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Optical Coatings Technology Advancement at Laser Components

Date Announced: 26 Jul 2010

A new measurement system for optical broadband monitoring of layer thickness opens the door to innovative products. The following sections summarise new capabilities and growth areas.

Optical Coatings at LASER COMPONENTS
Dielectric coatings have been manufactured in house at LASER COMPONENTS since 1986. The term ‘laser optics’ covers everything from mirrors, lenses, and output couplers, to polarisers used in laser systems. Using new technology and engineered process control, both existing products can be improved and new innovative products manufactured.

Our in-house optics production site has a wide variety of coating technologies. The most common method is known as physical vapour deposition (PVD) or e-beam. In this method, dielectric materials are evaporated using an electron beam in a vacuum. These inexpensive coatings feature very high damage thresholds, particularly with laser pulses in the nanosecond range.

Designed for use with the highest laser power achievable, we have ion-assisted deposition (IAD) coatings available. The coating chamber features a powerful ion source. The condensed layers are exposed to a jet of low-energy ions. The resulting layers are very compact and do not exhibit thermal drift.

Online Measurement of Coating Thickness
The demands made on high-quality coatings in the laser industry are constantly increasing. To meet some of these demands, such as extremely high production precision and batch reproducibility, a broadband monitoring system for the optical in-situ measurement of layer thickness was recently installed in the IAD coater.

In contrast to conventional testing methods, with in-situ monitoring, the thickness of the deposited layer is measured directly on a substrate inside the chamber. A major advantage is that the entire visible optical spectrum is used to monitor the layer thickness.

The combination of ion-assisted coatings with the broadband monitoring of layer thickness leads to advantages when implementing complex coatings. Coatings with improved specifications can be implemented just as easily as new products.

New Product - TFPB Broadband Polarisers
One example is the enhancement of the thin film polariser (TFP), which is used at the Brewster angle of approximately 56°. While the p-polarised portion of the incident light is transmitted and experiences only a slight beam displacement, the s-polarised portion is reflected and experiences a deflection of approximately 112°. The idea is to achieve a high transmission Tp of the p portion and the highest possible extinction ratio Tp/Ts.

a) Low alignment error
New thin-film polarisers were developed with the help of broadband monitoring. The broadband polarisers known as TFPB not only have a better extinction ratio but are also alignment free. This means that they achieve an extinction ratio of more than 300:1 across the entire angular range from 54° to 58°. Even in slightly divergent or focused beams TFPBs can be used without suffering any losses.

b) Precise wavelength selection
There are two different variations available for this product. One possibility is to choose a specific wavelength. The polariser can then be mounted without alignment within a certain angular range. Alternatively, one can forego the extended angular range and instead retain a precise angle of incidence. With this second alternative, the TFPB can then be used for a wavelength range around the central wavelength. At a central wavelength of 532nm, the interval is approximately 20nm. Furthermore, this coating is now also available for an angle of incidence of 45°, which is particularly advantageous for the user during assembly.

New Product - Polarisation Independent Beam Splitters
Another example of a new product is the polarisation independent beam splitter, which has the same degree of reflection for s-pol and p-pol light. Normally the user achieves different degrees of reflection for each polarisation direction; however, with this new technology, polarisation-independent beam splitters are now available at basically any wavelength.

What to Expect in the Future
Even now we are able to offer bandpasses, optical filters, and transmission and reflection gradients according to customer specifications.

The broadband monitoring system makes it possible to manufacture a multitude of other complex coating designs. For example, very steep edges in short and long-pass mirrors can be produced. In dichroic mirrors a transmission of far above 95% can be achieved. The reflection values are over 99%.


Goldlay House,
114 Parkway,
Email: info@lasercomponents.co.uk
Tel: 01245 491 499
Skype: 01245 491 499
Fax: 01245 491 801

E-mail: kcable@lasercomponents.co.uk

Web Site: www.lasercomponents.co.uk

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