If a light wave is reflected by a moving object, the speed of the moving object can be determined from the measured frequency shift. The following applies approximately:

∆f: Frequency shift

∆f = 2· v/λ v: Velocity of the measured object

λ: Wavelength of the laser (e.g. 633nm for HeNe)

The frequency shift can be determined using interferometry. The intensity distribution created by superimposing the measurement and reference beams is used to determine the movement information of the object by demodulation.

The 1D differential vibrometer uses a second measuring head as a reference laser. Thus, the measuring signal describes the relative movements of the two measuring points to each other. This allows, for example, to measure the vibration behavior of individual components on a larger structure independently of superimposed (interference) vibrations.

Furthermore, the advantage of the differential vibrometer results from the absolute phase fidelity, as the difference between the two signals is already formed in the optical path.

By combining 3 individual laser vibrometers, it is possible to measure the vibrations in all three spatial axes at one measuring point. To do this, the vibrometers are aligned so that the three laser beams overlap in a cone shape at one point, the measuring point. Simple trigonometry can thus be used to determine the speeds of the three spatial axes at the measuring point of the object. If these three vibrometers with a fixed cone angle are accommodated in one measuring head, you have a very easy-to-use 3D laser vibrometer that is quick and convenient to operate.

The 3D laser scanning vibrometer consists of three independent 1D laser vibrometers, each of whose measuring heads has an adjustable mirror unit. This allows previously defined measuring points to be approached and measured. The movement of the surface of entire structures can thus be recorded automatically. The name already suggests that the three vibrometers can be used not only individually but also together to record measuring points in three dimensions. In addition to the spectral presentation of the vibration response, it also has the advantage of visualizing the vibration (mode) shapes. It makes it easy and uncomplicated to compare mode shapes with corresponding models.