Quantum Stimulated Emission Spectroscopy

Stimulated emission has a wide variety of useful applications including biomedical sensing. One of the drawbacks of stimulated emission is high background noise from the excitation laser and the sample's fluorescence. We propose and demonstrate the use of entangled photons to enhance the detection of stimulated emission photons and better distinguish the signal from noise. A BBO crystal is pumped with a blue laser to produce Spontaneous Parametric Down-Converted entangled photon pairs. The photons are then split down two paths, one path going to a detector the other going through the sample as a stimulating photon. The stimulating path is split again so that the stimulated and stimulating photons go to separate detectors. A stimulated emission signal is detected when 3-way coincidence is measured. The wavelengths measured are chosen using bandpass filters tilted to the appropriate angle, enabling spectroscopic measurements of the stimulated emission. This setup allows for tuning of the wavelength of measured stimulated emission without having to change the stimulated source itself, and is sensitive to weak signals which would benefit imaging, and Raman spectroscopy applications.