Dieter M. Profunser
École Polytechnique Fédérale de Lausanne
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Dieter M. Profunser.
Ultrasonics | 2002
Jacqueline Vollmann; Dieter M. Profunser; Jurg Dual
This investigation deals with various new aspects of the sensitivity improvement of a pump-probe laser based acoustic method. A short laser pulse is used to excite a mechanical pulse thermo-elastically. Echoes of these mechanical pulses reaching the surface are causing a slight change of the optical reflectivity. The surface reflectivity is scanned versus time with a probe pulse. Thus the time of flight of the acoustic pulse is measured. The quantity to be measured i.e. the optical reflectivity change deltaR caused by acoustic pulses, is rather small. A set-up having an estimated sensitivity deltaR/R of about 10(-5) has shown to be sufficient to detect up to the fifth echo in a 50 nm aluminum film on sapphire substrate. A key challenge is the reduction of optical and electrical cross-talk between the excitation and the detection. Therefore the concepts of double-frequency modulation, cross-polarization, and balanced photodetection are implemented. Practical aspects like beam guiding, modulation techniques, beam focus minimization, and beam focus matching are discussed. Measurements for single- and multi-layer metallic films demanding higher sensitivity are presented.
Scientific Reports | 2013
Paul H. Otsuka; K. Nanri; Osamu Matsuda; Motonobu Tomoda; Dieter M. Profunser; Istvan A. Veres; Sorasak Danworaphong; Abdelkrim Khelif; Sarah Benchabane; Vincent Laude; Oliver B. Wright
Control of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides. However, frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling. Using a wide range of wavevectors k, we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real- and k-space in two spatial dimensions, thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates. Such use of k-t space is a first in acoustics, and should have other interesting applications such as acoustic-metamaterial characterization.
Applied Physics Letters | 2008
Takashi Fujikura; Osamu Matsuda; Dieter M. Profunser; Oliver B. Wright; Jeremy Masson; Sylvain Ballandras
Time resolved images of acoustic waves in the 100 MHz–2.2 GHz range are obtained for an electrically excited thin-film bulk acoustic wave resonator by means of an ultrafast optical technique. Electrical pulses, synchronized to ultrashort laser pulses, piezoelectrically excite the device, and synchronous near-infrared laser pulses interferometrically detect surface motion. The frequency dispersion is extracted using spatiotemporal Fourier transforms, revealing both longitudinal and surface acoustic modes.
New Journal of Physics | 2012
Istvan A. Veres; Dieter M. Profunser; A. A. Maznev; A. G. Every; Osamu Matsuda; Oliver B. Wright
We use locally-excited gigahertz surface phonon wavepackets in microscopic line structures of different pitches to reveal profound anisotropy in the radiation pattern of a point source in a grating. Time-domain data obtained by an ultrafast optical imaging technique and by numerical simulations are Fourier transformed to obtain frequency-filtered real-space acousticfield patterns and k-space phononic band structure. The numerically-obtained k-space images are processed to reveal an intriguing double-horn structure in the lowest-order group-velocity surface, which explains the observed non-propagation sectors bounded by caustics, noted at frequencies above the bottom of the first stop band. We account for these phonon-focusing effects, analogous to collimation effects previously observed in two- and three-dimensional lattices, with a simple
Nondestructive Evaluation and Reliability of Micro- and Nanomaterial Systems | 2002
Dieter M. Profunser; Jacqueline Vollmann; J. Bryner; Jurg Dual
Optical techniques for monitoring acoustic waves excited in thin films or micro-structures with ultrashort laser pulses are useful for the accurate and nondestructive evaluation as well as for the characterization of material properties. The pump-probe laser-based acoustic methods generate acoustic bulk waves in a thermo-elastic way by absorbing the pump laser pulses at the surface of the thin film. The acoustic waves are partly reflected at the interface of thin film and substrate. Back at the film surface the reflected acoustic wave causes a change of the optical reflection coefficient, which is measured by the probe laser pulse. One-dimensional, thermo-elastic models are developed to investigate the laser-based excitation and propagation of the longitudinal acoustic pulses in thin aluminium films. The change of the optical reflection coefficient is governed by the temperature distribution and the mechanical strain caused by the traveling acoustic pulse. The presented comparison of the simulation results of thin aluminium films with the pump-probe-measurements allows to determine film thickness or Youngs modulus. Furthermore material properties like thermal conductivity and photoacoustic properties are estimated. The thermo-elastic modeling of the two-dimensional case and the resulting new possibility to use the pump-probe technique for the nondestructive evaluation of micro-structures is discussed. Further directions of the ongoing research project are presented.
