Giant optical field enhancement in multi-dielectric stacks by photon scanning tunneling microscopy

Abstract

International audienceDielectric optical thin films, as opposed to metallic, have been very sparsely explored as good candidates for absorption-based optical field enhancement. In such materials, the low imaginary part of the refractive index implies that absorption processes are usually not predominant. This leads to dielectric-based optical resonances mainly via waveguiding modes. We show here that when properly designed, a multi-layered dielectric thin films stack can give rise to optical resonances linked to total absorption. We report here, on such dielectric stack designed to possess a theoretical optical field enhancement above 1000. Using photon scanning tunneling microscopy, we experimentally evaluate the resulting field enhancement of the stack as well as the associated penetration depth. We thus demonstrate the capability of multi-dielectric stacks in generating giant optical field with tunable penetration depth (down to few dozens of nm)

Bandwidths limitations of giant optical field enhancements in dielectric multi-layers

“…1 gives the used parameters to described an optimized DM with an imaginary index n p in the top layer, and with the resonance angle θ R and wavelength λ R . We recently reported on the experimental and numerical variations of the reflectance of such DM while varying the incident angle (θ) around θ R and extracted the field enhancement for various incident angles using near field scanning optical microscopy [16,25,26]. Let's now focus on the effects of the illumination conditions over the resonance, starting with the spatial divergence and followed by the spectral bandwidth.…”

“…Finally, optical near field measurements have also been done by Descrovi et al [24] evidencing an enhancement factor of 100 over a dielectric multi-layer. And more recently we measured an enhancement factor of 300 for an optimized dielectric multi-layer [25,26]. By supporting large field enhancements, dielectric multi-layers are also envisioned for sensing applications, where they are typically compared with surface plasmon resonances as related in [27][28][29], or combined with plasmon effect as Tamm plasmon [30] or in Fano resonance with giant field enhancement [31].…”

Linearly decayed evanescent optical field in planar refractive index well

“…Evanescent field excitation has been playing important roles in fluorescence and Raman scattering studies on molecular analytes at surface/interfaces [12,13]. Enhancement of evanescent field based on one dimensional photonic crystal (1DPC) supported Block surface wave (BSW) makes the evanescent field excitation a promising tool in micro and nano scale analysis on materials in molecular level, and in sensing applications [14][15][16][17][18]. However, due to the usually rapid exponentially decaying property, the optical field is inhomogeneous even in the range of penetration depth of the evanescent field [14], so that the signals to be detected are inhomogeneous, especially for molecules with 3d structures [12].…”

“…Enhancement of evanescent field based on one dimensional photonic crystal (1DPC) supported Block surface wave (BSW) makes the evanescent field excitation a promising tool in micro and nano scale analysis on materials in molecular level, and in sensing applications [14][15][16][17][18]. However, due to the usually rapid exponentially decaying property, the optical field is inhomogeneous even in the range of penetration depth of the evanescent field [14], so that the signals to be detected are inhomogeneous, especially for molecules with 3d structures [12]. The LDEF analyzed above provides an option to build a homogeneous evanescent field that could be flexible for different analytes of micro to nanometer sizes, and could be a tool of sensing to those specimens contained in solutions or gases.…”

Sensitivity of resonance properties of all-dielectric multilayers driven by statistical fluctuations

“…Numerous work have been reported on dielectric multilayers optimization using both Bloch surface waves [1][2][3][4][5][6][7][8][9][10][11][12][13] or admittance formalism in the total internal reflection conditions [14][15][16][17][18][19] towards giant field enhancement generation [20][21][22][23][24][25][26][27]. Because of the geometric similarities, the optical response of the optimized dielectric multilayers (DM) is often compared [28][29][30][31] with plasmon excitation [32][33][34][35][36] in metal thin films [37].…”