Investigating the evanescent field

  • Responsible : Tristan SFEZ, Libo YU, Matthieu ROUSSEY
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Near-field techniques overcome the fundamental diffraction limit in optical microscopy. One way of detecting the near field is carried out by using a nanoscale aperture collecting the electromagnetic field in close proximity to the sample surface. To characterize exactly an electromagnetic field, intensity alone is not sufficient; one has to know its amplitude, phase and polarization.

Figure 1 . Photography of a probe mounted on a tuningfork

The OPT Lab has developed a Scanning Near-field Optical Microscope (SNOM) implementing a multi-heterodyne scheme with the aim of measuring the amplitude, the phase and the polarization properties of structures within the near field. The goal is to improve the basic understanding of near-field phenomena and to provide a direct visualization of the optical field behavior within nano-fabricated devices.

Figure 2 . Observation in the near field of a Bloch Surface Wave

Actual Projects in this field:

  • SNF project NIPP ‘Nano-Imaging with Phase and Polarization: Using multi-heterodyne scanning near-field optical microscopy (SNOM) for nanostructure characterization’, n° 200020-105354
  • SNF project ELF ‘Engineered Local Field’ n°200021-117930


  • [1] Benfeng Bai, Xiangfeng Meng, Janne Laukkanen, Tristan Sfez, Libo Yu, Wataru Nakagawa,Hans Peter Herzig, Lifeng Li, and Jari Turunen, Phys. Rev. B, 80, 035407 (2009)
  • [2] Emiliano Descrovi, Tristan Sfez, Lorenzo Dominici, Wataru Nakagawa, Francesco Michelotti, Fabrizio Giorgis and Hans-Peter Herzig, Opt. Express, 16 (8) 5453-5464 (2008)
  • [3] Tristan Sfez,Emiliano Descrovi, Lorenzo Dominici, Wataru Nakagawa, Francesco Michelotti, Fabrizio Giorgis, and Hans-Peter Herzig, App. Phys. Lett., 93, 061108 (2008)

Nano-Structure devices: simulations – fabrication & characterization

  • Responsible : Matthieu ROUSSEY
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The OPT Lab is investigating the interaction of light with structures where the important length scale is from a few hundred nanometers down to just a few nanometers. The study of nano-optics requires knowledge from various areas: theoretical studies are needed to predict and understand the behavior of light in such environments, highly sensitive and precise equipment has to be designed and built to test the theoretical predictions, and cutting-edge technologies are required for the fabrication of the tiny structures used for this research. The present research fields include photonic crystals, engineered local fields, nano-particles and optical memory.

Simulation of the behavior of light in subwavelength structures

(Vincent PAEDER, Qing TAN)

Simulations are at the beginning of each study in the domain of nano-structures. The prediction of behavior of light in such devices is not obvious and requires other techniques than analytical method. In the OPT Lab, different methods are used, from homemade codes or commercial software such as FDTD (finite difference time domain), RCWA (rigorous coupled wave analysis) or PWE (plane wave expansion) for example. The principal goal of our studies is to design sensors with the highest sensitivity and the smallest size.

Figure 1. 3D FDTD Simulations of a sensor based on nano-slots in gold layer.

Structure materials at the nano-scale

(Armando COSENTINO, Yu Chi Chang)

The fabrication of nano-structures is performed in clean room thanks to different high and precise techniques and equipment such as electron beam lithography, lift-off,
reactive ion etching in the clean room of the OPT Lab and partially in the CMI (Center of MicroNano Technology / EPFL) also.

Figure 2. SEM picture of photonic crystal cavity on silicon membrane fabricated by e-beam lithograpy.

Measure of transmission and reflection

Measuring variation of intensity in transmission or reflection or distinguish displacement of a spotlight of few micrometers is generally the methods used to characterize the nano-photonic samples. The main application for our devices is the sensing and this project is linked with bio-photonics projects.

Figure 3. Measurements of a superprism effect.

Simulation of nano-structure for solar cell optimization

(Ali Naqavi in collaboration with PVLAB)

As the demand for energy grows during time, solar cell technology attracts more attention as a major candidate to provide green power generation. Advancing a viable market for photovoltaic solar energy requests for making a balance between the efficiency of solar cells and their cost. Thin-film photovoltaic cells which use much less raw material compared to wafer-based solar cells can lead to a significant price cut; however, they need light trapping techniques to exhibit acceptable performance. Our aim, here, is semi-analytical or numerical simulation of light-matter interaction in thin film solar cells to optimize their structure using periodic or random interfaces.

Figure 4. Simulation of field enhancement in a grating for a solar cell.

Actual Projects in this field:

  • SNF project ELF ‘Engineered Local Field’ n°200021-117930
  • SNF project ‘Interface texturing for light trapping in solar cells’
  • SNF project NIPP ‘Nano-Imaging with Phase and Polarization: Using multi-heterodyne scanning near-field optical microscopy (SNOM) for nanostructure characterization’, n° 200020-105354


[1] P.-Y. Baroni, B. Päivänranta, T. Scharf, W. Nakagawa, M. Roussey, M. Kuittinen, H. P. Herzig, J. Eur. Opt. Soc. R. P. 5, 10006 (2010)