Foreign object debris discrimination with modulated laser light
A method of foreign object debris discrimination includes illuminating a particle located within a sensing volume with a modulated electromagnetic radiation pulse emitted from a source; receiving one or more electromagnetic radiation return signals that have been scattered by the particle illuminated by the modulated electromagnetic radiation pulse at a detector; mixing, using a controller, the electromagnetic radiation return signal of amplitude I RS and frequency f RS with a reference signal of amplitude I LS and frequency f RS ; analyzing, using the controller, an amplitude of the mixed signal √{square root over (I LS I RS )}, and frequency of the mixed signal, f RS −f LS ; and classifying, using the controller, a particle position, a velocity, and electromagnetic characteristic of the particle based on the amplitude, √{square root over (I LS I RS )}, and frequency, f RS −f LS of the mixed signal.
1. A method of foreign object debris discrimination, comprising:
illuminating a particle located within a sensing volume with a modulated electromagnetic radiation pulse emitted from a source;
receiving one or more electromagnetic radiation return signals that have been scattered by the particle illuminated by the modulated electromagnetic radiation pulse at a detector;
mixing, using a controller, the electromagnetic radiation return signal of an amplitude and a frequency with a reference signal of an amplitude and a frequency;
analyzing, using the controller, an amplitude of the mixed signal and frequency of the mixed signal;
determining a velocity of the particle and a relative distance with respect to the source with a triangular modulation depending on a modulation rate B/T measuring two beats (Δf up and Δf down ) where the source emits at a frequency within a modulation bandwidth (B=f max −f 0 ) and
classifying, using the controller, a particle position, velocity, and an electromagnetic characteristic of the particle based on the amplitude and frequency of the mixed signal.
2. The method as recited in claim 1 , wherein the reference signal with the amplitude I LS and the frequency f LS is amplified by the return signal with the amplitude I RS and the frequency f RS .
3. The method as recited in claim 2 , wherein analyzing, using the controller, the amplitude of the mixed signal (√{square root over (I LS I RS )}) further comprises scattering information from the particle, its scattering regime
(
a
λ
)
provides particle characteristic size, a, information.
4. The method as recited in claim 1 , wherein analyzing, using the controller, the amplitude of the mixed signal comprises signals from different viewing angles.
5. The method as recited in claim 1 , wherein analyzing, using the controller, the amplitude of the mixed signal comprises signals from different wavelengths.
6. The method as recited in claim 1 , wherein the electromagnetic characteristic further comprises the particle's complex index of refraction.
7. The method as recited in claim 1 , wherein the modulated electromagnetic radiation pulse emitted from the source is used as both to transmit a signal to illuminate particles and as a reference to provide a local modulated signal.
8. The method as recited in claim 1 , wherein the modulated electromagnetic radiation pulse emitted from the source is emitted as a single frequency.
9. The method as recited in claim 1 , further comprising determining a velocity of the particle using the particle's Doppler shift from the frequency of the mixed signal (f RS −f LS ).
10. The method as recited in claim 1 , wherein the particle velocity is determined with a relative position of the particle.