Olivier Haeberlé

Focusing of light through a stratified medium: a practical approach for computing microscope point spread functions. Part I: Conventional microscopy

We propose a method for microscope point spread function computation in which both design and actual acquisition parameters are explicitly introduced in the integrals describing the electromagnetic field in the focal region. This model therefore combines the ease of use of the Gibson and Lanni scalar approach with the accuracy of the Torok and Varga method. We also compare some theoretical predictions of this model with those of a scalar model. In particular, the scalar model underestimates the point spread function size. This has practical application, for example when deconvolving microscope images or analyzing point spread functions. The method may also be used for confocal microscopy.

Acoustical properties of irregular and fractal cavities

Acoustical properties of irregular cavities described by fractal shapes are investigated numerically. Geometrical irregularity has three effects. First, the low-frequency modal density is enhanced. Second, many of the modes are found to be localized at the cavity boundary. Third, the acoustical losses, computed in a boundary layer approximation, are increased proportionally to the perimeter area of the resonator and a mathematical fractal cavity should be infinitely damped. We show that localization contributes to increase the losses. The same considerations should apply to acoustical waveguides with irregular cross section.

Observation of vibrational modes of irregular drums

Vibrational modes of irregular or prefractal drums have been calculated using a correspondence between the wave propagation and the diffusion equations. The resonance frequencies and the vibrational-mode structures measured on low thickness plastic film membranes using a holographic setup are found to be in good agreement with theoretical predictions.

Identification of acquisition parameters from the point spread function of a fluorescence microscope

Except for blind methods, deconvolution of 3-D data sets acquired from a fluorescence microscope requires the knowledge of the point spread (PSF) of the instrument. Unsing the XCOSM package, we show first with simulations and then with recorded data that it is possible to recover from an experimental PSF some parameters, which are very difficult or impossible to measure during the acquisition, like the specimen depth or the immersion medium refractive index. Doing so, we can precise the acquisition protocol, which helps to use the instrument under optimal conditions. Furthermore, the knowledge of the actual acquisition condtions permits to use fo the deconvolution process a computed PSF, which is noiseless and as close as possible to the actual PSF. This helps to reduce errors in quantitative measurements after deconvolution, as shown with computations.

Polarized confocal theta microscopy

We propose a comprehensive treatment of theta microscopy based on dipole emission, which better describes fluorescence emission than the isotropic emission model, as fluorescence emission is often polarized. Formulas describing the point spread function for polarized confocal fluorescence theta microscopy are given. Examples are given and some advantages of polarized theta fluorescence microscopy are presented.

The improved point matching method for triangular metal gratings

Abstract In this paper, we present the “point matching method” (PMM) adapted for the calculation of Smith–Purcell (SP) radiation parameters in H-polarization, generated by relativistic electron beams (REB) passing close to a triangular metal grating. A truncated expression Hdy,n(N;β,ω) was used in order to find the coefficients Hdy,n(β,ω) in the infinite Rayleigh expansion of the diffracted field of a moving electron. A linear system of 2N+1 equations was solved, increasing the number N of harmonics until convergence solutions were achieved. When N→∞ then lim N→∞ H d y,n (N;β,ω)=H d y,n (β,ω) and the diffracted field can be calculated. SP radiation factors were calculated using the modified PMM for electron energies in 1–30 MeV domain and metal gratings with period length in 1–10 mm range.

Fluorescence microscopy with 3D resolution in the 100 nm range

We propose a combination of 4Pi and Theta microscopies to improve the resolution of fluorescence microscopy by using six microscope objectives in a configuration we call Multiple Objective Microscopy (MOM). A resolution in the 100 nm range is obtained in the three dimensions using low numerical aperture, long working distance objectives. The obtained results not only show that high resolution is not restricted to high numerical aperture objectives, but also open the possibility of exploring large volumes with a very good resolution.

Reciprocity theorem for Smith-Purcell radiation

Abstract Smith-Purcell radiation is produced when a charged particle moves close and parallel to a diffraction grating. Calculation of Smith-Purcell spectra is therefore linked to a special grating problem, involving incident evanescent waves describing the field of the moving electron. For large period gratings, radiation in the far-infrared and millimetric range is produced, in a spectral range where metallic gratings can often be considered as infinitely conducting. In that case, conservation laws and a reciprocity theorem are derived for Smith-Purcell radiation by applying techniques from electromagnetic grating theory.