The laser accelerometer is a special type of accelerometer family used when extremely precise measurements are required that cannot be obtained with other types of instruments. The operating principle is based on the physical principle that acceleration is a derivative of velocity over time. In this device, a laser interferometer measures the movement of the moving object instant by instant, and a computer connected to it performs the second derivative with respect to time, thus directly obtaining the acceleration value.
A laser accelerometer consists of a frame with three orthogonal input axes and multiple proof masses, each proof mass having a predetermined blanking surface. A flexible beam supports each proof mass. The flexible beam allows the proof mass to move along the input axis. A laser light source provides a beam of light. The laser source is characterized by a transverse field characteristic having a central zero intensity region. A mirror directs the light beam to a detector. The detector is positioned to be centered on the light beam and is responsive to the transmitted light beam intensity to provide an intensity signal. The intensity signal is characterized to have a magnitude related to the intensity of the transmitted light beam.
The blanking surface of the proof mass is centrally positioned within and normal to the null intensity region of the light beam to provide increased blanking of the light beam in response to transverse movement of the mass on the input axis. The proof mass deflects the flexible beam and moves the blanking surface in a direction transverse to the light beam to partially blank the light beam in response to acceleration in the direction of the input axis. The controller responds to the intensity signal to apply a return force to return the proof mass to a centered position and provides an output signal proportional to the return force.
The problems with these devices are that they are expensive, somewhat bulky, require the interferometer to be mounted on the ground (or in a place that is considered fixed), and the laser must be continuously pointed at the moving object.