Optical gating in photodetector for femtosecond time-resolved imaging

Non-degenerate two-photon femtosecond gating directly within a photosensor has been investigated in both external and internal photoeffect configurations, with the aim of enabling fast time-resolved imaging applications. This method of gating eliminates the need for the bulky and alignment-sensitive conventional setup that requires separate elements for gating and sensing. For a K2CsSb photocathode, the energy conditions of the participating photons have been established, and the method's time resolution and sensitivity have been quantitatively evaluated. For the first time, the use of non-degenerate two-photon absorption in a multi-pixel CMOS sensor for ballistic imaging through a scattering medium-without mechanical scanning-has been experimentally demonstrated, revealing a significant improvement in image contrast over conventional singlephoton imaging.