A laser doppler vibrometer is like a special tool that helps people see how things are moving. It uses a laser beam, which is like a really strong flashlight that shoots out a thin line of light. The laser beam is pointed at an object, like a toy car, and then the vibrations of the toy car make the light of the laser beam change a little bit. The laser doppler vibrometer can see these changes and use them to figure out how fast the toy car is moving or how it is shaking.
Just like how music makes your body vibrate when you feel the bass, everyday things like machines and engines vibrate too. By using a laser doppler vibrometer, people can see how fast and how much things are vibrating. It is very helpful for things like testing airplane engines or making sure machines are working properly.