1 MOhm, 4 MHz photodetector

One-Inch-Photodetector (https://github.com/aewallin/One-Inch-Photodetector) with 1 MOhm transimpedance, a larger Hamamatsu 5791 photodiode, and OPA657 op-amp.

Achieves around 4 MHz bandwidth, which should be OK for intensity monitoring etc. This will work only for quite small powers, since the maximum DC output swing is 5V, corresponding to a 5 uA photocurrent, or around 12 uW if we assume 0.4 A/W responsivity for the photodiode.

Again I needed to tweak the TIASim simulation to make the experimental data fit the model. I now suspect this is due to capacitive loading of the op-amp output. This should be possible to test by connecting the detector directly to the Spectrum Analyzer input, and then adding successively longer cables and seeing if the response changes.

April Fools Ion

Despite the lockdown, some trapping in the lab this week. First single-ion experiments this year, after the 405 nm laser broke in January. Not much going on in these videos, but at least it's a single ion!

Sigma=60 Hz for the AOM frequency, so FWHM ~120 Hz AOM, and FWHM 240 Hz optical.

First clock-transition linewidth measurement give about a 200 Hz wide transition, so around 5e-13 fractionally.