Integration of a superconducting nanowire detector into a confocal microscope for TRPL-mapping: Sensitivity and time resolution

Superconducting Nanowire Single Photon Detectors (SNSPDs) were introduced to the market in 2003 and are used in multiple quantum optics applications, due to their outstanding properties such as fast instrument response and high quantum efficiency. The high quantum efficiency is important for materials science applications with emission in IR-range >1000 nm, where other available single photon detectors have a low sensitivity, high dark noise, and slow time response. We have integrated a SNSPD (Single Quantum) into a confocal photoluminescence lifetime microscope MicroTime 100 (PicoQuant) in order to compare the performance of different SNSPD designs with a standard IR-PMT for time-resolved photoluminescence (TRPL) measurements and imaging of IR sample e.g., CIGS device. One used SNSPD channel was a classical single mode fiber coupling to guide the light onto the sensor, the other channel used an internal multimode fiber instead. We achieved a significant increase in photoluminescence sensitivity in both designs compared to a standard IR-PMT, as well as a several times higher sensitivity of the multimode-fiber coupled nanowire compared to the singe-mode fiber one, despite comparable photon quantum efficiencies in this wavelength range. The increased sensitivity combined with the lower dark count rate resulted in an increase of signal-to-noise ratio by more than 2 orders of magnitude compared to the IR-PMT. The high sensitivity of SNSPDs combined with high temporal resolution (instrument response function of this setup was below 100 ps) allows to identify and investigate highly quenched signals of samples even at low illumination levels. The integration of the SNSPD detector to a scanning confocal microscope will also enhance the capabilities in field of single oxygen sensing and cell imaging in NIR by using NIR emitting dyes or nanoparticles without autofluorescence.