Optimization of filtering schemes for broadband astro-combs

Area of Science:

• Astronomy and Astrophysics
• Optical Engineering
• Laser Physics

Background:

• Astronomical spectrographs require precise wavelength calibration for exoplanet detection.
• Femtosecond laser frequency combs offer potential for high-precision calibration but often have narrow bandwidth and small line spacing.

Purpose of the Study:

• To analyze the design of broadband, large-line-spacing astro-combs for accurate radial-velocity (RV) calibration.
• To investigate the interplay between filter cavities, power amplifiers, and nonlinear fiber in astro-comb systems.
• To optimize astro-comb performance for detecting Earth-like exoplanets.

Main Methods:

• Development of analytic and numeric models to simulate astro-comb performance.
• Evaluation of various Fabry-Perot (FP) filter cavity schemes (identical, co-prime, fraction-prime, conjugate).
• Integration with chirped-pulse amplification (CPA) and highly nonlinear optical fiber for spectral broadening.

Main Results:

• Even minor nonlinear phase can degrade filtered comb line suppression and increase RV error.
• Filtering with two cavities before CPA generally outperforms placing the amplifier between cavities.
• Conjugate cavities achieve <1 cm/s RV calibration error over >300 nm wavelength coverage.

Conclusions:

• The design of astro-combs significantly impacts RV calibration accuracy.
• Conjugate cavity filtering coupled with CPA is a promising approach for high-precision astronomical measurements.
• This technology will advance the search for and characterization of Earth-like exoplanets.