Uni-Potsdam Physik - Uni-Potsdam
Photonik - Physik - Uni-Potsdam

Broadband laser

Light source for the coherence radar

The coherence radar allows the contactless measurement of three dimensional object surfaces with a lateral resolution of some microns. Applications are mainly located in mechanical and electrical engineering, but can also be found in medicine and cosmetics.

Fig. 1 Scheme of the coherence radar

In our working group we investigate within the third-party funds "Grundlagen breitbandiger Kurzpulslaser für die Interferometrie" (FESMET) (funded by BMBF and VDI) broadband radiation sources, in particular broadband emitting lasers.

Large objects with weakly reflecting surfaces require a high illumination intensity which can only provide by laser light sources. On the other hand a laser generally radiates light with a spectrally small bandwidth. The task is to design a light source that emits radiation with a short coherence length (i.e. small temporal coherence) and simultaneous a good beam quality (i.e. high spatial coherence). The coherence length is via the uncertainty relation linked to the spectral width of the light source: the broader the spectrum the shorter is the coherence length. By shortening the coherence length of the light the longitudinal resolution can be increased up to the surface roughness of the object.

The light source for the coherence radar should emit in the visible spectral range with 200-300 mW average output power in transversal fundamental mode (TEM00). For that purpose several designs with gain switched Ti:sapphire laser or Cr:YAG laser has been investigated. For smaller applications we designed broadband light sources based on anti-reflecting coated diode lasers.

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Fig. 2 Broadband laser labor