Ultrasonics | 2000
D. Gsell; Dieter M. Profunser; Jurg Dual
To determine the dispersion relation, guided waves are excited in specimens over a broad frequency range. The surface displacements are measured over time and space. The recorded data are analysed using a quasi-three-dimensional spectrum estimation algorithm. In the time domain a fast Fourier transform is used to extract the frequencies. To obtain the wave numbers, in space a two-dimensional matrix-pencil approach is applied to the data set. Using a suitable constitutive model (transversely isotropic or orthotropic) dispersion curves are calculated. Good agreement was found between the experimental and the numerically calculated dispersion relations after adjusting the material parameters. Since the dispersion relation of a structure depends on the mechanical material properties frequency-dependent material parameters can be extracted from the above-mentioned relation between frequency and wave number.
Ultrasonics | 2002
Dieter M. Profunser; Jacqueline Vollmann; Jurg Dual
Pulsed laser acoustic experiments have the advantage of very high temporal resolution. However, the lateral resolution amounts to several wavelengths of light. To improve the lateral resolution a focussing tip in which the mechanical waves are focussed is introduced. The combination of high resolution in time and space domain leads to a new potential time resolved scanning probe method. Therefore several axi-symmetric structures are investigated numerically using a finite difference method. The ultrasonic wave propagation in different tips is discussed. By varying the geometry of the tip, the displacement at the sharp end is maximized. The numerically calculated results are verified experimentally on structures having macroscopic dimensions. Scaling effects are considered in order to translate the results into the microscopic scale where arbitrary geometries are much more challenging to implement.
internaltional ultrasonics symposium | 2002
Dieter M. Profunser; Jacqueline Vollmann; Jurg Dual
The measurement of bulk acoustic waves (BAW) excited in thin films or microstructures with ultrashort laser pulses is a powerful method for accurate and nondestructive evaluation of material or geometrical properties. Optical techniques like the pump-probe laser-based acoustic method generate BAW in a thermoelastic way by absorbing the pump laser pulses at the surface of the specimen. The acoustic waves are partly reflected at any discontinuity of the acoustic impedance. Back at the surface the reflected acoustic pulses cause changes of the optical reflection coefficient, which are measured with the probe laser pulses. The measurement technique is explained for the case of an aluminium thin film on sapphire. The influence of the film thickness and the deposition method of the thin films on the bulk wave speed is shown. In the second part of the paper this technique is used for measuring the bulk wave propagation in very thin membranes. The BAW propagation in freestanding silicon-nitride aluminium multilayer membranes with total thickness in the order of several hundred nanometers is measured. The measurements of the freestanding membranes are compared with measurements of the supported case. The technique presented in this paper can also be applied for the characterization of material or geometrical properties of thin film BAW resonators. The advantage of the method lies in its nondestructive and noncontact approach, which is necessary for ultrathin and brittle structures.
Proceedings of SPIE, the International Society for Optical Engineering | 2001
Jacqueline Vollmann; Dieter M. Profunser; Jurg Dual
This investigation deals with various new aspects of the sensitivity improvement of a pump-probe laser based acoustic method. A short laser pulse is used to excite a mechanical pulse thermo-elastically. Echoes of these mechanical pulses reaching the surface are causing a slight change of the optical reflectivity. The surface reflectivity is scanned versus time with a probe pulse. Thus the time of flight of the acoustic pulse is measured. The quantity to be measured i.e. the optical reflectivity change DR caused by acoustic pulses, is rather small. A set-up having an estimated sensitivity DR/R of about 10(superscript -5 has shown to be sufficient to detect up to the 5th echo in a 50 nm aluminum film on sapphire substrate. A key challenge is the reduction of optical and electrical cross talk between the excitation and the detection. Therefore the concepts of double-frequency modulation, cross-polarization, and balanced-photo-detection are implemented. Practical aspects like beam guiding, modulation techniques, beam focus-minimization, beam focus-matching, and the variation of the pump-probe power ratio are discussed. Measurements for single and multi-layer metallic films demanding higher sensitivity are presented.
Review of Scientific Instruments | 2003
Jacqueline Vollmann; Dieter M. Profunser; Jurg Dual
Free surfaces as well as interfaces between two neighboring materials are often subjected to diffusion processes like oxidation or migration of atoms. Such processes smooth out the difference of the acoustic impedances leading to microstructures having gradually varying mechanical properties like density and Young’s modulus. In the one-dimensional case of a metallic thin-film multilayer, the speed of sound becomes a function of the spatial thickness variable. Depending on the ratio between the acoustic wave length and the thickness of the diffusion zone, bulk waves reaching the zone are either dominantly transmitted or dominantly reflected. Thus a continuum having a variable sound velocity can be considered as an acoustic filter. The partial differential wave equation is solved numerically for an assumed velocity-versus-propagation direction function and the results are discussed. A series of experimental results obtained by a pump–probe–laser-acoustic technique is presented. Mechanical waves are excited ...