Laser Vibrometry

General functional principle

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.

We use the following laser vibrometers for our vibration tests:

1D differential vibrometer

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.

3D vibrometer

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.