![]() ![]() Therefore it is imperative to introduce an external mechanism that provides energy to the system and break the thermal equilibium. In order to get free from the heating problem and extend elements variety of FADOF, it is necessary to achieve high density vapor at lower temperature. So far, only FADOFs of calcium have been reported with complex experimental devices, such as an atomic beam 26 and a stainless steel cell of which the sapphire viewports mounted on the ends 27. ![]() In conventional method, the atomic density is determined by thermal equilibium, therefore the samples of atomic filters have to be heated to high temperatures to get an atomic density high enough to guarantee the transmittance 24, 25. For elements with high melting-points, such as alkaline earth metals, it is much difficult to realize FADOFs due to the toughness of preparing atomic vapor with high density. Low melting-point metals are usually used in most FADOF designs, such as mercury (254 nm) 16, potassium (766 nm) 17, sodium (589 nm) 18, rubidium (780 nm 19 and 795 nm 20), cesium (459 nm 21 and 894 nm 22) and the ESFADOF of rubidium (776 nm 23), etc. Besides, with the characteristics of ultranarrow bandwidth 7, high transmission and high noise rejection 8, 9, the FADOFs can also be used as frequency selective components in free-space optical communication 10 and lidar remote sensing systems 11, 12, 13, 14, 15. Moveover, the FADOF has been directly built into an active optical clock 6. In recent years, it has been demonstrated that the FADOF can be used in all-optical frequency locking 3 and the building of diode lasers immune to current and temperature fluctuations 4, 5. The application of FADOFs in laser stabilization was first realized in 1969 2. In particular, the advantages of ultra-narrow bandwidth and high accuracy makes it an excellent candidate for laser stabilization. Since the state-of-art commercial HCLs cover about 70 elements, this scheme can greatly expand the applications of FADOFs and the abundant atomic transitions they provide bring the HCL based FADOFs potential applications for frequency stabilization.įaraday anomalous dispersion optical filter (FADOF) 1 has been widely investigated in laser stabilization and optical communication systems because of their frequency selectivity and ease of fabrication. The dependence of transmission on magnetic field and HCL discharge current is also studied. Experimental results in strontium atoms verified this scheme, where a transmission peak corresponding to the 88Sr (5 s 2) 1 S 0 − (5 s5 p) 1 P 1 transition (461 nm) is obtained, with a maximum transmittance of 62.5% and a bandwith of 1.19 GHz. To avoid this restriction, we propose a scheme of FADOF based on the hollow cathode lamp (HCL), instead of atomic vapor cells. In conventional FADOF systems a high atomic density is usually achieved by thermal equilibrium at the saturated vapor pressure, hence for elements with high melting-points a high temperature is required. The Faraday anomalous dispersion optical filter (FADOF), which has acquired wide applications, is mainly limited to some gaseous elements and low melting-point metals before, for the restriction of the attainable atomic density. ![]()
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