Laser Applications Newsletter
15 September 1997
Laser Kinetics Inc.
Mtn. View, CA 94041
Issue 1, Vol. 1



INTRODUCTION

Welcome to the first Laser Kinetics on-line newsletter. Through our web site at and e-mail many of you have requested current information on laser processing. We would like the format and content of this publication to evolve to meet the needs of our customers, so please feel free to e-mail us at with any questions, announcements and comments you would like to see in future mailings. Of course, if you do not wish to receive future mailings, send the message "unsubscribe" to NEWS@LASERK.COM

As I noted, this is our first newsletter. I don't know if these things are supposed to have volume numbers or not. Since it's electronic, it may be more appropriate to give it a version number like Wired magazine: Laser Burns 1.01

In these newsletters, we will provide information about laser processes, comments about new developments, and announcements of upcoming events in the laser field, especially if we have something to do with them. Publication will initially be at random dates; there may be a schedule in the future.


LASER PROCESSING TIPS

Polarization effects in laser cutting

The polarization of a laser beam has a strong effect on its interaction with materials. The plane of polarization of a light wave is, in effect, the direction that it is vibrating. Many, but not all, carbon dioxide lasers have a polarized output. High power Nd:YAG lasers are usually unpolarized. If you try to cut metal with a polarized beam, you will find that it cuts very well in the direction of the polarization and very poorly at right angles to it. This gets you in a lot of trouble if you're doing contour cutting.

Carbon dioxide laser systems designed for cutting usually have optical components that take the linearly polarized beam from the laser and convert it to a circularly polarized beam. In circular polarization, the direction of polarization rotates 360 degrees every wavelength. For a CO2 laser, that means the polarization makes a full rotation in 35 femtoseconds, or not a very long time. For all practical purposes, a circularly polarized beam behaves as if it were unpolarized. This lets the laser cut equally well in all directions.

You have to be careful when replacing mirrors on systems with circular polarization. The polarizing unit itself (sometimes called an ECQ) has a special mirror called a 1/4 wave plate. This mirror, when properly aligned with a linearly polarized beam, is what converts it to circular polarization. If the polarizing unit has more than one mirror, it is not obvious which is the 1/4 wave plate, or if both of them are 1/8 wave plates. If the wrong mirror type is used as a replacement, cutting performance will suffer.

Mirrors after the polarizer are also critical. All mirrors have phase shift, which alters circular polarization. It is desirable to have a phase shift no greater than 6 degrees for mirrors used with circularly polarized light. Greater phase shifts can cause cutting problems.

The usual diagnostic for polarization is to cut a circle in the thickest steel the machine will handle. Polarization will manifest itself by making the cut unsquare to the plane of the material. If you roll the circular slug on a flat table, it will wobble from side to side if the polarization is not circular.

ENDNOTE
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