The home stretch

A lot has happened since my last post. Julien and I went to the C2RMF again last Thursday. After some unsuccessful attempts to get the microtopography apparatus to function, we performed optical microscopy and SEM on KETH kurai, the Roman coin, and AN43U. Bad news first: we did absolutely nothing to the Japanese coin. I suppose the fluence we were using (~150 mJ/cm^2) wasn't quite enough to break through the corrosion layer. The ablation marks on the Roman coin were visible with naked eye.
The correct description for this coin is:
a.) Toasted
b.) Well done
c.) It resembles R2D2 after the battle of the first Death Star
d.) All of the above

If you picked d., congratulations! Yeah, so we hit this coin with way too much energy. From right to left (i.e. most to least visible) the craters are from 1000, 500, 100, 50, 10, 5, and (barely visible) 1-2 pulses. I say 1-2 because the shutter isn't good enough to reliably pick off one shot. The second smaller spot is probably due to a ghost reflection off of the dielectric mirror, but evidently it carried enough energy to ablate the coin. Unfortunately, the day I shot at the Roman coin the energy meter was missing, and the following day Rod and Xiaowei tinkered with the laser, so I don't know the total energy in the pulse train. Using the equation that avg energy = average power/ rep rate, and using the spot size measured with the CCD camera, I estimate that the large spot is approximately 11.5 J/cm^2 while the small spot is 2.5 J/cm^2. That would explain the char marks.

I was pleasantly surprised with the nickel. Nothing was visible, even under the optical microscope at 20x visibility, but the SEM showed otherwise.
The lines are, from right to left: 500, 100, 50 (higher rate), 10, and 5 pulses incident. The ablation spots are really quite nice, and the EDX results show a successful removal of corrosion products.

On Friday, we had a group meeting with Dr. Mourou. I showed him the SEM results and he seemed happy with them. I really wish I had more time to do research now that the setup is functioning and none of the pieces are missing.

I spent Friday and today making my presentation for Wednesday. The students are meeting with Steve Yalisove tomorrow to discuss the projects/summer overall, and everybody is giving presentations on their work Wednesday.