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Tomographie optique de diffraction
There is considerable interest in developing optical microscopes presenting a lateral resolution below the usual Rayleigh criterion, λ/(2NA), where λ is the wavelength of the illumination and NA is the numerical aperture of the imaging system, while retaining the convenience of far-field illumination and collection.
Among the various ways to ameliorate the resolution, it has been proposed to illuminate the sample with many structured illuminations, namely standing waves, and to mix the different images through simple arithmetics.This technique is very close to optical diffraction tomography (ODT) in which the sample is illuminated under various angles of incidence, the phase and intensity of the diffracted far-field is detected along several directions of observation, and a numerical procedure is used to retrieve the map of the permittivity distribution of the object from the far-field data. Experimental and theoretical studies have shown that using several illuminations permits one to exceed the classical diffraction limit by a factor of two.
In all microscopy techniques using several successive illuminations, one needs a numerical procedure to combine the different images and extract the map of the relative permittivity distribution of the object from the scattered far-field. In general, one assumes that the object is a weak scatterer so that there is a linear relationship between the scattered field and the relative permittivity of the object, namely one assumes that the Born approximation is valid. In this case, the transverse resolution limit can be inferred from simple considerations on the portion of the Ewald sphere that is covered by the experiment. It is limited by λ/2(ni+nd) for configurations in which the incident waves propagate in a medium of refractive index ni, while the diffracted waves propagate in a medium of refraction index nd.
In this web page we present a brief overview of our research in optical diffraction tomography. For more details on each topic have a look at the references.
Tomographic diffractive microscopy achieves a resolution about λ/4
Tomographic diffractive microscopy with a wavefront sensor
Nanometric resolution using far-field optical tomographic microscopy
Mirror-assisted optical diffraction tomography
Experimental Demonstration of Quantitative Imaging beyond Abbe’s Limit
Beyond the Rayleigh criterion : Grating assisted far-field optical diffraction tomography
Influence of multiple scattering with optical diffraction tomography
Superresolution in total-internal reflection tomography
Tomographic diffractive microscopy achieves a resolution about λ/4
We have developed the first optical digital microscope that exploits all the information accessible via the diffraction process : intensity, phase, and polarization state of the scattered field for any possible illumination within the numerical aperture of the objective. In the single scattering regime, this ultimate microscope is able to reconstruct permittivity maps with a resolution about one-fourth of the wavelength. This experimental achievement, which outperforms that of all existing far-field microscopes, points out the importance of accounting for light polarization when tackling super resolution and sets a landmark in optical far-field imaging.
To document further the potential of the full-polarized TDM, we image a complex sample made of twelve resin rods of width 100 nm, length 300 nm, and height 140 nm radially placed at the summit of a dodecagon [Fig. 7(a)].
The sample is illuminated by eight directions of incidence, defined by a fixed polar angle 60- degres and an azimuthal angle regularly spaced within 360 degres. (a) Scanning electron microscope image. (b) Dark-field optical microscope image. (c) Reconstructed permittivity averaged over the sample’s height using full-polarized TDM data. (d) Permittivity along the dashed circle in (c). Plain line : full-polarized data ; dashed line : the combined scalar data.
Reference :
- T. Zhang, Y. Ruan,1 G. Maire, D. Sentenac, A. Talneau, K. Belkebir, P. C. Chaumet and A. Sentenac, Full-polarized Tomographic Diffraction Microscopy Achieves a Resolution about One-Fourth of theWavelength Phys. Rev. Lett. 111, 243904 (2013). pdf