Design and Experimental Test of a Common-path Coherent-dispersion Spectrometer for Exoplanet Searches

Abstract

A coherent-dispersion spectrometer (CODES) system using the radial velocity (RV) method for exoplanet searches is established in this paper. This spectrometer utilizes a new Sagnac interferometer with common-path and asymmetric designs. Compared with the traditional Michelson interferometer-based spectrometer for exoplanet detection, these designs markedly improve the stability of the optical path difference (OPD) to positional changes in optical elements or air density changes, reducing the need for active cavity stabilization. Furthermore, the asymmetric Sagnac design allows convenient separation of the two complementary outputs. In order to verify the feasibility of the CODES, an optical Doppler shift experiment is constructed in the laboratory. The RV signal was extracted by the phase shifts of the interference fringes produced by the spectrometer. The experimental results show that the obtained retrieved RV is 76.7 m s −1 , with an absolute error of 0.3 m s −1 compared to simulated values. And the root mean square error (RMSE) and the standard deviation (STD) are 21.3 m s −1 and 21.4 m s −1 , respectively. Error analyses show that the OPD change caused by the temperature variation is the main factor for the RMSE and STD.

Method for boosting dispersive spectrograph stability 1000× using interferometry with crossfaded pairs of delays

“…Not to, say, 0.03/15000 ∼2 × 10 −6 of a fringe, which is the 3-cm∕s desired precision level of the Doppler measurement for a 1.1-cm delay at 0.54 μm wavelength (velocity per fringe proportionality of cλ∕τ ∼ 15 km∕s per fringe). (Even if the delay is naturally very stable, such as with a Sagnac design, 24 we recommend using an absolute spectral reference. )…”

“…Other groups have worked on improving the interferometer design. Wei et al 24 constructed an EDI using a Sagnac style interferometer rather than Michelson design. Because the Sagnac uses counter propagating beams sharing the beam path, it can have a more stable delay value, which has practical benefits.…”

Research on the Effect of Vibrational Micro-Displacement of an Astronomical Camera on Detector Imaging

“…In the field of astronomy, since the target light all comes from stars outside of Earth, and in some cases, far outside the Milky Way, it usually takes a long integration time to capture the weak light signals, and vibrations cause micro-displacements in the camera itself [5]. If there is relative motion between the camera and the subject during the exposure process, image shift mismatch or imaging blurring can occur, reducing detection accuracy [6].…”