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Active cancellation of residual amplitude modulation in a frequency-modulation based Fabry-Perot interferometer
Yinan Yu1, Yicheng Wang1, Jon R Pratt1
1National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
The Review of Scientific Instruments
|April 3, 2016
Summary
Residual amplitude modulation (RAM) is a key noise source in spectroscopy. We developed a simple method to cancel RAM, improving laser frequency stability measurements and reducing temperature-dependent errors in capacitance measurements.
Area of Science:
- Optical metrology
- Spectroscopy
- Precision measurement
Background:
- Residual amplitude modulation (RAM) significantly degrades sensitivity in frequency modulation spectroscopy.
- Temperature-dependent birefringence in modulator crystals causes RAM by shifting optical axis orientation.
- RAM in fiber-based interferometers affects laser frequency stability and correlates with temperature.
Purpose of the Study:
- To demonstrate a method for canceling excessive RAM caused by polarization mismatch.
- To improve the accuracy of laser frequency noise measurements.
- To mitigate temperature dependencies in cavity length and capacitance measurements.
Main Methods:
- Developed a technique to cancel RAM by addressing polarization mismatch.
- Measured frequency noise of a heterodyne beat between two lasers.
- Locked lasers to different resonant modes of an optical cavity.
Main Results:
- Achieved measurement accuracy better than 0.5 ppm for laser frequency noise.
- Successfully mitigated temperature dependency in cavity length measurements.
- Reduced temperature-induced errors in capacitance measurements.
Conclusions:
- The demonstrated RAM cancellation approach enhances precision in optical measurements.
- This method is crucial for accurate determination of longitudinal mode numbers in optical cavities.
- The technique significantly improves the stability and reliability of precision metrology systems.
