# Scanning a "spiral" or a "disc" with a waveform generator

Question asked by sternhagel on Aug 6, 2013
Hi everybody,

I am using a Agilent arbitrary waveform generator (33500 Series) to drive separately two axis of a 2D scanner, that I deflects a laser beam onto a surface, so means I scan with the beam over the surface.

Now I am struggling with the creation of certain scanning patterns, such as the area of a round disc. I am wondering if somebody of you ever used the waveform generator in such a way and if there is some experience in how to create for example the mentioned disc.

I have already  an idea, but I have no idea how to generate that "voltage shape". Later downwards in this mail more about that. First some remarks.

The applied voltage from the waveform generator for the x- and the y-axis of the 2D scanner translates linearly with the tilt angle of the scanner mirror and therefore with the position of the laser beam on the surface.

Now, I like to apply a certain voltage shape to the x- and y-axid of the 2D scanner so that in the end the area in the shape of a disc is scanned.
Unfortunately, there are some requirements which makes things a bit more complicated.

1. The laser is pulsed with a repetition rate of 1 kHz, and I need to keep the distance between the separate pulses on the surface constant. This means that the "speed" with that the laser beam is scanned over the surface needs to be constant at all times.

2. I'd like to scan this pattern with standard wave forms like sine waves.

Of course, I could just calculate the coordinates for each beam spot and go to each position with step wise voltages... this in principle works, but at such high repetition rates like 1 kHz, the mirror cannot follow the steps anymore. A continuous waveform is therefore the only way to do that.

My idea how to crate a disc would be to try to scan a spiral. A circle can be created by two sine waves that have a phase shift of 90 °. If I now could apply a frequency and amplitude sweep, so that the circle gets smaller and smaller and with that the frequency of the wave increases such that the speed of the beam stays constant, I think it should be possible!

But, first, I have no idea who to calculate the parameters of the amplitude and frequency sweep and, second, since this sweep is not linearly, can I define any user-defined sweep?

Maybe there are other ideas how to scan a disc?

I would be very happy if somebody could come up with any ideas, either about how to do that spiral scan or about how to scan a disc with other voltage patterns.

Best regards
Sternhagel

Edited by: Sternhagel on Aug 6, 2013 9:33 AM