Improved method for laser damage testing coated optics

Abstract

The damage test procedure for qualifying a coating run of anti-reflection coated optics consists of scanning a pulsed 1064 nm laser over a 1 cm x 1 cm area on a test sample to illuminate approximately 2400 sites. Scans are repeated at 3 J/cm 2 increments until the fluence specification for the optic is reached. In the past, initiation of 1 or more damage sites was classified as a failed coating run, requiring the production optics in the corresponding coating lot be reworked and recoated. Recent laser damage growth tests of 300 repetitive pulses performed on numerous damage sites revealed that all were stable up to 20 J/cm 2 . Therefore the acceptance criteria has been modified to allow a moderate number of damage sites, as long as they are smaller than the allowed dig size and are stable (do not grow). Consequently many coating runs that previously would have been rejected are now accepted, resulting in higher yield, lower cost, and improved delivery schedule. The new test also provides assurance that initiated damage sites are stable during long term operation.

Substrate and coating defect planarization strategies for high-laser-fluence multilayer mirrors

“…The samples were damage tested at Spica Technologies, Inc. (New Hampshire) over a 1 cm 2 area using the raster scanning technique described by Borden [24]. The advantage of this technique is that it samples a large area, improving the probability of irradiating a large range of defect types.…”

Impact of substrate surface scratches on the laser damage resistance of multilayer coatings

“…The coated samples were tested for laser damage resistance by following the damage test protocol given in ref. [7]. Briefly, a 1064 nm, 3 ns laser with a 1 mm Gaussian spot at 1/e 2 is raster scanned in approximately 200 μm steps across the test area of 1 cm 2 , starting at a low fluence and stepping up in 2 or 3 J/cm 2 increments until damage is observed.…”

Testing the Limits

“…Samples were double-blind tested with the same thin film damage setup, testing protocols, and testing area specified by Borden [3] et al in his paper, "Improved method for laser damage testing coated optics," with the resulting laser damage in the coating classified into three categories:…”