Nicolas Bonod

Resonant optical transmission through thin metallic films with and without holes

Using a rigorous electromagnetic analysis of two-dimensional (or crossed) gratings, we account, in a first step, for the enhanced transmission of a sub-wavelength hole array pierced inside a metallic film, when plasmons are simultaneously excited at both interfaces of the film. Replacing the hole array by a continuous metallic film, we then show that resonant extraordinary transmission can still occur, provided the film is modulated. The modulation may be produced in both a one-dimensional and a two dimensional geometry either by periodic surface deformation or by adding an array of high index pillars. Transmittivity higher than 80% is found when surface plasmons are excited at both interfaces, in a symmetric configuration.

Effect of electric field on laser induced damage threshold of multilayer dielectric gratings

This paper studies gratings engraved in multilayer dielectric stacks for ultra high intensity laser compressors application. We design various grating profiles with high reflected efficiencies for 1780 l/mm multilayer dielectric gratings (MLD). Each grating is defined to exhibit a different electric field maximum value in the pillars of the grating. A damage testing facility operating at 1.053 mum, 500 fs pulse duration is used to damage test the parts manufactured from these designs. It is evidenced that for fixed incident angle and materials the damage of the grating is directly related to the electric field intensity maximum in the material, which depends on the groove profile. Laser induced damage thresholds of 5 J/ cm(2) are experimentally reached with very high and uniform efficiencies.

Mixed metal dielectric gratings for pulse compression

We report on manufacturing and testing results of high efficiency mixed metal dielectric gratings (MMLD) for high power pulse compression applications. The gratings with 1780 l/mm are etched in the top low index layer of a Au-(SiO2/HfO2)4-SiO2 mirror stack. Various grating profiles manufactured in order to modify the near electric field distribution are damage tested on a facility operating at 1.053 µm, 500 fs pulse duration. We evidence that damage threshold is governed by the value of the maximum electric field intensity inside the grating pillar. Moreover thresholds close to 3 J/cm2 beam normal are obtained with this new MMLD grating being thus an interesting alternative to gold and pure dielectric gratings for pulse compression applications.

Efficient excitation and collection of single- molecule fluorescence close to a dielectric microsphere

Dielectric microspheres illuminated by a tightly focused Gaussian beam can focus light on a tiny spot with subwavelength dimensions along the three directions of space. We report here a detailed experimental and theoretical study of the interaction between a single fluorescent molecule and this peculiar electromagnetic distribution. The microsphere increases the excitation intensity sensed by the molecule up to a factor of 2.2, while at the same time it allows for a collection efficiency of up to 60% by redirecting the light emitted at large incidences toward the optical axis. By combining these two effects, the number of collected fluorescence photons can be increased up to a factor of 5. We quantify the evolution of the excitation and collection contributions with the microsphere dimensions and compare our experimental findings with numerical simulations.

Differential theory: application to highly conducting gratings

The recently developed fast Fourier factorization method, which has greatly improved the application range of the differential theory of gratings, suffers from numerical instability when applied to metallic gratings with very low losses. This occurs when the real part of the refractive index is small, in particular, smaller than 0.1-0.2, for example, when silver and gold gratings are analyzed in the infrared region. This failure can be attributed to Lis inverse rule [L. Li, J. Opt. Soc. Am. A 13, 1870 (1996)] as shown by studying the condition number of matrices that have to be inverted. Two ways of overcoming the difficulty are explored: first, an additional truncation of the matrices containing the coefficients of the differential system, which reduces the numerical problems in some cases, and second, an introduction of lossier material inside the bulk, thus leaving only a thin layer of the highly conducting metal. If the layer is sufficiently thick, this does not change the optical properties of the system but significantly improves the convergence of the differential theory, including the rigorous coupled-wave method, for various types of grating profiles.

Differential theory of diffraction by finite cylindrical objects.

