Beam expander module
For LDV measurements, the size of the measurement volume depends on the beam spacing, the beam diameter and the focal length of the LDV probe optics. Typically, equipping a standard LDV probe such as the fp50 shift with long focal length front optics (e.g. f=800 mm) results in a measurement volume length of approx. 10 mm. This is often not small enough to achieve high spatial resolution in velocity measurements.
The combination of the standard LDV probe optics fp50 shift with a beam expander leads to a significant shortening of the measuring volume. With a focal length of 800 mm, the length of the measuring volume can be reduced by more than 50 % to 4 mm. Furthermore, the smaller size of the measuring volume leads to a higher illumination density in the measuring volume. This means higher signal quality and a higher data rate.
The beam expander uses a Galilean telescope design. The beam spacing is extended from 45 mm to 70 mm. The focal length of the front lens can be adjusted by the spacing of the lenses inside the beam expander. The beam expander module is mounted directly on the fp50 shift probe.