Speaker
Description
Measurements are the cornerstone of physics. Precision measurements and sensing at mid-infrared (MIR) wavelengths remain complicated by the limited availability of low-noise detectors between 1000 and 10000 nm. Warm alkali metal vapors have long served as a versatile, low-cost platform for spectroscopy and nonlinear optics.
Here we explore hot atomic rubidium vapor to drive the Doppler-free two-photon transition $5S_{1/2} - 5P_{3/2} - 5D_{5/2}$ with 778nm light, which emits the cascaded 5.2 $\mu$m and 420nm (blue fluorescence).
Induced coherence is a technique, which allows to interfere two independently generated light beams, which originate from a non-linear optical process. Historically, two independently pumped photon pair sources were used to produce signal and idler beams. When the generated idler photons are aligned and rendered indistinguishable, coherence is induced between the otherwise independent signal photons. Naturally, the wavelength of signal and idler can be vastly different, such the detection of one testifies the interference of the other. This scheme has been extended to application including imaging with undetected photons, nonlinear interferometry and infrared spectroscopy. This positions the undetected idler beam as a means of encoding information that is only retrieved through the detected visible signal.
Meanwhile, atomic vapors have proven to allow for highly non-linear optical transitions and paired photon generation. In hot rubidium vapor, a strong pump field around 778nm results in (5.2$\mu$m) MIR and visible (420nm) fluorescence, which emerges from the consecutive decay steps of the cascade. In our experiment, we overlap the mid-infrared emission with the pump field and record interference of the 420nm component. This testifies the interaction on the near-infrared wavelength.