How is pulsed-laser holography used in wind-tunnel experiments?

In wind-tunnel experiments, pulsed-laser holography is used to study high-speed air flow around aerodynamic objects by recording refractive-index changes in the air. These changes are caused by pressure variations as gas deflects around an object.1

This technique serves as an alternative to traditional optical interferometry, which is often difficult to stabilize and requires high-quality, sturdy optical components to minimize distortion under high gas-flow velocities. By using the extremely rapid, high-intensity flash of a pulsed laser—with pulse durations often less than 1/10,000,000 of a second—holography can effectively "freeze" the motion of the air flow. This allows researchers to capture interferometric data without the stringent stability and equipment requirements of classical interferometric systems.1