The Laser Source

The choice of the laser source has a major impact on the performance of a laser Doppler vibrometer (LDV). Eye-safety also is of great importance in a typical working environment. OptoMET laser Doppler vibrometers utilize cutting-edge SWIR technology or traditional HeNe laser sources.

Helium-Neon laser

The Helium-Neon (HeNe) laser operates at a wavelength of 632.8 nm. The red measurement beam is visible to the naked eye and can be positioned without additional aid.  HeNe lasers can be focused to a very small spot for the measurement of microstructures. Due to the negligible absorption it is possible to measure through water.

The output power of the HeNe laser is limited to 1 mW, in order to achieve class 2 eye safety. HeNe-based LDV are therefore routinely used when the surface of the measurement object reflects enough light to produce sufficient signal quality.

The HeNe laser emits more than one longitudinal mode: Wave trains with close frequencies overlap and form a beat signal. As a consequence the intensity, and hence the signal quality, becomes dependent on the working distance.
 

Infrared vibrometry

OptoMET pioneered SWIR (Short Wave Infrared) laser technology for optimum signal quality in challenging measurement tasks. Positioning the invisible laser spot is done with the help of a green, coaxially guided targeting laser.

At a wavelength of 1,550 nm, an output power of 10 mW is available for measurements while having the safest eye-safety classification of Class 1.  Water in the human eye absorbs the 1550nm laser power before it can cause damage. In combination with the threefold sensitivity of SWIR photodetectors compared to the HeNe visible light regime, this creates the basis for superior signal quality in nearly all vibration measurement tasks, regardless of the working distance.

Not only dark, non-smooth or other surfaces with poor reflectivity but also measurements over large distances are the uncontested domain of SWIR vibrometry. Excellent temperature stability and a long laser life time offer added value in using SWIR technology.
 

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