Jean Paul Roger

Nomarski imaging interferometry to measure the displacement field of micro-electro-mechanical systems

We propose to use a Nomarski imaging interferometer to measure the out- of-plane displacement field of micro-electro-mechanical systems. It is shown that the measured optical phase arises from both height and slope gradients. By using four integrating buckets, a more efficient approach to unwrap the measured phase is presented, thus making the method well suited for highly curved objects. Slope and height effects are then decoupled by expanding the displacement field on a functions basis, and the inverse transformation is applied to get a displacement field from a measured optical phase map change with a mechanical loading. A measurement reproducibility of approximately 10 pm is achieved, and typical results are shown on a microcantilever under thermal actuation, thereby proving the ability of such a setup to provide a reliable full-field kinematic measurement without surface modification.

Analytical inversion of photothermal measurements: Independent determination of the thermal conductivity and diffusivity of a conductive layer deposited on an insulating substrate

The long distance behavior of the surface temperature wave in a thermoreflectance microscopy experiment is established for a conductive layer deposited on an insulating substrate. At large distance from the point source, heat is confined, so the amplitude decrease is lower than for a bulk sample. From the slopes which appear on the phase and on the log scale amplitude, a procedure is proposed to extract, separately, the thermal diffusivity and conductivity of the layer, taking into account data obtained at different modulation frequencies. Experimental results are presented which confirm the validity of the method.

Optical characterization of polycrystalline CuInSe2 films on scattering substrates by fourier transform photothermal deflection spectroscopy

Abstract Fourier transform photothermal deflection spectroscopy is used to obtain values for the optical band gaps of relatively rough polycrystalline films of CuInSe 2 on scattering Al 2 O 3 or Mo/Al 2 O 3 substrates and to estimate absorption coefficients at photon energies close to the band gap. Heating of the films in air generally caused a slight shift to lower photon energies of the band gap. Absorption edges in Cu 2 Se-rich films were absent or poorly resolved. Results obtained for a single-crystal sample agree well with literature values. In this case it was possible to determine from the variation in the phase angle of the signal with photon energy that the sub-band-gap absorption originated from the bulk rather than the surface. We did not find conclusive evidence for indirect transitions in either the crystal or the thin films. The integration of this method into a semiconductor-liquid junction system for semiconductor characterization is discussed. In order to illustrate this possibility, simultaneous photothermal deflection and photocurrent measurements are performed for the single crystal and for a thin film immersed in an electrolyte.

Micron scale photothermal imaging

Abstract In this paper, we present various experimental results which demonstrate the ability of photothermal methods to perform heat diffusion imaging at the micron scale. Photoreflectance microscopy measurements have been performed on a composite sample presenting a strong anisotropy of thermal properties and on microelectronic devices. We will then introduce the CCD array photothermal microscopy which permits the acquisition of a complete image in a single shot, without moving the sample. A stroboscopic technique must be used in order to adjust to the relatively low frame rate of the CCD camera. We will discuss two cases: homodyne and heterodyne detection.

In Situ, Real Time Monitoring of Surface Transformation: Ellipsometric Microscopy Imaging of Electrografting at Microstructured Gold Surfaces

Surface chemical reactivity is imaged by combining electrochemical activation of a surface transformation process with spatiotemporal ellipsometric microscopy. An imaging ellipsometric microscope is built, allowing ellipsometric images of surfaces with a lateral resolution of ∼1 μm and a thickness sensitivity of ∼0.1 nm in air and 0.4 nm in a liquid. These performances are particularly adapted for using such optical setup as an in situ, real time chemical microscope to observe a chemical surface transformation. This microscope is tested for the monitoring of the electrochemically actuated diazonium grafting of a gold surface. Such reaction is a model system of organic material deposition on a gold surface induced by an electrochemical actuation. Using either plain or physically or chemically structured electrodes, it allows for the characterization of local phenomena associated with the electrografting process. This illustrates its potential to reveal the local (electro)chemical reactivity of surfaces.

