Editing Particle image velocimetry (section)

===Laser and optics===
For macro PIV setups, [[lasers]] are predominant due to their ability to produce high-power light beams with short pulse durations.  This yields short [[shutter speed|exposure times]] for each frame. [[Nd:YAG laser]]s, commonly used in PIV setups, emit primarily at 1064&nbsp;nm wavelength and its [[harmonics]] (532, 266, etc.)  For safety reasons, the laser emission is typically [[Band-pass filter|bandpass filtered]] to isolate the 532&nbsp;nm harmonics (this is green light, the only harmonic able to be seen by the naked eye).  A [[fiber-optic cable]] or liquid light guide might be used to direct the laser light to the experimental setup.

The optics consist of a [[spherical lens]] and [[cylindrical lens]] combination.  The cylindrical lens expands the laser into a plane while the spherical lens compresses the plane into a thin sheet.  This is critical as the PIV technique cannot generally measure motion normal to the laser sheet and so ideally this is eliminated by maintaining an entirely 2-dimensional laser sheet. The spherical lens cannot compress the laser sheet into an actual 2-dimensional plane.  The minimum thickness is on the order of the [[wavelength]] of the laser light and occurs at a finite distance from the optics setup (the focal point of the spherical lens).  This is the ideal location to place the analysis area of the experiment.

The correct lens for the camera should also be selected to properly focus on and visualize the particles within the investigation area.