Photoacoustic and photothermal material research
- Laser ultrasonics - photoacoustic and photothermal investigation of heterogeneous materials and structures
- Photoacoustic and photothermal investigation of soft matter
- Photoacoustic and photothermal research of nano-scale structures
- Current research
- Keywords
Laser ultrasonics - photoacoustic and photothermal investigation of heterogeneous materials and structures
Laser excited acoustic and thermal waves have the interesting property that they can deliver information about material properties on locations which are inaccessible for other techniques. In this research we study reflection, transmission, diffraction and nonlinear effects of thermal and elastic waves from the sub-Hz till GHz range using heterodyne diffraction, stroboscopic interferometric imaging, IR thermography and advanced data processing techniques (Gabor transformation, neural network recognition). In this way, in a non-contact way, it is possible, besides the elastic characterization of materials, to determine their depth sturcture, and to detect and identify sub-surface defects.
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Photoacoustic and photothermal investigation of soft matter
The transition from a liquid to a solid state of matter sometimes goes along with a colorfull and complex pallet of physical properties, which leads to interesting technological applications. Molecules in liquid crystalline compounds (LCD-displays) are aligning or show a liquid-like layered structure. Supercooled liquids (polymers, heat storage materials, speed-dependent mechanical coupling fluids) behave solid-like or liquid-like depending on the time scale of observation. Some materials (memory alloys) have a shape memory when cooling. In some gels the elastic wave velocity is extremely small, leading to spectacular effects. Using thermal, elastic and dielectric spectroscopy we study these strongly frequency and temperature dependent thermo-elastic phenomena in the sub-Hz - GHz range. For this we use IR thermography, photopyroelectric spectroscopy, dielectric spectroscopy and laser heterodyne diffraction and optical interferometry.
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Current research
- Photothermal spectroscopy of thermal conductivity and specific heat capacity of binary liquid mixtures near phase transitions
- Photothermal depth profiling of pigment concentration in colored polymers
- Photothermal determination of thermal properties of colloidal systems
- Laser ultrasonic depth profiling of functional gradient materials
- Laser ultrasonic investigation of acoustic wave propagation at the interface between liquids and porous media
- Laser ultrasonic investigation of defects in plates
- Photothermal spectroscopy of thermal conductivity and specific heat capacity of glass forming liquids
- Photoacoustic heterodyne diffraction spectroscopy of longitudinal and transverse modulus of glass forming liquids
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Keywords
Material properties
- Elastic moduli: linear and nonlinear
- Thermal conductivity and heat capacity, thermal effusivity and diffusivity
- Optical absorption coefficient and refractive index
- Magnetic susceptibility and magnitization
- Dielectric permittivity
- Phase transitions
- Room acoustic properties
Materials
- Liquids
- Complex liquids
- Liquid crystals
- Thin coatings on substrates
- Multilayers
- Thin films
- Surface treated metals
- Insulating materials
- Carbon fiber composites
- Inhomogeneous materials with a thermal, elastic, electric, refractive index, optical absorption, lattice parameter depth profile
Experimental methods
- Laser ultrasonics
- Laser excitation: gaussian, periodic, sweep, random spatial patterns
- Piezo excitation: longitudinal, shear and interface waves
- Wave detection: vibrometer, Michelson/grating/Fabry Perot interferometer, PVDF wedge, heterodyne diffraction
- SAW imaging
- Photothermal spectroscopy
- Photoacoustic cell
- Mirage effect
- Photopyroelectric spectroscopy
- Infrared radiometry
- Interferometric thermal imaging
- Thermochromic thermal imaging
- Depth profiling
- Thermometry
- Interferometry
- Heterodyne diffraction
- Magnetocaloric effect
- Dielectric spectroscopy
- Acoustics
- Electronics
- Optics
- Lithography
- Temperature control
- Time and frequency domain signal generation and detection
- Ellipsometry
- Adiabatic scanning calorimetry
- Thermal conductivity measurements -160..60 Celcius
- Industrial insulating materials
- Liquids
- Solids
Analytical and numerical methods and software
- Surface Acoustic Waves in multilayers
- Lamb waves in films
- 3D thermal diffusion in multilayers
- Nonlinear fitting
- 2D Fourier transforms
- Neural network signal recognition
- Audio acoustic analysis
- Ellipsometry in multilayers
- Optical propagation in birefringent multilayers
- X-ray diffraction in multilayers
- Eddy currents in multilayers
- Time and frequency domain signal analysis
- Image and movie processing in spatial, time and frequency domain
- Inverse problems: depth profiling of
- Thermal properties (photothermal signal)
- Elastic properties (SAW dispersion)
- Refractive index (ellipsometry)
- Electrical conductivity (eddy current)
- Lattice parameter (X-ray diffraction)
- Optical absorption (photothermal signal)
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