When light passes from one medium into another, back reflections occur, which equates to approximately 4% loss for air to glass interfaces. Without anti-reflection coatings, considerable losses would result in optical systems in which light passes through a number of interfaces. After passing through ten interfaces, only 66% of the original output power would reach the end of the system.
Back reflections on lens surfaces not only reduce output power, but can also focus light down to small spots creating high power densities. For laser applications this can be damaging to other surfaces and boundaries such as lens doublets.
LASER COMPONENTS has more than 20 years’ experience in the manufacture of high efficiency coatings and offers optimum coatings for many applications. Assorted AR coatings are discussed as follows:
Single layer AR Coatings
The single layer AR coating is the simplest coating, consisting of a single MgF2 layer of Lambda/2 thickness. Optimum performance is achieved when the refractive index of the coating is nC = sqrt (nSubstrate). This coating is therefore mostly used on materials that have a high refractive index such as sapphire or soft flint glasses such as SF10. You will find a comparison of the effect these coatings have on sapphire and BK7 in the graph above.
V-AR and U-AR Coatings
These coatings consist of several layers. They are optimised for one wavelength or for a small range of wavelengths and have the best performance for BK7 and fused silica glasses. V-AR coatings achieve a residual reflection of < 0.2% per surface at 1064nm and U-AR coatings achieve < 0.1% at an even larger wavelength range. V-AR and U-AR coatings are available from 193nm to 3000nm.
Broadband AR Coatings
Broadband anti-reflection (BBAR) coatings cover the entire wavelength range from 193nm to 1600nm. The table shows the available standard ranges supplied by LASER COMPONENTS. Custom BBAR coatings for other wavebands are offered.
Double AR and Multiple AR Coatings
These coatings are designed for laser fundamental wavelengths and its harmonic, or doubled, wavelength. Examples include 1064nm + 532nm, and 800nm + 400nm. With these coatings residual reflections of < 0.3% at 1064nm and < 0.4% at 532nm can be achieved. LASER COMPONENTS now has a quadruple AR coating capability for all Nd:YAG wavelengths (1064nm, 532nm, 355nm, and 266nm). More information can be found in our new Optics catalogue, email us for your copy.
Special AR Coatings
LASER COMPONENTS also offer custom AR coatings. These coatings are applied to, for example, exotic materials or prisms with incident angles varying from 0° to angles exceeding Brewster’s angle. Contact us for your specific requirements.
| BBAR Type | BBAR-U | BBAR-A | BBAR-B | BBAR-C | BBAR-D | BBAR-E | BBAR-F |
| Wavelength Range | 192-308 | 248-355 | 355-532 | 400-700 | 633-1064 | 800-1315 | 1050-1600 |
| Average Reflectivity at 0° a.o.i. | <1.0% | <0.5% | <0.4% | <0.4% | <0.4% | <0.4% | <0.4% |
