The 3D Laser ESPI System (laser holography) measures in and out-of-plane displacements and strain very precisely using laser interferometry. It is used in a broad variety of applications from fatigue tests to general strain measurement and analysis. The interferometric method ESPI is well suited to measure the smallest 3D displacements and plane strain with resolutions of approximately 10 nanometers or 1 micrometer per meter.
The ESPI system includes a high quality digital CCD camera with computer-controlled shutter time, one or multiple laser sources, a computer controlled phase shift device, the needed optic and the needed electronic driver and the data acquisition and treatment system, integrated in the PC. The laser light is directed onto the object under test and the camera grabs the resulting speckled image. Object deformations in the sub-micrometers range modify the image gathered by the CCD camera. Using appropriate image treatment, the difference between the two images shows up with black interference fringes (real time viewing of the actual deformation).
Common uses include:
- Deflection, strain, thermal expansion and residual stress measurements - FEA validation - Determining the linear behavior, even of brittle materials - Characterizing heterogeneous materials - Characterizing the transition range of two different materials - Quality control of honeycomb and sandwich structures