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The Photonics Spotlight

Distant Healing of Lasers

Dr. Rüdiger Paschotta

Ref.: encyclopedia articles on laser design, laser development

When someone has a severe problem with his laser, e.g. a prototype device exhibiting excessive laser noise, alignment sensitivity, or beam distortions, it is often hard for him to believe that I can solve the problem without going into that lab in order to inspect and modify the laser. It would seem like a form of distant healing, and technical staff tends to be somewhat skeptical about such things.

It can be instructive to consider how difficult it is to diagnose a problem simply by looking at the laser setup. I might verify that the problem – e.g. excessive noise – really exists, and might see some details which give me some hints (as they also do when the customer sends me some data), but how could I see the cause of the troublesome behavior? In most cases, the cause of such problems is not visible, and doesn't become apparent by touching the device. If it is the alignment sensitivity, for example, I trust that I wouldn't find a loose mirror mount, since my customers are sufficiently intelligent to find out such things themselves.

Obviously, I anyway have to use a different approach. The key is in many cases the laser design, and as a part of that it is frequently the design of the laser resonator. What I need then is a document describing the used optical components (e.g. laser mirrors and their radius of curvature) and their arrangement (including the spacing). I may then find out e.g. that the resonator is operated too close to some critical edge of a stability zone, or that the beam radius in the laser crystal is not appropriate, or that some asymmetry in the thermal lens can cause trouble. The analysis is most efficiently done at the desk in my office (rather than in the customer's lab), and the solution comes as a well founded recommendation – e.g. stating why and how to modify the resonator. That will be part of the consulting report, as sent out via e-mail. (Sometimes this comes faster than I could appear personally to see the laser.) And when my customer has fixed the problem based on my recommendation, there is not only a working laser, but also a customer knowing what to avoid next time.

So there is nothing wrong with distant healing – often enough, it is simply most efficient, when compared with other methods of healing (e.g. healing hands). However, it should not be overlooked that healing with whatever technique is often less efficient than prophylaxis, and this holds for laser issues at least as much as for the human health. If the laser design is properly worked out before any tedious experiments are done, one saves all the time for diagnosing and solving certain problems. The essence for efficiency (in terms of time and money) is to properly organize the laser development process. Unfortunately, people in industry (much like researchers, I am afraid) too often try the “quick and dirty” solution, only to find out that it is dirty indeed, but for sure not quick. Some recommended reading:

P.S. In the case that you expected to read something about distant healing with lasers, I would recommend to look out for a less sophisticated technology.

This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page, because its location is permanent. See also the Encyclopedia of Laser Physics and Technology.

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