The 2D-LDV Long Range Optic is designed for applications such as measurements in big wind tunnels or big pipes which need a longer-than-usual focal length to access the measurement area. Typically these applications require focal lengths in the region of 1000 mm and beyond. Using a standard LDV system, even when fitted with a beam expander, will lead to unacceptably elongated measurements volumes, 5-10mm or more, with the resultant effect of poor spatial resolution and poor signal quality due to reduced laser intensity.
ILA has developed a Long Range LDV Optic for these applications, with achievable focal lengths of 2 m and above.
The idea of the optical setup is to maximize the beam distance, in practice up to 400 mm. Of course such beam distances cannot be practically achieved with a single front lens. Instead each beam has its own collimation optics to focus the beam inside the measurement volume. The receiving optics is positioned in the middle of the beams and operates in backwards scattering mode. The received light is split into its different constituent wavelengths and coupled into multi-mode fibers linking into the photodetectors of an ILA LDV-Controller or, in the case above, into a BSA.
Both components are shifted with an integrated Bragg cell. The laser sources are two DPSS- Genesis 2W Lasers with 514nm and 488nm. They are coupled directly into the LDV-Optics without using single mode fibers. So the system can put nearly 1,4 W of Laser power for each wavelength inside the measuring volume, a feat which would be impossible to achieve with mono-mode fibers.