatings |
Scroll the table sideways for all columns →
One trap worth naming. Fused silica is sold in grades that differ in OH content — and the grade decides whether 2.7 µm is usable. If your application runs past 2.2 µm, say so in the print; otherwise you will receive UV-grade and lose the band you needed.
02Tolerances
Three bands, three prices
Most prints arrive tighter than the application needs. The jump from λ/4 to λ/10 roughly doubles the polishing time and can double the price — so the first thing we check is whether the number on the drawing was chosen or inherited.
Table 2 · Fabrication tolerance bands for plano and spherical optics
| Attribute | Standard catalogue grade | Precision instrument grade | High laser / imaging |
|---|---|---|---|
| Diameter tolerance | +0.00 / −0.10 mm | ±0.025 mm | ±0.010 mm |
| Thickness tolerance | ±0.10 mm | ±0.025 mm | ±0.010 mm |
| Surface figure @633 nm | λ/4 | λ/10 | λ/20 |
| Surface quality scratch–dig | 60-40 | 40-20 | 20-10 · 10-5 |
| Parallelism | 1 arcmin | 10 arcsec | 1 arcsec |
| Angle tolerance prisms | ±3 arcmin | ±30 arcsec | ±5 arcsec |
| Centration lenses | 3 arcmin | 1 arcmin | 30 arcsec |
| Roughness Ra | ≤2 nm | ≤1 nm | ≤0.5 nm |
| Edge | 0.2–0.5 mm bevel | 0.2–0.3 mm bevel | 0.1–0.2 mm, chip-free |
Scroll the table sideways for all columns →
Scratch–dig is two numbers, not one. Under MIL-PRF-13830B a 40-20 part permits scratches up to 40 and digs up to 20 by the standard's visual comparison. Under ISO 10110 the same part is written 5/40×0.16 — different notation, close intent. We confirm which standard the drawing is in before quoting, because a supplier reading the wrong one will pass a part you reject.
03Quartz glass
JGS1, JGS2 or JGS3
Chinese quartz is usually quoted by these three designations rather than by brand. They are not grades of the same material — they are different OH contents, and that single difference decides the usable wavelength band.
Table 3 · Fused quartz designations and their Western equivalents
| Designation | Range µm | OH content | Bubble / stripe | Equivalent | Used for |
|---|---|---|---|---|---|
| JGS1 | 0.185–2.5 | high OH ~1,000 ppm | 0–1 class | Suprasil 1 · Corning 7940 | Deep UV, excimer optics, UV spectroscopy |
| JGS2 | 0.25–2.5 | high OH ~1,000 ppm | 1–2 class | Suprasil 2 · Corning 7980 (vis) | Visible windows, general instrument optics |
| JGS3 | 0.26–2.8 | low OH <10 ppm | 1–2 class | Infrasil · IR-grade silica | Near-IR through 2.8 µm, no 2.7 µm OH band |
| Doped / special | to 3.5 | OH-free | on request | — | IR windows, high-power laser substrates |
Scroll the table sideways for all columns →
Ask for the OH figure, not the designation. We have seen JGS2 quoted for a 2.6 µm application where only JGS3 works — the designation was right for the supplier's stock, wrong for the job. A number in ppm settles it in one line.
Coating specifications we write into the order
- BBAR
- R < 1% average, 400–700 nm or per your band; angle of incidence stated
- V-coat
- R < 0.25% at a single design wavelength, narrow band
- HR dielectric
- R > 99.5% over a defined band; LIDT measured, not extrapolated
- Protected Al
- R 88–92% visible; acceptable where cost dominates and humidity is controlled
- Protected Ag
- R 97–98% visible to near-IR; overcoat mandatory for tarnish resistance
- Durability
- Adhesion and abrasion per MIL-C-48497A, plus humidity and temperature cycling
04Qualification
How we qualify a polisher
Optics is the category where the certificate matters most and is checked least. Six things we look at before the first paid order — and again on the lot that ships.
Which standard is the print in
ISO 10110, MIL-PRF-13830B or an in-house format. The three use different notation for the same intent, and a shop that reads the wrong one will confidently pass a part you reject.
Figure measured, not claimed
An interferogram on the actual part, with the wavelength and the tested aperture stated. A λ/10 claim from a 25 mm test aperture says nothing about a 100 mm window.
Scratch–dig under the right light
Dark-field inspection against the standard's comparison plates, with the inspector named. Scratch–dig is a visual judgement and it is the first thing that gets generous when a lot is late.
Coating curve on the lot
A spectrophotometer scan of the coated part, not the design curve from the coating software. Edge fall-off and centre-to-edge uniformity are where a coating quietly fails.
Substrate certificate
Glass grade, melt number and homogeneity from the glass supplier — matched to the parts. Uncertified substrate is how a "fused silica" window turns out to be a cheaper borosilicate with a good polish.
Cleaning and packing
Class 100 cleaning, lint-free tissue, part-specific carriers. A perfect surface packed against a foam insert arrives with the insert's texture printed on it.
05Where it goes wrong
Three failures we see most often
Overspecified figure
λ/10 written where λ/4 would image fine. It is the single easiest way to double a quotation — and because the part still passes, nobody ever discovers the money was unnecessary.
Scratch–dig by eye, both sides
A 20-10 part inspected under office light is a 40-20 part by the time it reaches you. Specify the inspection light source and the standard revision, and require the reject rate to be reported.
Coating on the wrong substrate
A coating design is tied to the substrate's index. Swap N-BK7 for fused silica without re-optimising and the curve shifts — the part passes visual inspection and misses the reflectance spec by a percent.
Other categories
Often quoted alongside
Precision ceramics & machined parts
Alumina, zirconia and SiC fixtures that hold the optic in place.
View category 02 · CrystalsPiezoelectric & scintillation crystals
Optical-grade LiNbO₃ and sapphire, plus scintillators.
View category All fiveWafers, handling & the rest
Silicon, SiC and sapphire substrates, plus PFA carriers.
Back to overviewSend the print. We will quote the tolerance you wrote.
If a number on the drawing is costing you money without buying performance, we will say so — in writing, before you place the order, with the price at the looser grade next to it.