Tolerances for Substrates

From mini to maxi sizesLASEROPTIK has a wide selection of sizes and materials in stock but can also provide nearly every custom optic manufactured to your individual needs.

For a quotation we need to know at least the following information:
• material
• quantity and size
• for curved surfaces: radii of curvature
• used aperture

If we do not get any other information we will choose standard quality properties and standard tolerances.

Please note: the quality of the substrate has to be chosen with the specifications of the coating in mind. For example low loss mirrors need  to have substrate surfaces with a low micro-roughness. You can of course use super poli­shed optics for a standard mirror, but that might be a waste of money. Our standard polishing quality is P4.

It is common to accept tolerances for substrate size but also for variations of surface form and surface imperfections. Nevertheless some applications require more precise specifications.

Here you can find a description of how to specify substrates according to DIN ISO 10110:

Code number 0
Material imperfections: Stress birefringence (DIN ISO 10110-2)
• specified as 0/A
• where A is the maximum allowable stress birefringence in nanometers per centimeter of optical path length, e.g. 0/5

Code number 1
Material imperfections: Bubbles and inclu­si­ons (DIN ISO 10110-3)
• specified as 1/N x A
• where N is the number of bubbles and inclusions with a maximum allowable size A, e.g. 1/3 x 0.010

Code number 2
Material imperfections: Inhomogeneity and striae (DIN ISO 10110-4)
• specified as 2/A;B
• where A denotes the inhomogeneity class and B denotes the striae class, e.g. 2/5;5

Code number 3
Surface form tolerances (DIN ISO 10110-5)
• specified as 3/A (B/C)
• where A is the maximum permissible power deviation (≈ peak to valley (PV) of the best-fit-sphere), B is the maximum permissible PV of the resulting surface after subtracting the best-fit-sphere (= irregularity) and C is the maximum permissible PV of the best fit asphericity of the irregularity (= rotationally invariant irregularity).
Therefore C is a subset from B.
• please see DIN ISO 14999 for more detailed information.

Usually, the values are tolerated in fringes, but nanometers are possible as well.

fringesnanometer
2 546.07 nm
1 273.04 nm
0.5 136.52 nm
0.4 126.60 nm
0.2 54.61 nm
0.1 27.30 nm

Example
3/0.5 (0.2/0.1) = 3/136.5 nm (54.6 nm/27.3 nm)

Commonly the surface form tolerance is stated as flatness and can be roughly converted into values of the measuring wavelength λ, as shown in the following table. Please note that the achievable flatness strongly depends on the diameter-thickness-ratio of the substrate.

   3/0.1 (0.1)     3/0.2 (0.2)     3/0.5 (0.5)     3/1 (1)     3/2 (2)   
      λ/20               λ/10                λ/4                λ/2            λ 

Code number 4
Centring tolerances (DIN ISO 10110-6)
• specified as 4/σ
• where σ denotes the maximum permissible wedge angle by spherical surfaces, e.g. 4/3’

Code number 5
Surface imperfection tolerances (DIN ISO 10110-7)
• specified as 5/N x A
• where N is the number of allowed surface imperfections with maximum size A, e.g. 5/3 x 0.025
• other codes represent additional errors: C stands for coating imperfections, L for scratches with any length and E for chips
• a possible complete nomenclature would be 5/3 x 0.025; C3 x 0.025; L1 x 0.001; E 0.2
• please see DIN ISO 14997 for more detailed information

Code number 6
Laser irradiation damage threshold (DIN ISO 10110-17)
• specified as 6/
• More information regarding the LIDT click here.

Code number 13
Wavefront deformation tolerance (DIN ISO 10110-14)
• specified as 13/A (B/C)
• where A is the maximum permissible sagitta deviation (single pass), B is the maximum permissible irregularity (single pass) and C is the permissible rotationally invariant irregularity (single pass), e.g. 13/0.2 (0.2/0.1)
• compare with the additional information given for 3/A (B/C)
• please see DIN ISO 14999 for more detailed information.

The above explanations of DIN ISO 10110 are simplified. For more information please see the complete text of DIN ISO 10110.

Another way to specify substrates is to use the MIL-norms. A comparison between MIL and DIN ISO is very difficult and reveals that the  DIN ISO 10110 provides finer levels for decisi­ons.

For the standard surface quality of our sub­stra­tes we can give you the following values:

 
clear aperture
up to Ø		according to DIN ISO 10110-7
surface imperfections		according to MIL-0-13830A
Scratch/Dig1)
12.7 mm 5/3 x 0.025; L1 x 0.001 10 / 5
25 mm 5/3 x 0.025; L1 x 0.001 10 / 5
50 mm 5/3 x 0.025; L1 x 0.001 10 / 5
75 mm 5/3 x 0.040; L1 x 0.001 20 / 10
100 mm 5/3 x 0.063; L2 x 0.001 20 / 10

1) Please note: The scratch/dig information in accordance with MIL-13830 shall apply for a maximum inspection area of Ø 20 mm.

For special customer-owned substrates (e.g. crys­tals) we additionally need to know the following properties:
• maximum temperature we can use while coating
• thermal expansion coefficient
• refractive index
• incompatibility e.g. with certain cleaning sol­­vents

LASEROPTIK has decades of experiences in coa­ting on all kind of substrates and a large data base, but we gratefully accept any additional information about the characteristics of your substrates.

For choosing the correct substrate size it might be useful to think about the possible aperture and about the holders used for the coating process:
• If not described otherwise we use holders with rims (normally covering about 2% of the dia­meter, minimum 0.5 mm) which will remain uncoated.
• If the coating has to be rimless, small defects caused by the clamp holder and overspray can occur on the sides of the substrates.

We do have over 16,000 substrate holders avail­able and can work with nearly all sizes. Of course we will find a special holder system for your substrates if necessary.

Data sheet

The data sheet for the standards of specification for our uncoated substrate S-00010 according to DIN ISO 10110.

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