Final answer:
Laser rangefinders face range ambiguity due to the coherent nature of laser light, where multiple locations along the laser's path differing by integer multiples of the wavelength lead to the same phase difference at the detector, causing constructive interference and an inability to distinguish actual distances.
Step-by-step explanation:
Amplitude-modulated (or intensity-modulated) laser rangefinders are subject to range ambiguity due to the nature of electromagnetic wave propagation and detection. To understand this, we can look at the properties that make lasers highly suitable for varied applications. Lasers produce single-wavelength electromagnetic (EM) radiation, and this radiation is very coherent, meaning the emitted photons are in phase with each other. The precision in manipulating coherent light allows for accurate applications, such as range-finding. However, the same properties introduce limitations.
In a laser rangefinder, the phase difference at each point is a result of different path lengths traveled by the wave. If the difference in the path lengths is an integer multiple of the wavelength, we encounter a situation of constructive interference, indicated by maximum intensity at point P. This phenomenon may lead to uncertainty in measuring distances as the instrument can't distinguish between multiple locations that have a path length difference of an integer multiple of the wavelength. Essentially, the range may appear the same for a target at an actual distance or any multiple of the modulation wavelength away from it, this is the range ambiguity.
The concept akin to this is reflected by Heisenberg's uncertainty principle in quantum mechanics, where there are fundamental limits in precision when dealing with observables like position and momentum. Similarly, in laser rangefinding, the fundamental limitation is based on the wavelength of the probe, which in case of modulation, refers to the wavelength of the laser light used.