Abstract:We present the first optical sensor based on Surface Plasmon Resonance (SPR) operating in the mid-infrared range. The experimental setup is based on a Kretschmann geometry with Ti/Au layers deposited on a CaF 2 prism where light excitation is provided by a Quantum Cascade Laser (QCL) source. Evidence of SPR is presented and the sensing capability of the system is demonstrated by using CO 2 and N 2 mixtures as test samples. Due to the absorption of CO 2 at this wavelength, it is shown that the sensitivity of this configuration is five times higher than a similar SPR sensor operating in the visible range of the spectrum.

We demonstrate high spectral control from surface emitting THz Quantum Cascade Lasers based on a two-dimensional photonic crystal cavity. The perforated top metallic contact acts as an in plane resonator in a tight double-metal plasmonic waveguide providing a strong optical feedback without needing three-dimensional cavity features. The optical far-field patterns do not exhibit the expected symmetry and the shape of the cavity mode. The difference is attributed to a metal surface plasmon mediated light outcoupling mechanism also responsible for the relatively low extraction efficiency.

The authors fabricate and characterize a series of quantum cascade laser micropillars emitting at ≈3.5THz. The optical confinement by double plasmon guiding in the vertical direction creates a large impedance mismatch between the confined optical modes and free space. Thus, unlike standard dielectric structures, large quality (Q) factors are maintained for small radius to wavelength ratios. The narrow bandwidth of the optical mode results in low threshold current (8mA) single-mode lasers. Cavity pulling enables a fine dynamic tuning of the emission wavelength. Comparison of the frequency shift due to cavity pulling and the Stark effect provides an experimental measure of the gain (36cm−1).

Direct experimental evidences for excitonic lasing is obtained in optically pumped V-groove quantum wire structures. We demonstrate that laser emission at a temperature of 10 K arises from a population inversion of localized excitons within the inhomogenously-broadened luminescence line. At the lasing threshold, we estimate a maximum exciton density of about 1.8 105cm-1.Comment: 11 pages, 4 figures, submitted to Phys. Rev.

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