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Applied Physics Letters

Output-coupling-dependent linewidth narrowing in resonantly pumped diamond Raman lasers

Hui Chen, Wenqiang Fan, Longjie Zhang, Jie Ding, Bingzheng Yan, Yue Wang, Zhiwei Lu, Zi‐Hui Zhang, Zhenxu Bai

Published Oct 26, 2026• 0 citations
Publisher

Abstract

Narrow-linewidth diamond Raman lasers hold significant potential for applications in special-wavelength laser generation, coherent detection, and precision measurement. Resonant pumping is an effective approach for achieving low-threshold excitation of diamond Raman lasers. In this operating regime, the output-coupler transmittance directly affects the Stokes cavity loss, but its influence on the realized Raman linewidth has not been systematically investigated. Here, a narrow-linewidth continuous-wave pump laser combined with Pound–Drever–Hall locking is used to resonantly pump a diamond Raman oscillator, and the Stokes characteristics are compared for different output-coupler transmittances. The output-coupler transmittance significantly affects the Raman lasing threshold, conversion efficiency, locking robustness, and output linewidth. Increasing the transmittance from 0.6% to 3.0% increases the Stokes output power and conversion efficiency but shortens the stable locking duration. Conversely, reducing the transmittance progressively narrows the Stokes linewidth. At a transmittance of about 0.2%, a Stokes linewidth of 5.70 kHz, slightly narrower than that of the pump laser, is achieved. This result indicates that low output-coupling loss extends the intracavity Stokes photon lifetime and enhances the suppression of pump-to-Stokes frequency-noise transfer, thereby enabling linewidth compression. This study reveals the role of output-coupling loss in controlling the linewidth evolution of resonantly pumped diamond Raman lasers and provides important experimental guidance for the design of low-threshold, highly stable, narrow-linewidth diamond Raman lasers.

DOI
10.1063/5.0352290

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Narrow-linewidth diamond Raman lasers hold significant potential for applications in special-wavelength laser generation, coherent detection, and precision measurement. Resonant pumping is an effective approach for achieving low-threshold excitation of diamond Raman lasers. In this operating regime, the output-coupler transmittance directly affects the Stokes cavity loss, but its influence on the realized Raman linewidth has not been systematically investigated. Here, a narrow-linewidth continuous-wave pump laser combined with Pound–Drever–Hall locking is used to resonantly pump a diamond Raman oscillator, and the Stokes characteristics are compared for different output-coupler transmittances. The output-coupler transmittance significantly affects the Raman lasing threshold, conversion efficiency, locking robustness, and output linewidth. Increasing the transmittance from 0.6% to 3.0% increases the Stokes output power and conversion efficiency but shortens the stable locking duration. Conversely, reducing the transmittance progressively narrows the Stokes linewidth. At a transmittance of about 0.2%, a Stokes linewidth of 5.70 kHz, slightly narrower than that of the pump laser, is achieved. This result indicates that low output-coupling loss extends the intracavity Stokes photon lifetime and enhances the suppression of pump-to-Stokes frequency-noise transfer, thereby enabling linewidth compression. This study reveals the role of output-coupling loss in controlling the linewidth evolution of resonantly pumped diamond Raman lasers and provides important experimental guidance for the design of low-threshold, highly stable, narrow-linewidth diamond Raman lasers.
Fourier-limited nanosecond pulses featuring narrow spectral bandwidths are required for applications in spectroscopy, sensing, and quantum optics. Here, we demonstrate a direct and simple route for the generation of single-frequency light relying on phonon-resonant Raman interactions within a monolithic diamond resonator. The technique enables the production of nearly Fourier-limited nanosecond optical pulses (15 ns), with an overall spectral bandwidth of down to 180 MHz, which is nearly two orders of magnitude narrower than the pump laser linewidth used (12 GHz). The power conversion efficiency was 47%, yielding a power spectral brightness enhancement of > 50 × compared to the pump. Our results pave the way to the integration of pulsed widely tunable, power scalable, narrow linewidth light sources into integrated photonic platforms. Furthermore, the device does not need elaborate mechanical feedback loops for cavity length or frequency stabilization, or any additional optical components.
An experimental study of normal and stimulated Raman emission in diamond is presented, including measurements of linewidth, intensity, and angular distribution of radiation having a frequency shift of 1332.0 ${\mathrm{cm}}^{\ensuremath{-}1}$. The diamond crystal formed a Raman resonator; excitation was by a giant-pulse ruby laser. The dependence of normal Stokes emission on laser intensity and the threshold for oscillation were investigated. A value for the Raman gain ($g=6.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ per MW/cm2{\mathrm{cm}}^{2}cm2) was calculated from the measured linewidth ($\ensuremath{\Delta}\ensuremath{\nu}=2.04$ ${\mathrm{cm}}^{\ensuremath{-}1}$) and cross section for scattering, and found to be in good agreement with a value determined from the threshold for oscillation. The angular distributions of anti-Stokes and Stokes emission and absorption for parallel and convergent laser light are also in good agreement with theory: The emission cone angles are strongly dependent on the angle of convergence of the incident light, and it is established that the preferred directions for emission are those making use of the most intense first-order Stokes radiation which is peaked in the forward direction within the Raman resonator.
We report low noise and narrow linewidth performance of an actively stabilized optical parametric oscillator, intracavity-pumped by a visible AlGaInP-based vertical-external-cavity surface-emitting laser (VECSEL). Under dual-locking conditions, where the VECSEL and intracavity resonant idler are stabilized using the Pound–Drever–Hall and side-of-fringe locking techniques, respectively, narrow linewidths of 6.21(1) kHz (VECSEL) and 151(1) Hz (idler) are achieved for integration times as long as 4 s, illustrating the transfer of noise from the VECSEL fundamental to the OPO non-resonant signal. In this regime, the relative intensity noise of all three interacting waves is <−120 dBc/Hz for all frequencies above 1 kHz, indicating that this coherent laser system is well-suited for quantum optics experiments, potentially those involving squeezed light generation.
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)
Tunable single-frequency lasers are essential for high-resolution spectroscopy and quantum technologies, yet achieving narrow-linewidth performance in compact, scalable systems across the UV-visible spectrum remains a key challenge. Recent work has revealed that Raman scattering in diamond can act as a natural spectral squeezer, where phonon dynamics help suppress frequency noise and concentrates optical power into a single, narrow spectral mode. Experiments at CERN and elsewhere have demonstrated linewidth compression by orders of magnitude, frequency-noise suppression exceeding 10³-10⁴, and pathways toward Schawlow–Townes-limited performance in CW regimes. These results establish Raman phonon damping as a universal mechanism for generating ultra-coherent, widely tunable lasers, opening new opportunities in quantum metrology, optical clocks, and high-resolution spectroscopy.
Tunable single-frequency lasers are essential for high-resolution spectroscopy and quantum technologies, yet achieving narrow-linewidth performance in compact, scalable systems across the UV-visible spectrum remains a key challenge. Recent work has revealed that Raman scattering in diamond can act as a natural spectral squeezer, where phonon dynamics help suppress frequency noise and concentrates optical power into a single, narrow spectral mode. Experiments at CERN and elsewhere have demonstrated linewidth compression by orders of magnitude, frequency-noise suppression exceeding 10³-10⁴, and pathways toward Schawlow–Townes-limited performance in CW regimes. These results establish Raman phonon damping as a universal mechanism for generating ultra-coherent, widely tunable lasers, opening new opportunities in quantum metrology, optical clocks, and high-resolution spectroscopy.