Friday, September 17, 2010

Aristotelian Fun with Lasers


Backstory: Well, our laser is broken again. When we were working on it a few days ago, we heard a loud snapping noise from the power amplifier box, and when we shut off the pump lasers, we found damage spots neatly drilled by the laser into both the front and back surfaces of our titanium sapphire (Ti:S) pre-amplifier crystal. Bummer. Thus, today we were asked an important question in our meeting.

Question: Wat caused this problem.

Aristotle's Answer:
Material Cause--The laser beam and the titanium sapphire crystal.
Formal Cause--Brights spots are imposed in the laser beam, which exceeded the damage threshold of Ti:S and so burned a hole.
Efficient Cause--Diffraction and/or focusing of the laser beam through the damage frequency-doubling KTP crystal in one of the Thales Saga pump lasers.
Final Cause--The Thales execs, design engineers, and/or quality control folks were greedy and slothful, so they cut corners and gave us a defective product. The KTP crystals used were of lower damage threshold and smaller size (it's cheaper that way), resulting in the infrared laser's fluence exceeding the damage threshold of the KTP crystal. The result of this is that said crystal was damaged, and the green (frequency doubled) beam was of poor quality. This poor quality resulted in the development of hots spots in the beam, which grew worse when it was focused. Some of these hots spots exceeded the 10 J/cm^2 damage threshold fluence of Ti:S when focused, which therefore damaged the Ti:S crystal. Incidentally, when the first KTP crystal was replaced by a brand-new out-of-the-box KTP crystal loaned to us by some colleagues with the same laser system from a different university, the new crystal lasted all of 5 minutes. Design flaw.

Conclusion: Even in physics, things such as intent and will matter. In this case, one effect of the capital sins of sloth and greed is that our laser is not working right now, and will probably take some time to be fixed. Therefore, morality--at least as manifested in the practice of ethics--can affect scientific research by sheer accident. Moreover, such things as "final cause"--that is, the exercise of one person's will--can have a direct bearing even in the otherwise deterministic realm of experimental research in the physical sciences.