elastically scattered photons) featuring time-consuming spectral integration and hence a poor acquisition speed (several seconds per line or minutes per frame). This weakness constitutes a large obstacle for real-time monitoring of dynamic events in organisms. Recently, several variations of Raman spectroscopy have been developed to enhance the sensitivity of Raman spectroscopy and dynamic processes of biological samples, including coherent Raman scattering (CRS) spectroscopy and surfaceenhanced Raman spectroscopy (SERS). SERS involves a plasmonic effect where molecules absorbed on a rough metal surface can result in high Raman scattering intensities by increasing the incident electric field. [5] For SERS technology, a SERS substrate must be introduced to enhance the detection sensitivity, and the properties of the substrate (the composition, size, shape and aggregation degree of nanoparticles) affect the shape of the SERS spectra. In addition, only gold, silver, copper, and a few rare alkali metals (such as lithium and sodium) have strong SERS effects, and it is necessary to effectively solve the biocompatibility and safety issues in the preparation of nanomaterials. With the development of laser and nonlinear optics, CRS microscopy has also been demonstrated to break the speed limit for vibrational imaging. [6] CRS has two major forms: coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS); [7] both techniques can dramatically increase the Raman signal by a few orders of magnitude and hence are able to achieve video-rate molecular imaging in vivo. [8,9] CARS and SRS processes often exist in a sample concurrently because of the same excitation conditions (spatiotemporal overlap of the pump and Stokes beam) with a frequency difference (Raman shift) matching the molecular vibrational frequency. However, CARS is an optical parametric process accompanied by a nonresonant part originating from fourwave mixing processes. This intrinsic nonresonant background results in a deviation or even distortion of the Raman spectrum. SRS is a direct process of photon-vibration energy transfer: in brief, the interaction between the electron cloud of a sample and the photons of two lasers creates an induced dipole moment within the molecule based on its polarizability, resulting in a pump energy loss (stimulated Raman loss, SRL) and a Stokes energy increase (stimulated Raman gain, SRG). The Raman signal can, therefore, be deduced from SRL or SRG, resulting in a high-fidelity Raman spectrum free from the nonresonant background. Moreover, the SRS signal exhibits Stimulated Raman scattering (SRS) microscopy is a nonlinear optical imaging method for visualizing chemical content based on molecular vibrational bonds. Featuring high speed, high resolution, high sensitivity, high accuracy, and 3D sectioning, SRS microscopy has made tremendous progress toward biochemical information acquisition, cellular function investigation, and label-free medical diagnosis in the biosciences. In this review, the principle of ...