This affects how the distribution of defects

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the size of the spot on the optical surface. This affects how the distribution of defects influences the value and is an important value to specify. It is recommended to keep this value at 0,5 mm or larger to avoid significant spot-size effects on LIDT, but 0,2 mm is the minimum allowable size within the ISO specification Incidence angle Polarization of the laser beam Type of test: 1-on-1, where each spot is exposed to a single pulsed or S-on-1 where each spot is exposed to S pulses Selecting an Optic Based on LIDT and Staying within Budget Calculating the LIDT needed to specify on your component print, or the minimum LIDT value your catalog part should meet, is a relatively simple process. First, calculate the maximum fluence, or intensity, of your laser beam at the location the beam will encounter the optical surface, ensuring to account for your beam profile. Next, verify potential back reflections, or ghost reflections, from other surfaces that exist in the system. Even if these are reflections from anti-reflection coated surfaces, when focused they can be more intense than the original incident beam. The result determines the maximum fluence any optical surface encounters. Figure 2: Typical LIDT tests at 1064 nm show the different fluences used during S-on-1 testing and the resulting damage frequency. In this test the damage threshold for a laser mirror is found to be 7,5 J/cm 2 , with a clear, relatively steep slope. Figure 2 Figure 1: The laser induced damage in optical coatings can cause degradation in performance and often catastrophic fail- ure. The root cause of damage creates various morphologies of damage, and identifying these morphologies is important for coating and process development. Understanding this phenomena is imperative, as over specifying will drive cost and the resultant damage will degrade laser system performance.
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® COPYRIGHT 2018 EDMUND OPTICS, INC. ALL RIGHTS RESERVED EDMUND OPTICS ® | UK: +44 (0)1904 788600 | GERMANY: +49 (0) 6131 5700-0 [email protected] | FRANCE: +33 (0)8 20 20 75 55 Adding a safety factor for potential hotspots or profile and temporal anomalies in your beam is the next important step. The size of this factor depends on the type, stability, and alignment of your laser. Finally, because laser induced damage is statistical in nature, and this probabilistic nature is not included in the ISO LIDT definition, consider an additional safety factor based on the risk tolerance of your applications. Any LIDT value on an optical component larger than the product of the laser fluence and safety factors will meet your requirements; specifying an even higher LIDT will simply add cost.
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  • Fall '19
  • LIDT

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