Beam profile pictures (26/08/04)

These are taken with the tube at a temperature of 4 degrees and a reasonably high pressure (~10 Torr). The LCD sheet was about 1m from the OC for each.







I think I'm correct in saying that this is "higher mode" (i.e. TEM11, TEM12 etc) operation. Which is not good since most power is obtained from the TEM00 mode (i.e. a single spot).

I tried lowering the pressure (still at 4 degrees):

I then raised the temperature to 20 degrees to see if the pattern persisted:





Yup, it's still there. Possibly not as many modes as at the lower temperature?

I then made the (possible) mistake of tweaking the OC. Tried the LCD panel again and guess what I got?

Back to a single spot! I tried setting the OC just off alignment to get the pattern back again but to no avail. I tried the tube down at 4 degrees again but still no luck.

All extremely nice....does anyone know how I can force it to lase in one of the higher order modes? Would placing say a wire across the cavity help, so it prevented oscillation in a particular direction?

Here are some scans of fax paper I burned with the laser

1) Click here. These are the trails I mentioned. Notice the "triplets" (or even quadruplets) of dots in some of the trails.

2) Click here. The burn pattern produced at 4 degrees.

3) Click here. The burn pattern produced at 20 degrees.