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ENS Cachan - Laboratoire de photonique quantique et moléculaire

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Optimization of point spread function of a high numerical aperture objective lens:Application to high resolution optical imaging and fabrication

le 15 décembre 2014
A 14h00 - Auditorium Daniel Chemla (Institut d'Alembert)

Qinggele LI

Nowadays, far field optical microscopy is widely used in many fields, for fundamental research and applications. The low cost, simple operation, high flexibility are its main advantages. The key parameter of an optical microscope is the objective lens.
This thesis's work focuses mainly on the characterization and optimization of the point spread function (PSF) of a high numerical aperture (NA) objective lens (OL) for applications of high resolution imaging and nano-fabrication.
In the first part of the thesis, we have systematically investigated the dependency of polarization and intensity distributions of the focusing spot on numerous parameters, such as the phase, the polarization, and the beam mode of incident beam, as well as the refractive index mismatch. Then, we demonstrated theoretically different methods for manipulation of the polarization and intensity distributions of the focusing spot, which can have desired shapes and are useful for different applications. By using a home-made confocal microscope, we have experimentally verified some of the theoretical predictions, for example, vector properties of light beam under a tight focusing condition. In the second part of dissertation work, a new, simple and inexpensive method based on the one-photon absorption mechanism has been demonstrated theoretically and experimentally for  3D sub-micrometer imaging and fabrication applications. The theoretical calculation based on vectorial Debye approximation and taken into account the absorption effect of material shows that it is possible to focus the light tightly and deeply inside the material if the material presents a very low one-photon absorption (LOPA) at the excitation wavelength. We have then demonstrated experimentally that the LOPA microscopy allows to achieve 3D imaging and  3D fabrication with submicrometer resolution, similar to those obtained by two-photon absorption microscopy.
Type :
Séminaires - conférences, Thèses - HDR

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