Production methods

The standard coating technique is physical vapor deposition (PVD). In a high vacuum chamber, thin layers are applied to the substrate surface. The most used deposition processes are Thermal Evaporation (TE, using evaporation boats), Electron Beam Evaporation (EBE), Ion Assisted Deposition (IAD) and sputtering, like Ion Beam Sputtering (IBS) and Magnetron Sputtering (MS).

Besides PVD, Chemical Vapor Deposition (CVD) is also common. Here LASEROPTIK uses Atomic Layer Deposition (ALD), which allows extreme film conformality and thickness control at the sub-nano level, even on 3D-optics.

https://www.laseroptik.com/en/coating-guide/production-methods/overview-coating-techniques

With Evaporation, the heated coating material evaporates and condenses as a thin layer on the substrates. The most common methods here are Thermal Evaporation (TE) and Electron Beam Evaporation (EBE). With Ion Assisted Deposition (IAD) and Ion Plating (IP), the growing layers are additionally compacted by ion bombardment.

Sputtering techniques, like Ion Beam Sputtering (IBS) and Magnetron Sputtering (MS), use very high-energy ions to knock atoms out of a solid. Due to the high impulse transfer, they deposit on the substrate surface with a high packing density.

Chemical Vapor Deposition (CVD) does not evaporate or sputter solids. The desired layers are achieved by the inlet of reaction and carrier gases. LASEROPTIK uses Atomic Layer Deposition (ALD) here, where the coating grows in atomic layer after atomic layer.

You can find a more precise description of the coating techniques used at LASEROPTIK here:

https://www.laseroptik.com/en/coating-guide/production-methods

Electron Beam Evaporation (EBE) and Thermal Evaporation (TE) have a very good cost-performance ratio. Due to the columnar structure the layers are not so dense and therefore can show a thermal drift.

Ion Beam Sputtering (IBS) has the highest precision and should be used especially for complex coatings, lowest losses or challenging dispersive coatings. The lower deposition rate increases the run price, compared to EBE or TE.

Magnetron Sputtering (MS) produces coatings as dense as IBS and some of LASEROPTIK’s coatings are certified by ESA. Due to the manufacturing conditions, MS coatings usually show slightly more stress and scattering than IBS.

Ion Assisted Deposition (IAD) is something in between EBE and Sputtering.

Atomic Layer Deposition (ALD) can coat 3D-optics with extreme film conformity. Due to the very low deposition rate, coatings are quite expensive.

You can find a table with a precise comparison of the coating techniques used at LASEROPTIK here: https://www.laseroptik.com/en/coating-guide/production-methods/comparison-of-coating-techniques

In VIS-NIR you normally will get the lowest absorption with IBS coatings. For shorter wavelengths it depends on the application and the substrate material used. Therefore, you must choose the coating technique wisely here.

There is no general statement about which coating technique has the highest LIDT, as too many parameters influence it, e.g. pulse duration, repetition rate, beam size, substrate material,...

In addition, the deposition materials must be specially selected depending on the application. Normally the highest reflectance cannot be achieved together with the highest LIDT.

https://www.laseroptik.com/en/coating-guide/thin-film-basics/hr-standards

As a rough rule, the highest LIDT will usually be obtained:

• for cw applications with sputtered layers (MS or IBS)
• for ultrashort pulses (fs/ps) with IBS
• below 200 nm with fluoride layers (TE)

Ion Beam Sputtering (IBS) is the most advanced deposition technology for the most critical demands on laser optics, due to highest precision in film growth and an amorphous, almost defect free microstructure. For this reason, LASEROPTIK is constantly increasing its capacities in this area and is the largest supplier in Europe with 18 IBS systems currently running.

With the accuracy of LASEROPTIK’s broadband monitoring systems, even fractional parts of a monolayer can be detected.

But there are limitations, especially in the VUV/UV-range, where the typical IBS coating materials absorb. For wavelengths below 190 nm you should choose fluorides as substrate and coating materials. Normally Thermal Evaporation (TE) is the only option here, LASEROPTIK can offer this with specially converted EBE coating machines.

And there are other reasons for choosing other coating techniques, e.g. limitations in substrate thickness, LIDT for ns-pulses, and run capacity.

Here you can find a comparison of the preferences for all coating techniques LASEROPTIK can offer: https://www.laseroptik.com/en/coating-guide/production-methods/comparison-of-coating-techniques

The price of a coating run depends on many factors, especially the coating time, i.e. the deposition rates. Compared to EBE, IBS has much lower rates and is therefore usually more expensive. However, due to the higher process control with IBS, there are no additional costs for test coatings, which would be necessary for difficult coatings with EBE, and the price disadvantage can be cancelled out.

Of course, the total price for a set of optics also depends on how many substrates can be coated together in one run. Standard IBS systems have the greatest limitation, with a maximum coatable area of Ø 30 cm. However, the run capacity for typical substrate sizes of 1/2" and 1" is the same as with EBE.