Atomic Faraday filter with equivalent noise bandwidth less than 1  GHz

Abstract

We demonstrate an atomic bandpass optical filter with an equivalent noise bandwidth less than 1 GHz using the D1 line in a cesium vapor. We use the ElecSus computer program to find optimal experimental parameters, and find that for important quantities the cesium D1 line clearly outperforms other alkali metals on either D-lines. The filter simultaneously achieves a peak transmission of 77%, a passband of 310 MHz and an equivalent noise bandwidth of 0.96 GHz, for a magnetic field of 45.3 gauss and a temperature of 68.0• C. Experimentally, the prediction from the model is verified. The experiment and theoretical predictions show excellent agreement.The Faraday effect in atomic media has come to be used for a wide range of applications, including creating macroscopic entanglement [1], GHz bandwidth measurements [2], non-destructive imaging [3], magnetometry [4], off-resonance laser frequency stabilization [5,6], and creating an optical isolator [7].Another application of increasing interest is utilizing the Faraday effect to create ultra-narrow bandwidth optical filters [8], of the order of a GHz width. These atomic Faraday filters are imaging filters [9] with a large field of view [10], and can be engineered to be low loss at the signal frequency [11]. This makes them the filter of choice for many applications, for example, they are used in atmospheric lidar [11][12][13][14] [9,24,25,[31][32][33][34], potassium [18,35,36], rubidium [37][38][39], and cesium [23,40,41]. A Faraday filter on the cesium D 1 line (894 nm) could be useful for quantum optics experiments which utilize the the Cs D 1 line [42], and could aid filtering degenerate photon-pairs at 894 nm in a similar way to that shown for 795 nm [21].In this letter we demonstrate the technique of using computer optimization to find optimal working parameters for a Faraday filter. Using this technique we find that a Faraday filter working at the Cs D 1 line has superior performance when compared to similar linear Faraday filters working with different elements and/or transitions. Experimentally, we verify the prediction of the model, and achieve a linear Faraday filter with the best performance to date.

Tunable and polarization-controlled high-contrast bright and dark coherent resonances in potassium

“…We have obtained EIA resonances with amplitude comparable with Our results thus disclose new paths for EIA applications, from state manipulation in fundamental physics and metrology, to tunable and narrowband optical and photonic devices. Examples include: atomic optical isolators [33,34], atom-based polarization filters and splitters, atomic filters with sub-MHz band [35][36][37], and cavity-less bistable systems and switches [38,39], all with potential for reduced dissipation, fast switching time and efficiency tunability, not to mention control of light group velocity [9] and novel photonic metamaterials [10]. …”

An atomic spectrum recorded with a single-molecule light source

“…This is calculated by the integrated transmission, T, for all relevant wavelengths, divided by the peak transmission at the point of maximal transmission (ν S ), as ENBW = T (ν)dν T (ν S ) . It describes the peak to background ratio and amounts to below 5 GHz in the case for the filter on the sodium D 2 -line [42][43][44].…”

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

“…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.…”

“…The choice of vapor cell length can drastically affect the optimized performance of the optical filter, as has been previously demonstrated [14]. Experimentally, one needs to balance the optical depth requirements with the ability to produce an approximately uniform magnetic field across the cell.…”