Second version of the IZMIRAN solar spectromagnetograph. Part I. Instrument design

The second version of the IZMIRAN solar spectromagnetograph (SM), which is designed for measuring the full vector of the magnetic field and the line-of-sight velocities in the solar photosphere, is described. In contrast to the conventional schemes, the described SM uses the parallel analysis of the spectrum and polarization of optical radiation. The latter could be performed thanks to the method of precise calibration of circuits with multielement photodetectors. The new scheme of the SM allows measurements of the Stokes parameters for two magnetically active lines with an accuracy limited by only the quantum noise of photodetectors.