A major milestone towards the ion clock was reached today: we trapped the first Strontium ions!
This involves first heating a dispenser that contains Strontium atoms with about 4-5 W (4 A and 1 V). The atoms that fly out of the dispenser are then photoionized using two blue lasers, one at 461 nm and another at 405 nm (we use a laser from a blue-ray drive for this!). We now have Sr+ ions that can be trapped in a Paul trap. A high-voltage (300 Vpp) ~10 MHz sine-wave is applied to the electrodes of the trap. Another blue laser at 422 nm is then used both for laser-cooling and as a means to detect the ion. What we see in the video is the ion fluorescence at 422 nm when it jumps down to the ground state from an excited state. The excited state can also decay into a dark state and we need a re-pump laser at 1092 nm to keep the ion in the Doppler cooling cycle. The fluorescence emitted from one or a few ions is very weak, and we used an image-intensifier and a CCD camera with 500 ms to 1 s exposure time for this video.
The camera software produces FITS frames as output. I used these commands to make the video:
1234 mogrify -format png *.fts # convert to PNGmogrify -crop "640x480+436+315" +repage *.png # crop to the interesting areamogrify -contrast-stretch 10x100 *.png # improve contrastffmpeg -r 3 -f image2 -i 'myframes_%02d.png' -qscale 1 'video.avi'
On the last line "3" is the desired frame-rate of the output. I then concatenated a few of these videos together with
12 mencoder video1.avi video2.avi -mf fps=3 -oac copy -of lavf -ovc copy-lavcopts aglobal=1:vglobal=1:coder=0:vcodec=mpeg4:vbitrate=4500 -vf scale=1280:720 -o output2.mp4