Coating on special substrates
LASEROPTIK uses dedicated equipment for dielectric coatings on large optics up to 2 m in length (long axis for rectangular shapes) or 1 m in diameter with a superior spectral uniformity over the complete surface and high LIDT values. Approved automated ultrasonic and manual cleaning procedures guarantee an optimum cleanliness even on these large scale geometries. The possible sizes are listed in the table below.
The uniformity of the coatings is a critical factor for applications in industrial lasers, e.g. for laser beam expansion and delivery systems. Coating design, inner architecture of the machine and in-situ process control help to reduce gradient effects to a minimum. The uniformity can also be adapted to the radii of curvature, for example with cylindrical lenses.
For bar-like long substrates, plane or curved, LASEROPTIK can coat laser mirrors that are amongst the largest in the world (up to 2000 mm in length) by using Ion Beam Sputtering (IBS). This method is commonly known for producing the highest quality thin films, but just on small areas. However, by redefining an advanced substrate motion, an unique approach for long optics was found and has been patented. Currently two custom-built machines are working to offer this unique process. A variance in central wavelength of below ±1% can be achieved for optics up to 2000 mm in length. The 8 measured curves below show the excellent uniformity on a large optic (long axis > 1300 mm) which is coated with an IBS broadband AR.
As with long substrates, round optics can be coated by IAD and EBE if the coating requirements are standard. When it comes to complex coating designs and superior spectral performance, IBS coatings offer adequate solutions. LASEROPTIK has commercial coating systems for substrates up to Ø 400 mm and custom-built machines for up to Ø 550 mm in operation, or adequately for rectangular shapes fitting onto the carrier planet.
These specialized machines also allow the use of three or more coating materials, which is important for advanced thin-film design strategies aiming at the highest LIDT. This capability is crucial for very high energy laser research, also known as petawatt and laser fusion projects. Another common use of large round optics is gravitational wave research. The detector’s sensitivity is dependent on the end mirrors’ perfection, i.e. the total losses and Brownian noise have to be reduced to a minimum. IBS is well suited to this task as its low loss coatings are approved by gyroscope applications (see some values here).
In order to support this innovative equipment, a tailored environment of separate cleanrooms with a dedicated inspection metrology, optic cleaning and annealing solutions was built. It is part of a department that specializes in working with large round and rectangular optics, addressing the highest demands for LIDT, losses and spectral performance.
A space-resolved quality inspection is performed on the whole dimension to check for surface defects and spectral properties, including interferometric inspection. Large optics are held in custom-built lifting and handling tools for inspection, transportation and fixing in the coating machine.