Resonator length measurement
AssigneeAcreo AB and System 3R International AB
InventorsAnders Djupsjobacka, Hakan Dahlquist
Life of this patent
Estimating the term…
Abstract
The invention provides a method and system for measuring the length of a reflective resonator, by analyzing an electromagnetic spectrum emitted therefrom. The emitted spectrum is used for estimating a first cavity length. This estimation is thereafter improved, by first computing at least one interference number for the spectrum, adjust this value to e.g. an integer or half-integer depending on the configuration of the resonator, and thereafter re-calculating the length of the resonator using the adjusted value of the interference number. The above is an efficient way of improving the accuracy in the determination of a physical property of a resonator.
Claims15
A method of determining the distance between a waveguide and the surface of an object, the method comprising:
- providing a resonator having a first and a second reflective end surface, said second reflective end surface being the object surface, the distance to which is to be measured;
- transmitting electromagnetic radiation (λLS) in a waveguide, and emitting said electromagnetic radiation into said resonator, wherein said electromagnetic radiation comprises at least one resonance wavelength;
- forming at least one resonant wave inside said resonator by means of said electromagnetic radiation (λLS);
- transmitting a spectrum of said radiation (SR), emitted out of said resonator, in a waveguide to a recording unit;
- recording said emitted spectrum (SR) by said recording unit, and providing said recorded spectrum to an analyzing unit;
- estimating, at said analyzing unit, at least one value of the resonator length (LEST), wherein said estimating of at least one value of the resonator length (LEST) comprises performing a Fourier transform of at least a portion of said recorded spectrum;
- selecting, at said analyzing unit, at least one mark wavelength (λM) of said spectrum by determining a maximum, a minimum or an inflexion point of said recorded spectrum;
- computing an estimated interference number (IEST), based on a ratio (2*LEST/λM) of two times said at least one value of the resonator length (LEST) and said working wavelength (λM);
- determining an actual interference number (ICORR) as the closest integer or half-integer to said estimated interference number (IEST);
- and
- computing a second value of the resonator length (LCORR) based on half the product (ICORR*λM/2) of said actual interference number (ICORR) and said working wavelength (λM).
A system for determining a distance between a waveguide and the surface of an object, comprising:
- a resonator having a first and a second reflective end surface, said second reflective end surface being the object surface, the distance to which is to be measured;
- a first set of radiation transmitters arranged to transmit electromagnetic radiation (λLS) to said resonator;
- a recorder operative to record an electromagnetic spectrum (SR);
- a second set of radiation transmitters arranged to transmit radiation from said resonator to said recording means;
- and
- analyzer operative to determine a length (L) of said resonator by:
- estimating at least one value of the resonator length (LEST), wherein said estimating of at least one value of the resonator length (LEST) comprises performing a Fourier transform of at least a portion of said recorded spectrum;
- selecting at least one mark wavelength (λM) of said spectrum by estimating a maxima, minima or an inflexion point of said recorded spectrum;
- computing an estimated interference number (IEST), based on a ratio (2*LEST/λM) of two times said at least one value of the resonator length (LEST) and said working wavelength (λM);
- determining an actual interference number (ICORR) as the closest integer or half-integer to said estimated interference number (IEST);
- and
- computing a second value of the resonator length (LCORR) based on half the product (ICORR*λM/2) of said actual interference number (ICORR) and said working wavelength (λM).
Dependencies are inferred from the claim text.