Laser Energy Output Varies Over Course of Treatment

The energy output of aesthetic lasers can fluctuate significantly during treatment, which may explain variances in outcomes seen by providers, say Tim S. Lister, MD, and Mark P. Brewin of the Salisbury Laser Clinic in Salisbury, Wilshire, UK. For their study, “Variations in Laser Energy Outputs Over a Series of Simulated Treatments” (British Journal of Dermatology, November 2014), Lister and Brewin recorded the energy and pulse time data of seven laser systems using a pyroelectric measurement head with an optical diffuser and associated meter. Each laser was used to perform a pattern of eight, 10-minute simulated treatments followed by five-minute delays. The data was recorded directly into a computer for analysis. All devices had been serviced within six months of the experiment.

The authors found that a long-pulsed alexandrite laser operating at 20J had an actual energy output of between 17.3J and 22.6J over the course of treatment with a mean energy pulse of 17.9J. A long-pulsed pulsed dye laser began at 6.4J then fell to 5.1J (a 22% reduction in energy output) by the eighth treatment. Both the Q-switch alexandrite laser and Er:YAG laser also experienced a decrease in energy output during the course of treatment (29% and 13%, respectively).

Conversely, the 1064nm Nd:YAG laser set at 10J revealed an initial drop in energy per pulse followed by a gradual increase (9.6J-11.4J). The energy output of the short-pulsed Q-switch laser and the ruby laser increased significantly in the first few minutes of treatment before plateauing.

In response to these findings, the authors encourage laser operators to be aware of potential variances in energy output, particularly when looking at pre-treatment patch tests and recommended treatment levels. They also note that they have since instituted a single-output energy measurement performed at the beginning and end of each treatment at their facility and encourage other practitioners to integrate their own energy output measures.

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