Abstract
Direct detection of single photons at wavelengths beyond 2 microns under ambient conditions remains an outstanding technological challenge. One promising approach is frequency upconversion into the visible (VIS) or near-infrared (NIR) domain, where single photon detectors are readily available. Here, we propose a nanoscale solution based on a molecular optomechanical platform to up-convert photons from the far and mid-infrared (covering part of the THz gap) into the VIS-NIR domain. We perform a detailed analysis of its outgoing noise spectral density and conversion efficiency with a full quantum model. Our platform consists in doubly resonant nanoantennas focusing both the incoming long-wavelength radiation and the short-wavelength pump laser field into the same active region. There, infrared active vibrational modes are resonantly excited and couple through their Raman polarizability to the pump field. This optomechanical interaction is enhanced by the antenna and leads to the coherent transfer of the incoming low-frequency signal onto the anti-Stokes sideband of the pump laser. Our calculations demonstrate that our scheme is realizable with current technology and that optimized platforms can reach single photon sensitivity in a spectral region where this capability remains unavailable to date.
Highlights
Many applications in security, material science, and health care would benefit from the development of new technologies for far- and mid-infrared (FIR and MIR, respectively) detection and thermal imaging [1]
We presented a new concept for frequency upconversion from the mid-infrared to the visible domain based on the interaction of both fields with molecular vibrations coupled to a dual-resonant nanoantenna
We considered an incoming long-wavelength infrared radiation that resonantly excites a vibrational mode, which is simultaneously coupled through its Raman polarizability to a coherent pump field at a shorter wavelength, resulting in upconversion of the IR signal onto the anti-Stokes sideband of the pump
Summary
Material science, and health care would benefit from the development of new technologies for far- and mid-infrared (FIR and MIR, respectively) detection and thermal imaging [1]. Our strategy consists in converting the incoming low-frequency signal onto the anti-Stokes sideband of a pump laser in the VIS-NIR domain, where detectors with single-photon sensitivity are readily available [7,8] This approach is inspired by the recent realization of coherent frequency conversion using different types of optomechanical cavities [9,10,11,12,13,14,15] and is conceptually distinct from a recently demonstrated detection scheme assisted by a microfabricated resonator [16]. We illustrate the achievable performance with a device operating at 30 THz (10 μm) and find internal conversion efficiencies on the below order 10−12 of apfffieffiwffiffiffiffi W= Hz. percent and noise-equivalent power we demonstrate how our approach may be used to reach single-photon detection at frequencies down to approximately 5 THz. pffiffiffiffiffiffiffi NIRgIR;0 is the collective resonant vacuum coupling rate of the vibrational mode ν for NIR identical molecules, and n IR the mean occupation of the IR antenna mode. ΚIR 1⁄4 κIeRx þ κI0R is the loss rate of the antenna at the incoming frequency, which is the sum of the external decay rate κIeRx (by radiative coupling to far-field modes) and the internal decay rate κI0R (by absorption in the metal). ηIR 1⁄4 κIeRx=κIR is the coupling ratio of the antenna and Γtot the total vibrational decay rate, where the intrinsic vibrational linewidth Γν is modified by its coupling to the IR antenna [25] and the optomechanical interaction with the pump laser, as explained below
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