Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb

Area of Science:

• Spectroscopy
• Optical Physics
• Molecular Spectroscopy

Background:

• Accurate determination of the complex refractive index is crucial for understanding molecular properties.
• Existing spectroscopic methods often require calibration or are limited in the spectral range they can cover.

Purpose of the Study:

• To introduce and demonstrate a novel calibration-free spectroscopic technique for measuring the complex refractive index of molecular bands.
• To showcase the simultaneous measurement of absorption and dispersion spectra over a broad spectral range.

Main Methods:

• Broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS) utilizing a Fabry-Perot cavity.
• Measurement of cavity transmission spectra using an optical frequency comb and a mechanical Fourier transform spectrometer.
• Analysis of cavity mode broadening and shift to retrieve absorption and dispersion spectra.

Main Results:

• Simultaneous measurement of absorption and dispersion spectra for three CO2 combination bands.
• Successful operation in the 1525 nm to 1620 nm range.
• Good agreement between experimental results and theoretical models.

Conclusions:

• CE-CRIS provides a calibration-free method for determining the complex refractive index of molecular bands.
• The technique enables simultaneous measurement of multiple spectral bands, enhancing precision spectroscopy.
• This method has potential applications in various fields requiring accurate molecular characterization.