Description
Wavelength calibration establishes a physical scale by mapping absolute wavelengths onto the pixel positions of the detector of any astronomical spectrographs. Precise wavelength calibration is crucial for measuring physical quantities, for example, radial velocities via high-resolution spectrographs. In general, hollow-cathode lamps (e.g. ThAr), Fabry-Perot etalons, and laser frequency combs offer wavelength calibration for high-resolution spectrographs. However, due to their various limitations as calibrators, investigations of any cost-effective alternative methods remain of prime interest. In this presentation, I shall discuss the feasibility of two commercially available solid fused silica etalons with broadband metallic coatings, metalons having different cavity spacing (free spectral range of 1/cm and 0.5/cm) in the laboratory. We studied the behaviour of metalons from theoretical derivation and experimental data and found that theoretical predictions corroborated with experimental measurements. The temperature of the metalon system was controlled with active temperature control methodology using a controlled loop feedback system and an off-the-shelf dewar flask and a temperature stability of 0.8 mK was achieved. We measured radial-velocity drift using standard software, e.g., TERRA and SERVAL and our result demonstrated that metalon is capable of providing higher signal-to-noise calibration and better nightly drift measurement relative to ThAr in the wavelength range between 470 nm and 780 nm. Although a similar result was found earlier from etalons and the metalon solution lacks the efficiency of an etalon, the metalon offers a cost-effective broadband solution free from the ageing of dielectric mirror coatings. Nonetheless, long-term monitoring is required to understand the metalon performance in detail.
