Refractivity corrected distance measurement using the intermode beats derived from a supercontinuum.

Area of Science:

• Optical metrology
• Interferometry
• Supercontinuum generation

Background:

• Accurate distance measurements are crucial in various scientific and industrial applications.
• Atmospheric conditions, specifically variations in the refractive index, introduce significant errors in optical distance measurements.
• Traditional methods often require external sensors or complex environmental monitoring to compensate for refractive index changes.

Purpose of the Study:

• To demonstrate a supercontinuum-based approach for highly accurate distance measurements.
• To implement inline refractivity compensation using simultaneous measurements at two optical wavelengths.
• To achieve precise distance estimations by mitigating deviations caused by unknown refractive indices.

Main Methods:

• Utilized a supercontinuum (SC) source, coherently broadened from a 780 nm frequency comb, spanning 570-970 nm.
• Performed distance measurements by analyzing phase delay observations on intermode beats at 590 nm and 890 nm.
• Introduced controlled refractivity variations using pressure changes over a 15 m path to test compensation.

Main Results:

• Achieved distance measurements with standard deviations of approximately 0.01 mm at 50 m.
• Observed distance-dependent components below 0.2 ppm on individual spectral bands.
• Demonstrated refractivity-corrected distance measurements with a standard deviation of ~0.08 mm over 60 s averaging, despite induced optical path length changes of 0.4 mm.

Conclusions:

• The supercontinuum-based two-color method effectively compensates for inline refractivity variations.
• The system offers high accuracy (0.1 ppm residuals over 50 m) and is extensible to multi-wavelength measurements.
• This approach holds significant potential for practical, long-distance metrology applications requiring precise environmental compensation.