Dichroic Calibration – A new tool for astronomical frequency calibration

• Applicant: Professor Dr. Ansgar Reiners
• Subject Area: Astrophysics and Astronomy
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575157204

This proposal aims to advance high-precision astronomical spectroscopy by implementing the Dichroic Calibration Concept, a novel strategy recently designed by our team to solve for the current challenges with high-resolution spectrograph wavelength calibration. Traditional calibration methods face limitations due to instability of calibrators and incomplete wavelength coverage. We propose using a Fourier Transform Spectrometer (FTS) to transfer the accurate frequency scale of an absolute reference (such as a Laser Frequency Comb, LFC) onto secondary calibrators, like Fabry-Pérot etalons (FPs), across a broader spectral range. The method opens the new possibility to design optimized calibrators for astronomical applications. The proposed approach has the potential to surpass current calibration limitations and to enable the detection of Earth2.0 or measuring the accelerated expansion of the Universe. The Second Earth Spectrograph (2ES), to be installed at La Silla Observatory, Chile, provides an ideal platform for implementing and testing this concept. The project’s objectives include procuring and integrating a zero-point calibrated FTS including an absolute reference, developing a calibration plan, and achieving routine astronomical operation with simultaneous FTS monitoring. The project serves as a prototype of a new calibration paradigm for existing and future high-resolution spectrographs, such as ANDES for ESO’s Extremely Large Telescope.

• DFG Programme: New Instrumentation for Research
• Major Instrumentation: Fourier Transform Spectrometer ; Stabilized Light Source: LFC
• Instrumentation Group: 1830 Fourier-Transform-IR-Spektrometer ; 5700 Festkörper-Laser
• Participating Institution: Max-Planck-Institut für Astronomie ; Abteilung Planeten- und Sternentstehung