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MAY 2021 I DESIGN007 MAGAZINE 91 For example, in environmental chamber tri- als simulating highly condensing conditions, while a urethane resin potted assembly gave the highest overall values in terms of circuit protection—and showed the least change dur- ing condensing events—the very large differ- ence in thickness between it and a two-part conformal coating didn't show a large increase in performance. Indeed, the two-part coating achieved much the same results as the potting compound at one-tenth the thickness. Despite these advances in conformal coat- ing chemistries, potting and encapsulation resins will always offer the highest level of protection for PCBs, whether used to protect against mechanical shock and vibration, ther- mal cycling, chemical attack, or the presence of high voltages where maximum dielectric strength is needed to avoid damaging dis- charges and leakage currents. e trade-offs are added weight, loss of rework capability, longer processing times, and high cure tem- peratures. If you do experience problems choosing between these methods of circuit protection, remember, there are experts out there to help. And it is always worthwhile taking the trouble to test alternative methods of protection, pref- erably at the prototype stage, before you make your final choice; the experts are ready to help you with this task as well. DESIGN007 Phil Kinner is the global busi- ness and technical director of conformal coatings at Electro- lube. To read past columns or contact Kinner, click here. Down- load your free copy of Electrol- ube's book, The Printed Circuit Assembler's Guide to… Conformal Coatings for Harsh Environments, and watch the micro webinar series "Coatings Uncoated!" New research shows how to measure the super- short bursts of high-frequency light emitted from free electron lasers (FELs). By using the light- induced ionization itself to create a femtosecond optical shutter, the technique encodes the electric field of the FEL pulse in a visible light pulse so that it can be measured with a standard, slow, visible-light camera. "This work has the potential to lead to a new online diagnostic for FELs, where the exact pulse shape of each light pulse can be determined. That information can help both the end-user and the accelerator scientists," said Pamela Bowlan, Los Alamos National Laboratory's lead researcher on the project. The paper was published April 12, 2021 in Optica. "This work also paves the way for mea- suring x-ray pulses or femtosecond time-resolved x-ray images." Free electron lasers, which are driven by kilome- ter-long linear accelerators, emit bursts of short- wavelength light lasting one quadrillionth of a second. As a result, they can act as strobe lights for viewing the fastest events in nature—atomic or molecular motion—and therefore promise to revolutionize our understanding of almost any kind of matter. Squeezing all of the energy of a continuous laser into short pulses means that femtosecond laser pulses are extremely bright and have the ability to modify a material's absorption or refraction, creat- ing effectively instantaneous "optical shutters." The researchers showed that ionization itself can be used as a "femtosecond optical shutter" for measuring extreme ultraviolet laser pulses at 31 nanometers. (Source: Los Alamos National Laboratory) New Method Measures Super-Fast, Free Electron Laser Pulses

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