Scientists Use High-Quality Optical Coatings to Produce Low-Loss Mirrors

Scientists Use High-Quality Optical Coatings to Produce Low-Loss Mirrors

25 July 2013

Scientists from the University of Vienna and JILA, a joint institute of the University of Colorado at Boulder and the National Institute of Standards and Technology (NIST), have worked together to develop high-quality optical coatings to produce low-loss mirrors, paving the way for the creation of lasers that can be utilized in precision measurement applications.

The team says it designed epitaxial multilayers through a novel substrate-transfer coating procedure to demonstrate low-loss mirrors displaying both extremely low mechanical loss and high optical quality. The technique provides for a significant reduction in coating Brownian noise and has the potential to influence the performance of narrow-linewidth lasers deployed for precision sensing.

In the past 10 years, scientists dealing with precision measurement have been unsuccessful in reducing excessive mechanical damping of the high-reflectivity coatings that comprise the cavity end mirrors applied in optical interferometry and the fluctuations they exhibit, which hampers advancements in precise measurement of time and space. As a result, a technique that can create high-reflectivity mirrors with high mechanical quality was needed. The team of Austrian and US researchers managed to come up with such a technique by combining aspects of semiconductor mirrors seen in surface-emitting lasers and using mechanical loss knowledge obtained from the field of cavity optomechanics to create the crystalline coating technology.

The researchers used a microfabrication process to separate and then bond high-quality single-crystal films onto curved glass substrates to get around previous limitations to using such materials in general optics applications. One of the barriers was the fact that optical surfaces are generally curved, which impedes direct crystal growth techniques. The second obstacle was the amorphous structure that typical optical substrates are made of, which lacks the order need for seeded crystal growth.

The scientists now plan to combine the optical coatings with a single-crystal silicon cavity developed previously to further enhance the technology and improve its stability, achieving another breakthrough in laser technology.