Here's another one-inch-photodetector using OPA818 with a 2pF@5V InGaAs fiber-coupled photodiode FGA01FC. With a transimpedance gain of 4k7 Ohms the bandwidth is just over 200 MHz. A TIASim model predicts the dark-noise and response reasonably well with a parasitic capacitance (over RF) adjusted to ca 0.12 pF. The spectrum-analyzer settings weren't ideal for looking at the dark-noise which should go down to the thermal-noise of the 4k7 resistor (dashed line) - but here the instrument noise-floor prevents us from seeing that.
88Sr+ clock with new mu-metal magnetic shields
With new thicker solid mu-metal magnetic shields (2 layers), the clock transition in our 88Sr+ experiments shows a transform-limited linewidth of ca 10 Hz using a 72ms probe pulse. More testing to follow, as we try to lengthen the probe-pulse and search for the ultimate linewidth limit.
Fiber optic power meter test
Farnell is now selling a dirt-cheap (28 euros or so) Multicomp fiber optic power meter, so here's a quick comparison against other power meters in the lab.
It looks like the 28 euro meter performs good enough for most tasks in the lab. The Multicomp only has a few fixed wavelength settings, while the Thorlabs is adjustable in 1nm steps.
