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Diamond Raman Lasers Push the Limits of Tunability and Coherence

Eduardo Granados, Zhenxu Bai

Published Aug 26, 2025• 0 citations
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Abstract

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.

DOI
10.1364/opticaopen.29978653.v1

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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.
Fourier-limited and tunable nanosecond pulses are essential for applications that rely on high-intensity interactions between light and atoms. These applications require precise and wide tunability across a large range of wavelengths (expanding from the UV to the near-IR). The vast interest in producing and integrating pulsed tunable narrow linewidth light is further fuelled by applications in quantum technology. The main challenge here is in the production of many (hundreds to thousands) individually tunable, narrow-band pulses simultaneously. Photonic integrated circuits (PICs) are expected to provide the scalability and simplicity required for these quantum technology-based sensing systems and applications, but there are still many obstacles to overcome. Among these are improvements in active materials, such as direct gain and laser output in the green-yellow spectral range.
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.
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.
This is the first reported observation of a second-order Raman spectrum by means of coherent Raman spectroscopy. Optically heterodyned Raman-induced Kerr-effect spectroscopy was used to study the two-phonon Raman peaks of a highly fluorescent sample of diamond with sensitivity exceeding that obtained in spontaneous scattering or other forms of coherent Raman techniques. The frequency of the one-phonon peak was measured to be 1333.1 +/- 0.5 cm(-1). The frequency of the sharp two-phonon peak was measured to be 2668.6 +/- 0.5 cm(-1), in agreement with lower-resolution spontaneous-scattering measurements.
High-Resolution In-Source Spectroscopy Integrated tunable diamond Raman lasers offer vital access to the hyperfine structure of atoms, becoming essential in scalable ion-based quantum technologies. Exploiting the Raman effect, the device produces spectrally-bright tunable Stokes pulses, showcasing MHz-class resolution without active cavity stabilization (see article 2300564 by Eduardo Granados and co-workers). This study demonstrates the efficacy of these lasers as a tool for high-resolution in-source spectroscopy, paving the way for numerous applications in the fields of atomic and nuclear physics.