Herve Rigneault

Dipole radiation into grating structures

We present a detailed electromagnetic analysis for the radiation of an electric source located inside grating structures. Our analysis is based on the differential method and uses the scattering-matrix algorithm. We show that gratings that exhibit periodic modulations along two spatial directions (crossed gratings) enable one to couple out the totality of the light emitted by the source into the guided modes of the structure. This property is investigated through the computation of the far-field radiation patterns for crossed gratings with various etching depths. One key result is the possibility to confine the emitted light in a direction about the sample normal, a property that is of interest in the context of spontaneous emission control by microcavity structures.

Spontaneous emission into planar multi-dielectric microcavities: Theoretical and experimental analysis of rare earth ion radiations

Abstract Spontaneous emission control for rare earth ions implanted inside planar multidielectric microcavities is investigated theoretically and experimentally. Rigorous classical electrodynamics analyses are presented and compared in order to compute the electromagnetic power provided by sources located inside planar dielectric multilayer structures. Radiation patterns and lifetime measurements are performed in Ta 2 O 5 /SiO 2 microcavities implanted with erbium and praseodymium ions. Although we demonstrate a significant enhancement of the spontaneous emission in a direction normal to the layer (up to 30%), we show that a large amount of the emitted power is carried by the guided modes of the structures.

Spontaneous Emission Control with Planar Dielectric Structures: An Asset for Ultrasensitive Fluorescence Analysis

We report on the interest of spontaneous emission control with planar dielectric multi-layer structures to increase the fluorescence collection efficiency in single-molecule detection experiments and ultrasensitive analysis. The effect of a very simple Fabry Perot microcavity on the radiation pattern of Eu3+ chelate molecules is introduced and discussed. Then the fluorescence correlation spectroscopy (FCS) technique is used to detect Cyanine 5 molecules on a simple mirror and Rhodamine 6G (R6G) molecules in a microcavity, both in liquid solutions. The respective advantages of those dielectric structures for increasing the count rate per molecule are described. The detection enhancement is used to demonstrate photon antibunching on the nanosecond time scale with a dilute solution of R6G molecules (10-9 M) in the microcavity.

Guided-wave characterization techniques for the comparison of properties of different optical coatings

The specific behavior of optical thin films very often leads to limitations of optical system performance. Accurate characterization techniques for evaluating film properties are necessary to understand this behavior. Characterization techniques based on the propagation of guided waves in the thickness of the films appear to be very useful. We report our particular way to determine the refractive index and the thickness of both isotropic and anisotropic thin films. Guided-waves techniques are sensitive enough to detect slight variations of thin film optical constants, so we use them to study the variations of refractive index versus temperature. From this we can obtain the thermorefractive coefficients ∂ n /∂ T of our layers. Moreover, we can obtain, in some cases, the nonlinear refractive index coefficient. We also measure guided-wave attenuation and laser damage threshold with a digital imaging system. nThese means, dependent on guided waves, are used in combination for a comparative analysis of TiO 2 and Ta 2 O 5 layers made by different eposition techniques (conventional evaporation, ion assisted deposition and ion plating).

Praseodymium-doped planar multidielectric microcavities: induced lifetime changes over the emission spectrum

We study lifetime modifications induced by luminescent microcavities in the case of praseodymium-doped planar Ta2O5–SiO2 multidielectric structures. From the experimental point of view we measure different decay times of the 1D2 excited level for different wavelengths in the inhomogeneous praseodymium emission spectrum. Decay times depend on the spectral detuning between considered ions and the cavity, and we observe significant changes around the resonance wavelength of the microcavity. The decay times are explained with an electromagnetic modal analysis of spontaneous emission developed in the case of less-loss microcavities.

Light emission from europium chelates located in crossed grating structures

We investigate experimentally the emission of luminescent molecules located in corrugated waveguides. Both shallow and deep gratings are considered and comparison with a simple slab waveguide is discussed, in terms of extracted power. The key result is the demonstration that a corrugated waveguide allows one to couple out the guided mode power into arc-shaped paths which can be close to the sample normal. We believe that this type of structure is of interest in, for example, LED and single-photon-source applications.

Strong extraction coefficient for sources located inside waveguide grating structures

An electromagnetic theory for sources radiating into crossed waveguide gratings is presented and implemented numerically. In the framework of spontaneous emission control, we present a structure which can couple out the total guided-mode power emitted by a point source dipole located in the corrugated region. Numerical calculations show that most of the total emitted light is confined in specific arc shape directions.

Spontaneous emission in multilayer microcavities: modal theory extended with Fourier-Green analysis for dissipative structures

Two rigorous theories are presented and compared to describe the interaction with the electromagnetic field of localized sources confined within microcavities. Both the light which can escape the structure and the embedded radiation are taken into account by these formalisms. The modal theory describes the field in terms of modal functions and is limited to lossless structures. On the other hand, the Green approach can naturally cope with lossy cavities and considers the coupling of the sources with a continuum of waves with spatial frequencies ranging from zero to infinity. The two theories are compared and the consequences of losses are investigated in the case of a current source located in the spacer of a resonant multilayer structure. It is shown that the modal theory gives correct predictions when the imaginary part of the refractive index is as large as , whereas the Green approach becomes necessary to describe the emission in lossy structures. In this last case, we show that the spontaneous emission factor is not strongly affected by losses, although the emitted power is decreased due to absorption.

Mechanical properties of dielectric thin films

Stress in thin films deposited by Reactive Low-Voltage Ion Plating is studied in air and at room temperature. A multilayer stack, composed of tantalum pentoxide and silicon dioxide layers, is considered and the interactions layer to layer turn out to have no effect as regards to the final bending. Evolution in stress after annealing shows the possibility to reduce the stress as well as the absorption for tantalum pentoxide thin films. Finally, ion implementation, such as helium and xenon, at high energy, prove to be also a way to vary and diminish the stress in thin films.

Stress in dielectric thin films : Evolution with annealing and ion implantation

Stress in dense thin films deposited by Reactive Low-Voltage Ion Plating or by Ion Assisted Deposition is investigated in air and at room temperature. Ion implantation, at high energy, proves to be a way to vary and diminish the stress in thin films. Stress changes with annealing show the possibility to reducing not only stress but also optical absorption.