Koheron PDX10B-SI is a Si free-space balanced photodetector with 80 kV/A transimpedance gain and 8 MHz bandwidth. With a noise-equivalent power spectral density of only 1 pW/√Hz and the capability to reject laser common mode noise, the photodetector can be shot-noise limited even at a low input signal level. A monitoring input signal is provided for each photodiode to assist with beam alignment and power balancing.