Echelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal

Area of Science:

• Astronomy
• Optical Physics
• Laser Technology

Background:

• Astronomical spectrographs require precise wavelength calibration for accurate data.
• Frequency combs offer a highly stable and precise light source for calibration.
• Existing methods may have limitations in terms of spectral range or complexity.

Purpose of the Study:

• To outline the construction of an astronomical frequency comb.
• To serve as a wavelength reference for échelle spectrographs.
• To achieve high accuracy and stability in the frequency comb.

Main Methods:

• Utilizing a harmonically mode-locked fiber laser (1.56 microm central wavelength) as the source.
• Achieving a repetition rate >7 GHz and peak optical power ~8 kW.
• Employing a two-step nonlinear conversion process (periodically poled lithium niobate and photonic crystal fiber) for visible light generation.
• Linking mode spacing and comb tooth to separate frequency references for accuracy, avoiding a Fabry-Perot cavity.

Main Results:

• The design details a method for generating an astronomical frequency comb.
• The proposed method achieves a high repetition rate and optical power.
• The frequency comb can be made accurate by external frequency references, even without an octave-spanning spectrum.

Conclusions:

• The described frequency comb construction provides a viable wavelength reference for échelle spectrographs.
• Experimental testing is required to validate supermode suppression and sideband asymmetry.
• This approach offers a pathway to enhance the precision of astronomical observations.