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Raman microlasers form on-chip versatile light sources by optical pumping, enabling numerical applications ranging from telecommunications to biological detection. Stimulated Raman scattering (SRS) lasing has been demonstrated in optical microresonators, leveraging high Q factors and small mode volume to generate downconverted photons based on the interaction of light with the Stokes vibrational mode. Unlike redshifted SRS, stimulated anti-Stokes Raman scattering (SARS) further involves the interplay between the pump photon and the SRS photon to generate an upconverted photon, depending on a highly efficient SRS signal as an essential prerequisite. Therefore, achieving SARS in microresonators is challenging due to the low lasing efficiencies of integrated Raman lasers caused by intrinsically low Raman gain. In this work, high-Q whispering gallery microresonators were fabricated by femtosecond laser photolithography assisted chemo-mechanical etching on thin-film lithium niobate (TFLN), which is a strong Raman-gain photonic platform. The high Q factor reached 4.42 × 106, which dramatically increased the circulating light intensity within a small volume. And a strong Stokes vibrational frequency of 264 cm−1 of lithium niobate was selectively excited, leading to a highly efficient SRS lasing signal with a conversion efficiency of 40.6%. And the threshold for SRS was only 0.33 mW, which is about half the best record previously reported on a TFLN platform. The combination of high Q factors, a small cavity size of 120 μm, and the excitation of a strong Raman mode allowed the formation of SARS lasing with only a 0.46 mW pump threshold. [ABSTRACT FROM AUTHOR]

Integrated Raman microlasers, particularly discrete multi‐color lasers which are crucial for extending the emission wavelength range of chip‐scale laser sources to much shorter wavelengths, are highly in demand for various spectroscopy, microscopy analysis, and biological detection applications. However, integrated multi‐color Raman microlasers have yet to be demonstrated because of the requirement of high‐Q microresonators possessing large χ(2) nonlinearity, strong Raman phonon branches, and the challenge in the cavity‐enhanced multi‐photon hyper‐Raman scattering parametric process. In this work, integrated multi‐color Raman lasers have been demonstrated for the first time at weak pump levels, via the excitation of high‐Q (> 6 × 106) phase‐matched modes in single thin‐film lithium niobate (TFLN) microresonators by dispersion engineering. Raman lasing is observed at 1712 nm for a 1547‐nm pump threshold power of only 620 µW, representing the state of the art in the TFLN platform. Furthermore, multi‐color Raman lasers are realized at discrete wavelengths of 1712, 813, 533, and 406 nm with pump levels as low as 1.60 mW, which is more than two orders of magnitude lower than the current records (i.e., 200 mW) in bulk resonators, allowed by the fulfillment of the requisite conditions consisting of broadband natural phase match, multiple‐resonance, and high‐Q factors. [ABSTRACT FROM AUTHOR]