Velocity interferometer system for any reflector

In recent years another time-resolved velocity measurement tool called laser Doppler velocimetry has achieved popularity in the shock physics community as an adjunct or replacement for VISAR.

As such it requires extremely fast data acquisition devices (digital oscilloscopes with bandwidths of 10 GHz or higher) and is limited in the range of velocities it can cover.

The VISAR on the other hand is configured to 'optically differentiate' so that the light intensity variation due to interference varies sinusoidally with the velocity of the surface not the displacement.

The original VISARs were built at the National Laboratories and had free-space beams on optical tables with discrete optical components such as beam-splitting pellicles, mirrors, quarter wave delay plates, glass etalons, high voltage photo-multiplier tubes, argon ion lasers and so on.

Modern versions such as the Mark IV-3000 from Martin, Froeschner & Associates (mfaoptics.com) implement the same optical arrangement entirely in single-mode optical fibre with all solid state telecomm components such as InGaAs photodiodes, Er doped fibre amplifiers (EDFAs) and extremely high purity (<2 kHz linewidth) lasers.

Profile of a shockwave going through a solid, Adapted from Marc Meyers 's "Dynamic Behavior of Materials"