Pmt1001

PDMS phantoms as prepared above were charged for 10 s by a 365-nm LED at 0.13 mW/mm², and a photomultiplier tube (PMT1001; Thorlabs, Newton, NJ) was put in the close vicinity of the phantom to collect the persistent luminescence after the charging light was turned off. The output voltage from the PMT, which exhibits a linear dependence on light intensity, was then collected with a multifunction input/output (I/O) device (NI USB-6221, National Instruments, Austin, TX).

Regarding the detection part, this system is designed to detect NAD(P)H from the 3PAF channel and FAD from the 2PAF channel, combined with noncentrosymmetric structures from the SHG channel and interfacial features from the THG channel, all simultaneously. The reflected multimodal multiphoton signals were spectrally-separated into four detection channels by long-pass dichroic mirrors and appropriate band-pass filters, as shown in Fig. 1. To minimize the crosstalk between individual channels and maximize the detection efficiency of each channel, the four channel filters were chosen with specific bandwidth characteristics and listed in Fig. 1. For this system, the high pulse peak power can enable more than one photon excitation per pulse when operating at low repetition rates. Therefore, the spectrally-separated signals were detected by analog PMTs instead of photon-counting PMTs (PMT2101, Thorlabs for 3PAF/ 2PAF/ THG channels; PMT1001, Thorlabs for SHG channel).