Spectrometer setup
In the setup, the team used sum frequency generation in a PPLN nonlinear waveguide to up-convert photons from the NIR to the visible range. Specifically, Zhang and colleagues add together the frequencies of a 1550 nm pump beam and a 1310 nm signal beam to achieve visible light at 702 nm. This up-converted light is then detected by a single photon counting module.
Image Credit: Qiang Zhang