Hollow cathode lamp based Faraday anomalous dispersion optical filter

Abstract

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. 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. To avoid this restriction, we propose a scheme of FADOF based on the hollow cathode lamp (HCL), instead of atomic vapor cells. Experimental results in strontium atoms verified this scheme, where a transmission peak corresponding to the 88Sr (5s2)1S0 − (5s5p)1P1 transition (461 nm) is obtained, with a maximum transmittance of 62.5% and a bandwith of 1.19 GHz. The dependence of transmission on magnetic field and HCL discharge current is also studied. 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.

A Faraday laser operating on Cs 852 nm transition

“…The successful development of the 852 nm Faraday laser predicts potential possibility for the implementation of Faraday laser based on similar high-transmission Faraday optical filter. Therefore, this method can greatly expand the application of alternate operating wavelengths for the other alkali-metal atoms, including high melting point metals [38].…”

“…Since Faraday anomalous dispersion optical filter was introduced in 1956 [30], Faraday optical filters composed of different elements have been developed [31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Faraday optical filters have been used as frequency-selecting element and applied to various applications, including Na guide-star [45], Mollow triplet filtering [46], Faraday geometry [47], Doppler lidar [48] and active optical clock [49].…”

Excited-state population distributions of alkaline-earth metal in a hollow cathode lamp

“…Hence, the samples of atomic filters have to be heated to high temperatures to get an atomic density high enough to guarantee the transmittance [9,10] . To overcome this limitation, an innovative method of utilizing an HCL to realize a Sr element FADOF was proposed, as the HCLs can provide the high atomic density at room temperature [11] . Moreover, since the state-of-the-art HCLs cover about 70 kinds of high melting point metal elements, we believe that, due to its rich spectral lines, without heating, scalability, low fabrication cost, and potential applications in various atomic spectra [12][13][14][15][16] they can be used in submarine communication systems as well as excited-state FADOFs without the use of a pump laser [5,6] .…”

Faraday laser at Rb 1529 nm transition for optical communication systems

“…Since Faraday anomalous dispersion optical filter (FADOF) technology was introduced in 1956 [18] , different kinds of applications of FADOF have been carried out for its advantages of high transmission, ultra-narrow bandwidth, and high noise rejection [18][19][20][21][22][23] , such as laser communications [24] , remote sensing [25] , lidar systems [26] , and Faraday laser [27][28][29][30] . So far, FADOFs operating on a variety of wavelengths in the ultraviolet, visible, and near-infrared have been reported [31][32][33] . Although both the original Rb LESFADOF operating on the Rb 5P 3∕2 − 4D 5∕2 transition (1529.4 nm in a vacuum) without an additional frequencystabilized pump laser [17] and the Faraday laser lasing on 780 nm ground-state transition have been previously reported [27] , unfortunately, the excited-state Faraday laser has never been realized due to the low transmittance of the LESFADOF.…”

“…Similar high-transmission Faraday filters can be engineered for alternate operating wavelengths for the other alkaline-earth metal atoms [30] , so, in principle, this type of design is generally applicable to all alkaline-earth elements. Moreover, the successful development of the LESFADOF-based Faraday laser predicts potential possibilities for the implementation of a Faraday laser based on a hollow-cathode-lamp-based FADOF [32] . Therefore, this scheme can greatly expand the application of other wavelengths corresponding to atomic transitions of about 70 kinds of elements, including high melting point metals [32] .…”