A Dual-Frequency Faraday Laser

Tiantian Shi,Jianxiang Miao,Hong Guo,Duo Pan,Pengyuan Chang,Jingbiao Chen,Bin Luo,Xiaolei Guan

doi:10.1109/jphot.2020.3006503

Abstract

The Faraday laser, with Faraday anomalous dispersion optical filter (FADOF) as frequency-selection element, is a natural narrow-bandwidth light source for laser physic experiments. In this work, a dual-frequency (DF) Faraday laser is demonstrated for the first time on Cs D2 line at 852 nm. The frequencies of the two modes of DF Faraday laser hinge on the peak transition frequencies of 852 nm FADOF transmittance spectrum corresponding to the ground state F=4 and F=3. The frequency difference between the two modes is tunable over a range of 1.4 GHz with the temperature of Cs vapor cell inside the FADOF. The linewidth of each laser mode is less than 33 kHz. Furthermore, the most probable linewidth of the beat-note spectra between the two modes is 902.95 Hz at different vapor-cell temperatures. Such a DF Faraday laser has many potential applications in atomic physics, such as sub-Doppler spectroscopy and coherent population trapping atomic clocks.

Highlights

Faraday anomalous dispersion optical filter (FADOF) [1], [2], with superiorities of high noise rejection, narrow bandwidth [3], [4], and high transmission, has been detailedly studied in theory and experiment based on different atomic species, such as Na [5], Rb [6], K [7], [8] and Cs [9], [10], for over 60 years [11]
The light output from 852 nm interference filters (IFs)-external-cavity diode lasers (ECDLs) is divided into two parts, where one part is stabilized by saturation absorption spectroscopy (SAS) to provide a frequency reference, and the other, which is different from the scheme in Fig. 1, enters the FADOF in the external cavity of the DF Faraday laser
The bottom is the FADOF transmittance spectrum on Cs D2 line consists of two passbands, which corresponds to 62S1/2(F = 4) → 62P3/2 and 62S1/2(F = 3) → 62P3/2 hyperfine lines, respectively, with vapor-cell temperature T = 43 ◦C and axial magnetic filed B = 330 G

Summary

Introduction

Faraday anomalous dispersion optical filter (FADOF) [1], [2], with superiorities of high noise rejection, narrow bandwidth [3], [4], and high transmission, has been detailedly studied in theory and experiment based on different atomic species, such as Na [5], Rb [6], K [7], [8] and Cs [9], [10], for over 60 years [11]. Utilizing the anomalous Faraday effect [9], only the signal with frequency near atomic resonance can be transmitted. The FADOF is an excellent filter to distinguish the useful signal from background noise, which is widely applied in optical communication [9], atmospheric lidar [12], [13], and frequency stabilization of diode laser [14]–[16]. Compared with the typical external-cavity diode lasers (ECDLs) utilizing interference filters (IFs) [21], [22], gratings [23], [24], or Fabry-Perot etalons [25], [26] as mode-selection elements, the Faraday lasers

Methods

Results

Conclusion