A simulation of MOF transmission profiles: lights and shadows

Magneto-optical filters (MOF) are widely used in astronomy as well as in other fields of research because of their characteristics, which includes: narrow passband (~ 50 mÅ at transmission peaks), high transmission (max. 50% for incoming unpolarized light), high out-of-band rejection (10^5), large field of view which makes them suitable for imaging, absolute wavelength reference and, hence, spectral stability. Therefore, it would be worthwhile to implement a theoretical simulation of the filter which enables to make reliable predictions of the filter transmission as a function of the two main parameters controlling the filter performances, i.e. the temperature at which the cell is heated and the external magnetic field in which the cell is embedded. On the track of the pioneering work of Cacciani et al. (1994), we present a numerical simulation of a potassium MOF which can compute the filter transmission, taking into account: spatial variations of temperature and magnetic field inside the cell, broadening induced by the buffer gas, and hyperfine structure of the K I D1 resonance line, including isotopic shifts between the K 39 and K 41 isotopes. The results of the simulation are compared with experimental transmission profiles at different heating temperatures, measured with a diode laser system. The comparison reveals a significant amount of agreement but also shows some important differences which deserve further work to be fully explained.