Optimization of atomic Faraday filters in the presence of homogeneous line broadening

Abstract

We show that homogeneous line broadening drastically affects the performance of atomic Faraday filters. We study the effects of cell length and find that the behaviour of ‘line-centre’ filters are quite different from ‘wing-type’ filters, where the effect of self-broadening is found to be particularly important. We use a computer optimization algorithm to find the best magnetic field and temperature for Faraday filters with a range of cell lengths, and experimentally realize one particular example using a micro-fabricated 87Rb vapour cell. We find excellent agreement between our theoretical model and experimental data.

Optimized ultra-narrow atomic bandpass filters via magneto-optic rotation in an unconstrained geometry

“…and K, we find a "wing-type" filter [11,15]. Of all the results, the Cs D2 line filter has the highest FOM value of 1.24 GHz −1 .…”

“…2, we show examples of optimized profiles for the D2 lines of Na, K, Rb (naturally abundant), and Cs. For Rb and Cs, we find an optimum filter operating in the "line-center" mode [11,15] whereas, for Na Fig. 1.…”

“…Using this FOM, we can maintain reasonably large transmission while minimizing ENBW. This FOM has previously been used to find the optimal performance of atomic Faraday filters [14,15] and, in the case of an unconstrained magnetic field angle, to theoretically predict improved performance on the Cs D2 line [38]. Figure 1 shows a schematic of the optical setup and the geometry of the situation.…”

“…Computer optimization in the Faraday geometry has been previously demonstrated [14,15,41,44] but, in the unconstrained geometry, the problem is more computationally difficult. In addition to some fixed parameters (element and relative isotopic abundance, cell length, and D line), there are four parameters that the optimization routine can vary.…”

“…We find that by relaxing the constraint of the magnetic field angle, with respect to the light propagation axis, the performance as measured by a FOM can be greatly increased over Table 1. Zero of the detuning axis is the weighted line-center of the respective D2 lines [15,46]. Note that the K and Rb filters are naturally abundant isotopic mixtures.…”