Broadband low-noise photodetector for Pound-Drever-Hall laser stabilization

The Pound-Drever-Hall laser stabilization technique requires a fast, low-noise photodetector. We present a simple photodetector design that uses a transformer as an intermediary between a photodiode and cascaded low-noise radio-frequency amplifiers. Our implementation using a silicon photodiode yields a detector with 50 MHz bandwidth, gain $> 10^5$ V/A, and input current noise $< 4$ pA/$\sqrt{\mathrm{Hz}}$, allowing us to obtain shot-noise-limited performance with low optical power.