Glass Witness Samples | Sydor Optics

Custom Witness Sample Fabrication

Best practices suggest that when coating or setting up an optical component, it’s best to use a witness sample, also called a “test piece,” to ensure that the actual part will match your specific coating specifications and your application.

Sydor Optics also offers witness samples for the measurement of coating stresses on substrates. The size and thickness of a witness sample will typically match your finished product.

Test samples available before the commitment of a high-volume run

Available Material Types

Based upon customer demand, Sydor Optics offers Witness Samples made from the following optical substrate materials. Of course, if you don’t see a material you need, please contact a Sales Engineer, who will gladly discuss additional options that may be available.

Color Filter Glass
Colored filter glass is available in a range of spectral characteristics each suited to unique transmission and absorption properties of various wavelengths of light.
- Bandpass
- UV Bandpass
- Longpass
- Shortpass
- Multiband
- Neutral Density
- Color Compensating – Cyan
- Blue
- Green
- Heat Absorbing
- Infrared Transmitting
- Light Balancing – Amber
- Light Balancing – Blue
- UV Transmitting / VIS Absorbing
- Sharp Cut – Colorless
- Sharp Cut – Orange
- Sharp Cut – Red
- Sharp Cut – Yellow
- UV Transmitting
- UV Sharp Cut
- Color Compensating – Blue
- Light Balancing
  - Isuzu ILA-400
  - Isuzu ILB-90
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Crystal
Optical crystals are glass-like materials grown from high-purity raw materials. The most common crystals include calcium fluoride—effective for UV-spectrum applications—and magnesium fluoride, which is useful for mid-wave IR applications.
- Calcium Fluoride (CaF2)
- Magnesium Fluoride (MgF2)
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Display Glass
Borosilicate glass, also called display glass, offers a combination of excellent light transmission and impressive technical properties. Made of silicon oxide and boron oxide, display glass is easily laser- or CNC-machined. In addition to having excellent chemical resistance, the material possesses a low coefficient of thermal expansion, meaning that it can resist high temperatures without cracking.
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Fused Quartz
Fused Quartz is made using high quality, natural quartz powders with several fusion methods. Quartz material is stronger than glass, can be used at high temperatures (<1050°C) and has a high average transmission of over 80% from 260nm to 2500nm. The various qualities of fused quartz allow for use in a wide range of applications from semiconductor applications to lower precision window applications in hostile environments.
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Fused Silica
Fused silica is a transparent glass formed by melting and cooling pure silica sand. Unlike most other glasses, fused silica does not contain any additives. It is an amorphous solid with a purity that gives it excellent optical transmission.
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IR Materials
Infrared materials produce good transmission in the infrared (IR) spectrum, which spans 0.75 μm to 15µm. Infrared materials are commonly selected for their transmission properties in the NIR (0.75µm – 1µm), SWIR (1µm – 2.7µm), MWIR (3µm – 5µm) or LWIR (8µm – 12µm) spectral sub-regions. The most common IR materials are silicon, germanium, sapphire, zinc sulfide, and zinc selenide.
- Germanium
- Sapphire
  - Gavish Sapphire
  - Ohara Sapphire
- Silica
  - Corning HPFS 7979 (UV & IR Grades)
- Silicon
- Zinc Sulfide
- Zinc Selenide
  - Hellma CVD Zinc Selenide
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Optical Glass
Optical glass is known for its high transmission, low dispersion, and homogenous refraction indices. These properties result from the continuous melting process and subsequent finishing methods used to create optical glass. This material is categorized into either flint glass or crown glass. Flint glass has an Abbe number < 55 and generally < 50. Flint glass is denser due to the inclusion of various metal oxides and exhibits strong chromatic dispersion. Crown glass has an Abbe number> 50 and generally > 55. Crown glass is typically less dense resulting from higher usage of alkali metals and exhibits low chromatic dispersion.
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Witness Sample Manufacturing Limits

Specifications	Measurements
Diameter	customer specified (typically 25mm – 50mm)
Thickness	customer specified (typically 1mm)
Thickness Tolerance	± 0.01mm
Cosmetics (MIL-PRF-13830B)	60-40 to 20-10
Surface Roughness	≥ 5 Ǻ rms
Reflected Wavefront Error (RWE) – before coating	≥ 1/10 wave over clear aperture
Transmitted Wavefront Error (TWE) – before coating	≥ 1/10 wave over clear aperture
Clear Aperture	≤ 95%