Achromatic damage investigations on mirrors for UV-free electron lasers

Storage Ring Free Electron Laser (FEL) are attractive, full of promise, tuneable and powerful laser sources for the UV range. High reflectivity dielectric mirrors should be produced in order to allow lasing at very short wavelength, with a long stability in a strongly harsh environment and to optimize the extracted FEL power required for most of the newest applications. The front mirror of the laser cavity receives all the synchrotron radiation (SR) emitted by the wiggler, which is responsible for the mirror degradation, combined with the contamination by the vacuum residuals. We are tackling the problem of tests and manufactures of reliable robust mirrors and explore themes such as resistance analysis of UV mirrors to FEL multiscale power, broadband (X-UV) mirror robustness. Under drastic SR conditions, multiscale wavelength damages could be observed. Specific measurement techniques, able to investigate localized spatial modification induced by the non-uniform synchrotron radiation are presented. A local crystalline structure modification of the high index material appears together with a severe increase of the roughness.

Multiscale Degradations of Storage Ring FEL Optics

The advanced understanding of the complete degradation phenomena is crucial in order to develop robust optics for FEL. Under very harsh Synchrotron Radiation conditions, results show that multiscale wavelength damages could be observed, inducing local crystalline structure modifications of the high optical index material with a severe increase of the surface roughness.

Toward resistant UV mirrors at 200 nm for free electron lasers: manufacture, characterizations, and degradation tests

Storage Ring Free Electron Laser are attractive and full of promise tunable and powerful laser sources for the UV range. Concerning the optical cavity, the relatively small gain obtained in the UV calls for the necessity to use high reflectivity multilayer mirrors with reliable longevity in synchrotron environment. It is also crucial to limit their absorption in order to optimize the extracted power required for most of the applications. Indeed, the front mirror of the laser cavity receives not only the first harmonic where the lasers operates but all the synchrotron radiation emitted by the undulator: a wide spectrum extending towards X rays. These short wavelengths are responsible for the mirror degradation which results from changes in the coating materials (high induced absorption, color centers, heating...) as well as from carbon contamination due to cracked hydrocarbons originating from the residual vacuum atmosphere. Deposition technologies which allow the manufacture of very dense oxide coatings with low absorption and high reflectivity in UV spectral region were optimized and characterized for this purpose. We report here degradation studies performed on UV mirrors for Storage Ring Free Electron Lasers down to wavelengths as short as 200 nm.

Optical and thermal characterization of coatings

Abstract The mechanical, thermal and optical properties of thin coatings have been considerably improved these last years. For instance optical coatings for laser mirrors with sub ppm losses are now available. Moreover thermal diffusivity varying over more than 4 orders of magnitude can be found when going from polymers coatings to diamond ones. Reliable sensitive techniques are necessary to characterize them. First, we present two optical techniques: ellipsometry and polarization microscopy which lead to determination of optical (refractive index) and geometrical (thickness, homogeneity) parameters. Second, we describe a few optically based photothermal techniques in which heating and detection are contactless and non-destructive: photothermal microscopy, mirage detection, time resolved ellipsometry, etc. These techniques allow local (down to micron scale) to global determination of the optical properties (absorption with a few ppb sensitivity) as well as thermal properties (diffusivity, effusivity) and reveal inhomogeneities, adhesion as well as anisotropies.

Spectroscopic ellipsometry under external excitation

Abstract This contribution presents a new kind of spectroscopic ellipsometry under modulated or pulsed external excitation when the sample physical properties (such as the refractive indices or thicknesses, e.g. in a layered structure) can be changed by the absorption of the incident energy. These photoinduced variations are detected through the ellipsometric signals. The experimental procedure used is first to fix the azimuth of polarizer, next successively to set the azimuth of analyser at four positions with an interval of 45°, then to measure the static signal and the photoinduced signal and finally to determine the ellipsometric parameters tan ψ and cos Δ, and their variations d(tan ψ) and d(cos Δ). So that the d(tan ψ) and d(cos Δ) can be recorded as a function of time or frequency, the time resolution is as fast as a few nanoseconds (limited by our laser pulse duration). Minimum variations in the ellipsometric parameters d(tan ψ) and d(cos Δ) of the order of 10−5 under modulated excitation, and 10−6 under pulsed excitation have been measured. This new technique has been applied to bulk and implanted semiconductors; dynamic indices and various heat diffusion processes can be observed from the stimulated spectroscopic ellipsometry.