Coherence length controller
AssigneeThe Boeing Company
InventorsSteven Edward Muenter, Todd Harding Tomkinson
Life of this patent
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Abstract
Techniques for producing higher fidelity interferometer measurements by reducing sensitivity to spurious sources include reducing the coherence length of an electromagnetic beam. In addition, multiple surfaces within an optical system may be measured by electronically tuning the position of a coherence plane along the optical paths of an interferometer. A phase modulator is used in conjunction with a long coherence length electromagnetic source to generate beams for each leg of an interferometer. Providing a controlled broadband RF signal to the phase modulator increases the bandwidth of the beam and thereby reduces the coherence length of the beam. This reduces the spurious contributions to the output interference fringes from undesired surfaces along the beam path.
Claims18
A method for controlling a coherence length of a coherent radiation beam within an interferometer system, comprising:
- providing a coherent radiation source to generate the coherent radiation beam;
- splitting a reference beam from the coherent radiation beam;
- splitting a measurement beam from the coherent radiation beam;
- applying the measurement beam to a sample;
- generating an output pattern in response to an interference between the reference beam and the measurement beam;
- applying a phase modulator to one of the reference beam and the measurement beam;
- providing a broadband radio frequency (RF) signal to the phase modulator in response to a pseudorandom noise signal;
- and
- controlling the broadband RF signal to improve a contrast of the output pattern.
A method for controlling a coherence length of a coherent radiation beam within an interferometer system, comprising:
- providing a coherent radiation source to generate the coherent radiation beam;
- splitting a reference beam from the coherent radiation beam;
- splitting a measurement beam from the coherent radiation beam;
- applying the measurement beam to a sample;
- generating an output pattern in response to an interference between the reference beam and the measurement beam;
- applying a phase modulator to one of the reference beam and the measurement beam;
- providing a broadband RF signal to the phase modulator, comprising
- providing a pseudorandom noise signal,
- providing an RF carrier signal, and
- mixing the pseudorandom noise signal with the RF carrier signal to generate the broadband RF signal;
- and
- controlling the broadband RF signal to improve a contrast of the output pattern.
A method for controlling a coherence length of a coherent radiation beam within an interferometer system, comprising the steps of:
- providing a coherent radiation source to generate the coherent radiation beam;
- splitting a reference beam from the coherent radiation beam;
- splitting a measurement beam from the coherent radiation beam;
- applying the measurement beam to a sample;
- generating an output pattern in response to an interference between the reference beam and the measurement beam;
- applying a phase modulator to one of the reference beam and the measurement beam;
- providing a broadband RF signal to the phase modulator;
- and
- controlling the broadband RF signal to improve a contrast of the output pattern by controlling a bandwidth of a pseudorandom noise signal.
Dependencies are inferred from the claim text.