Demonstrate a proper TD‑fNIRS instrument response (DTOF histogram) with the prototype

Demonstrate a proper time-domain fNIRS instrument response function by producing sufficiently short optical pulses in the gain-switched laser diode and acquiring a distribution-of-time-of-flights histogram using the APD/SiPM detector and the Red Pitaya TDC in the proposed prototype.

Background

The authors assembled a full time-of-flight measurement chain (laser driver, single-photon detector, and a TDC on an FPGA platform). However, short enough optical pulses could not be generated with the current laser diode driver configuration, preventing acquisition of a proper DTOF histogram.

Establishing the instrument response is a prerequisite for validating overall timing performance and for proceeding to tomographic reconstructions with the prototype.