Revisiting cavity-coupled 2DIR: A classical approach implicates reservoir modes.

Significant debate surrounds the origin of nonlinear optical responses from cavity-coupled molecular vibrations. Several groups, including our own, have previously assigned portions of the nonlinear response to polariton excited-state transitions. Here, we report a new method to approximate two-dimensional infrared spectra under vibrational strong coupling, which properly accounts for inhomogeneous broadening.

Multi-Gb/s free-space laser communication at 4.6-μm wavelength using a high-speed, room-temperature, resonant-cavity infrared detector (RCID) and a quantum-cascade laser.

Research has shown that free-space laser communication systems may experience fewer outages due to atmospheric impairments such as haze, fog, clouds, and turbulence by operating at a longer wavelength in the mid-wave or long-wave infrared, if disadvantages such as lower-performance transceiver components may be overcome. Here we report a resonant cavity infrared detector (RCID) with 4.6-µm resonance wavelength that enables 20-dB larger link budget than has been reported previously for ∼ 5 Gb/s operation.

Detection of dimethyl methylphosphonate (DMMP) with an interband cascade laser sensor.

We demonstrate the sensitive detection of dimethyl methylphosphonate (DMMP, a hydrogen-bond (HB) basic phosphonate ester) using additional optical loss induced in an interband cascade laser with top optical cladding layer replaced by an exposed sensing window coated by a HB acidic sorbent layer. Thin coatings of the sorbents HCSFA2 and oapBPAF were deposited on the sensing window to allow reversible capture and concentration of DMMP for optical interrogation. Analyte levels down to 0.

Midwave resonant cavity infrared detectors (RCIDs) with suppressed background noise.

We report a resonant cavity infrared detector (RCID) with an InAsSb/InAs superlattice absorber with a thickness of only ≈ 100 nm, a 33-period GaAs/AlGaAs distributed Bragg reflector bottom mirror, and a Ge/SiO/Ge top mirror. At a low bias voltage of 150 mV, the external quantum efficiency (EQE) reaches 58% at the resonance wavelength λres ≈ 4.6 µm, with linewidth δλ = 19-27 nm.

Control, Modulation, and Analytical Descriptions of Vibrational Strong Coupling.

Here, we review the design of optical cavities, transient and modulated responses, and theoretical models relevant to vibrational strong coupling (VSC). While planar Fabry-Perot cavities remain the most common choice for experiments involving vibrational polaritons, other choices including plasmonic and phononic nanostructures, extended lattice resonances, and wavelength-scale three-dimensionally confined dielectric cavities have unique advantages, which are discussed. Next, we review the nonlinear response to laser excitation of VSC systems revealed by transient pump-probe and 2DIR techniques.