Fiber-optic vibrometers simplify vibration measurement where physical access is difficult, close stand-off-distances are required, and when relative motions between two points need to be measured. The sensor heads utilize flexible fiber-optics and an output lens to deliver the laser probe to the measurement point and to collect the reflected light as an input to the interferometer. This design allows for fiber-optic cables with diameters as small as 5 mm and lenses that focus the laser down to a 3 µm diameter spot. A special, dual-fiber design (OFV-552) permits the direct measurement of differential movements between two monitored points. The flexibility and small size of the fiber delivery enables measurements in hard-to-reach and space-limited areas.