Digital holography

General

Measuring three-dimensional surfaces is a familiar task in industrial measuring technology. It typically employs optical methods such as fringe projection, laser triangulation and white-light interferometry. However, such systems may be either too slow or too coarse for the measuring tasks involved in in-line inspection. This new HoloTop inspection system from BMT offers a high measurement speed and accuracy by employing the digital holographic method.

Digital holography – non-contact and very accurate

holo-en-1HoloTop is a non-scanning method providing nevertheless a large measurement area.
An expanded laser beam illuminates the surface under investigation and is superimposed with the original laser beam upon reflection. The interference beam thus created contains all the necessary 3D information from the illuminated surface. This procedure is known as holography.

How can the 3D information concealed in the hologram be retrieved?

holo-en-2Superimposing the object beam with a reference beam and imaging the result onto a CCD chip produces a digital hologram. Digital reconstruction procedures of the spatial distribution of amplitude and phase can then be used to extract the 3D information from this hologram.
This two-stage process (phase-shift procedure in combination with evaluation of the diffraction integral) suppresses artifacts by a so-called »twin-image« and the zero diffraction order, which would otherwise be included in the reconstruction. In a last computing step, the synthetic wavelength generated by the two individual wavelengths is generated »virtually« in the computer. The synthetic phase map generated in this process contains the desired 3D information of the object being measured. This results in a 3D mapping of the object’s surface.

Many applications for this fast and flexible new measurement method

Of course, it is ultimately not the measuring techniques which is of intrest for the user but the benefits he gains from a measurement procedure.
The lateral resolution of this method is approx. 20 µm, the vertical resolution below 1 µm. This unique combination of a short measuring time and high resolution with a measuring field of up to 4 x 4 cm² in size makes HoloToP suitable for many tasks in especially for in-line applications.
Both the lateral resolution and the measuring area size can be customised. The impressive feature of the underlying technique of digital holography is it’s high tolerance to slightly reflective or rough surfaces. When being vibration-isolated properly an easy integration in a usual production environment is possible.

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Product sheet

Product sheet: Digital-holography.pdf

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