# Can laser interferometer be used on light scattering angled objects?

I want to know if it is possible to use laser interferometer on object with rough texture that is not like mirror, kind of like matte paint that scatters incoming light and on object whose geometry is such that the surface will be angled and curved at the point where the laser beam will aim, it will not be flat directly facing the laser.Also it will move not just perfectly straight in the direction of beam, it will move little bit side to side or up and down on top of closer/further movement.

For example, imagine moving a finger up and down and then measuring it from angle so the finger moves up and down but also gets closer and further, is it possible to detect change in distance from the laser to the point on the finger where the beam is aimed at in that moment?

The simple answer is "yes, interferometry can be used to detect motion of diffusely reflective objects". If velocity is the thing you want to detect, reflected light can be interfered with reference light to obtain a beat frequency that relates directly to velocity. If change in position is what you want to detect, reflected light can be interfered with reference light and phase of the beat frequency can be tracked to get a direct measurement of displacement. The instruments are expensive and a bit complicated, but can be made. If absolute position is what you want to detect, interferometry can also be used: a pulse of "chirp" (sweeping from high to low or low to high frequency) modulated light, reflected off the object, is compared with a reference to determine precisely how long the light took to go from a source to the object and back.

Edit 12/20/18: The third example, using a "chirped" pulse, isn't interferometry in the literal sense, but is mathematically equivalent. Most people - even practitioners of interferometry - think of nearly stationary interference fringes when they use the word "interferometry". That is what could be called "spatial interferometry". An optical beat frequency amounts to interference fringes moving rapidly, and could be called "temporal interferometry".

Yes but not with an interferometer. But unless you need to measure to a few nm you don't need an interferometer.

You can use either a laser distance meter "Disto" long range and accurate to a few mm but with a low update rate.

Or a laser triangulation sensor extremely accurate over a short distance and capable of very high speed, but only work for a small range of target positions.

• You say no but S. McGrew says yes. Please explain why it cant be used in way as I described. – wav scientist Dec 21 '18 at 4:32
• Please see the edit to my answer. – S. McGrew Dec 21 '18 at 5:05
• The disto devices use phase of a varying intensity laser signal - as the posters says the math is the same as interferometry but you aren't interfering the individual photons as in eg a Michelson interferometer – Martin Beckett Dec 21 '18 at 6:12