The project seems to call for the smallest detectors. I'm buying a few each of 'all'* the little PD's from digikey. (I can share a list if someone wants... it's a mix of TH and SMD.) C_in between 1-3 pf when reversed biased. I don't see how it makes sense to bootstrap or cascode the PD**. So I was looking at opamps with small C-in. (Big thanks to H&H of AoE as always.) I've now got a column of 1/f corner freq. of e_in (input voltage noise) for the small C_in fet opamps. In table 4x.2 of the x-chapters. The best looks to be the ADA4817. 1/f ~10 kHz. (hard to tell.. bit of a swoopy noise graph.) (C_in = 1.5 pF, e_in = 4 nV/rthz.)
Pure 1/f noise into a TIA must give a constant noise voltage.. till hit by the GBW of the opamp. (is that right? I'm being mathematically lazy and just tipping the slope of the graph.)
George H.
*not all, but a selection. **I'm not sure how to guesstimate the C of a cascode, and are there any small bjt's left? (The bft25a is listed as 'not for new designs' on DK) *** 100kHz is common and higher.