Lamb-Dicke sub-recoil narrowing of high-power CW stokes Raman source
Matthieu Chafer, Anton Husakou, Benoît Debord +2 more
Summary form only given. A new way to reach the Lamb-Dicke regime in molecular gases has been reported in [1]. This is achieved by trapping H2molecule during Stimulated Raman Scattering (SRS) in a photonic band gap hollow-core fiber (PBG HC-PCF) pumped with a high power CW laser [1]. The molecular trapping process occurs in a self-assembled manner, whereby the Raman active molecules are confined in nanometer-wide sections by a periodic and ultra-deep potential thanks to a spatially modulated Raman saturation. It has permitted to obtain sub-recoil linewidths as low as 14 kHz which is 5 orders of magnitude lower than the expected H2Doppler-broadened linewidth for a product of the input power and the pressure below 1000 W.bar. Above this threshold the linewidth broadens due to the generation of the second-order Stokes.Here, we report a further linewidth narrowing down to 2.7 kHz by increasing the length and decreasing the gas pressure. Longer fiber lowers the pump power required for the SRS generation and enables formation of the trapping potential for lower gas pressure, which in turn reduces the molecular collision rate. The Stokes generation was obtained using a set-up similar to the one used in [1]. The PBG fiber has been tailored in order to have a spectral window between 1000 and 1200 nm in order to filter out any other Raman generation except the first rotational Stokes S00(1) at 1131.4 nm. The range of pressure of H2 with which we filled the PBG fiber is from 5 to 50 bars. The pump laser is a narrow linewidth (400 kHz) CW laser with a maximum pump power Pin of 100 W. Figure 1(a) shows the typical linewidth trace of the forward emitted Stokes for a fiber length of 30 m, a gas pressure of 20 bar and a pump power of 12 W. Figure 1(b) shows a resolved spectrum of the Stokes central line, which demonstrates a linewidth of 2.7 kHz. This line is nearly 30 times narrower than the hydrogen molecule recoil frequency Vrecο1 = πh(mλs2) of ~78 kHz, 5 orders of magnitude narrower than the Doppler width and almost 6 orders of magnitude narrower than the H2 pressure broadened line. Linewidth(kHz)
Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2017•0 citations