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)
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)
Trapping or cooling molecules has rallied a long-standing effort for its impact in exploring new frontiers in physics and in finding new phase of matter for quantum technologies. Here we demonstrate a system for light-trapping molecules and stimulated Raman scattering based on optically self-nanostructured molecular hydrogen in hollow-core photonic crystal fibre. A lattice is formed by a periodic and ultra-deep potential caused by a spatially modulated Raman saturation, where Raman-active molecules are strongly localized in a one-dimensional array of nanometre-wide sections. Only these trapped molecules participate in stimulated Raman scattering, generating high-power forward and backward Stokes continuous-wave laser radiation in the Lamb-Dicke regime with sub-Doppler emission spectrum. The spectrum exhibits a central line with a sub-recoil linewidth as low as ∼14 kHz, more than five orders of magnitude narrower than conventional-Raman pressure-broadened linewidth, and sidebands comprising Mollow triplet, motional sidebands and four-wave mixing.
Since the advent of atom laser-cooling, trapping or cooling natural molecules has been a long standing and challenging goal. Here, we demonstrate a method for laser-trapping molecules that is radically novel in its configuration, in its underlined physical dynamics and in its outcomes. It is based on self-optically spatially-nanostructured high pressure molecular hydrogen confined in hollow-core photonic-crystal-fibre. An accelerating molecular-lattice is formed by a periodic potential associated with Raman saturation except for a 1-dimentional array of nanometer wide and strongly-localizing sections. In these sections, molecules with a speed of as large as 1800 m/s are trapped, and stimulated Raman scattering in the Lamb-Dicke regime occurs to generate high power forward and backward-Stokes continuous-wave laser with sideband-resolved sub-Doppler emission spectrum. The spectrum exhibits a central line with a sub-recoil linewidth of as low as 14 kHz, more than 5 orders-of-magnitude narrower than in conventional Raman scattering, and sidebands comprising Mollow triplet, molecular motional-sidebands and four-wave-mixing.
Summary form only given. The development of the Raman gas-filled hollow core photonic crystal fibers allow to exacerbate the light-matter interaction with extremely high efficiency. Among the nonlinear optical effect that were extensively explored we count stimulated Raman scattering, with demonstrations like over 5-octaves wide Raman comb using H2-filled inhibited coupling guiding HC-PCF pumped with a picosecond pulsed laser [1]. Furthermore, Raman-active gases are known to exhibit very weak susceptibility outside the Raman frequencies, and thus are considered to be poor media for the generation of new frequencies through parametric four-wave mixing (FWM).Here we demonstrate, for the first time to our knowledge, the generation of pairs of sidebands via parametric FWM in strongly driven Raman molecular gas. The experimental set-up used a 1030 nm Yb-fiber laser with average power of 15 W, a repetition rate of 1 MHz and pulse duration of 27 ps. The light is then coupled into a photonic microcell composed by a D2-filled inhibited coupling tubular-lattice single-ring HC-PCF [2]. The fiber exhibits a low-loss broadband guidance with a minimum of 10 dB/km around the pump wavelength and operates in almost a single mode regime with a mode field diameter of 28 μm. The D2 molecule has a vibrational Raman resonance around 89.8 THz, and rotational resonances of 12.4 THz for the ortho-D2 and 7.1 THz for the para-D2. The pressure of D2 was set at 40 bar to experimentally maximize the Raman lines from ortho-D2. The results are shown in the figure 1. The generated spectrum presents around 100 laser lines over a 200 THz wide spectral span with a dense cluster whose frequency-difference is under 2 THz by a ro-vib SRS/FWM combination. Four FWM sidebands can be identified (plotted in red color), generated in both sides of two para-rotational lines reproduced eight times around the pump radiation and three times around the first vibrational Stokes.
Backward stimulated Raman scattering in gases provides a promising route to compression and amplification of a Stokes seed-pulse by counter-propagating against a pump-pulse, as has been already demonstrated in various platforms, mainly in free-space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable with, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532-nm-pump. The efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength towards the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.
Backward stimulated Raman scattering in gases provides a promising route to the compression and amplification of a Stokes seed pulse by counter-propagating against a pump pulse, as has been demonstrated already in various platforms, mainly in free space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report, to the best of our knowledge, the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable to, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532 nm pump. Efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers, the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength toward the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.