Abstract

Cavities have become a very important tool for scientific research and for industrial applications like lasers and detectors because of the outstanding ability of field enhancement that increases the light-matter interaction. Therefore a goal ever since was to increase the field enhancement by improving the mirrors of optical cavities. This research leaded to very good mirrors with a mirror loss of 1.6 × 10⁻⁶ and a cavity finesse of 1.9 × 10⁶ [1]. In a time of steady micro-miniaturization we follow a different receipt for increasing the cavity field enhancement, namely, the reduction of the size of the cavity, as the light-matter coupling strength is inversely proportional to the square root of the mode volume [2]. Extremely high field confinement is obtained with plasmonic resonators that reach cavity mode volumes smaller than 10⁻³ of λ³ for metal-insulator-metal (MIM) designs [3]. Despite the moderate quality (Q) factors the high field enhancement enables to explore the limits of light-matter interaction [4]. The same feature of a cavity enhances the nonlinear effects in matter, resulting e.g. in an effective nonlinear frequency conversion. Those processes can be further improved using tailored high nonlinear susceptibility materials such as semiconductor quantum wells (QW) [5]. Recently, Lee et al. demonstrated experimentally a second harmonic conversion efficiency of 2 × 10⁻⁶ W/W² in the mid infrared [6] using doubly resonant plasmonic resonator arrays coupled to intersubband transitions [ISBT] in QWs. Furthermore, theoretical investigations predict a conversion efficiency of 1.3 × 10⁻² W/W² with split ring resonators strongly coupled to ISBTs [7].

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