We present a differential theory for solving Maxwell equations in cylindrical coordinates, projecting them onto a Fourier-Bessel basis. Numerical calculations require the truncation of that basis, so that correct rules of factorization have to be used. The convergence of the method is studied for different cases of dielectric and metallic cylinders of finite length. Applications of such a method are presented, with a special emphasis on the near-field map inside a hole pierced in a plane metallic film.

Structured Surfaces as Optical Metamaterials: Physics of extraordinary transmission through subwavelength hole arrays

Optical metamaterials are an exciting new field in optical science. A rapidly developing class of these metamaterials are those that allow the manipulation of volume and surface electromagnetic waves in desirable ways by suitably structuring the surfaces they interact with. They have applications in a variety of fields, such as materials science, photovoltaic technology, imaging and lensing, beam shaping, and lasing. Describing techniques and applications, this book is ideal for researchers and professionals working in metamaterials and plasmonics, as well as those just entering this exciting new field. It surveys different types of structured surfaces, their design and fabrication, their unusual optical properties, recent experimental observations, and their applications. Each chapter is written by an expert in that area, giving the reader an up-to-date overview of the subject. Both the experimental and theoretical aspects of each topic are presented.

Pulse compression gratings for the PETAL project: a review of various technologies

A Petawatt facility called PETAL (PETawatt Aquitaine Laser) is under development near the LIL (Ligne dIntegration Laser) at CEA Cesta, France. PETAL facility uses chirped pulse amplification (CPA) technique. We herein review various studies made to develop pulse compression gratings for CPA application with high laser induced damaged threshold. Different multilayer dielectric (MLD) gratings have been manufactured to exhibit different electric field maximum values in the pillars of the grating. A damage testing facility operating at 1.053μm, 500fs pulse duration is used to damage test the parts manufactured from these designs. It is evidenced that for fixed incidence and materials the damage of the grating is directly related to the electric field intensity maximum in the material, which depends on the groove profile. Laser induced damage thresholds of 5 J/ cm2 is experimentally reached with very high and uniform efficiencies. New structures are currently under study, gratings with mixed metal/dielectric layers MLD or more exotic 2D and 3D photonic crystals devices. For each case, we detail the design and expected performances. We also give some diffraction efficiency and laser damage measurements when samples were manufactured.

Mixed metal dielectric gratings for pulse compression applications

A Petawatt facility called PETAL (PETawatt Aquitaine Laser) is under development near the LIL (Ligne dIntegration Laser) at CEA Cesta, France. PETAL facility uses chirped pulse amplification (CPA) technique [1]. This system needs large pulse compression gratings exhibiting damage threshold of more than 4 J/cm2 beam normal at 1.053μm and for 500fs pulses. In this paper, we study an alternative design to the classic Multidielectric (MLD) gratings [2] called mixed metal-multidielectric grating (MMLD). In this design, the dielectric mirror stack of the MLD grating is replaced by a gold reflective layer covered with a few pairs of HfO2/SiO2 [3]. The number of pairs must be high enough to ensure a sufficient reflection coefficient in order to prevent damage of the gold layer. On the top of the stack, a silica layer is coated to receive the grating. After some considerations on the grating design and optimization, a comparison between MLD and MMLD mirrors is also carried out. We finally detail the measured diffraction efficiencies obtained on MMLD gratings.

Recent progress in the development of pulse compression gratings

A Petawatt facility called PETAL (PETawatt Aquitaine Laser) is under development near the LMJ (Laser MegaJoule) at CEA Cesta, France. PETAL facility uses chirped pulse amplification (CPA) technique. This system needs large pulse compression gratings exhibiting damage threshold of more than 4 J/cm2 in normal beam at 1.053μm and for 500fs pulses. In this paper, we present our recent progress and developments of such pulse compression gratings. We have shown in previous works that the enhancement of the near electric field inside the pillars of the grating drives the damage threshold. This was evidenced from a macroscopic point of view by laser damage testing. We herein demonstrate that damage morphology during damage initiation at the scale of the grating groove is also consistent with this electric field dependence. Some recent grating designs will also be detailed.