Progress In recent years, researchers have done lots of work on improving the imaging performance of confocal Raman spectroscopy. Under far-field optical conditions, the following three types of technologies are mainly used: High-resolution laser confocal Raman spectroscopy technology based on image restoration, this type of method is based on the existing confocal Raman spectroscopy system to perform image restoration processing on the detected Raman spectroscopy images to improve system resolution; High-resolution laser confocal Raman spectroscopy technology based on optical structure modulation, this type of method mainly uses spatial modulation technology to modulate the incident light or collected light beam to improve the system resolution; High-resolution laser confocal Raman spectroscopy technology based on far-field optical profilometry, this type of technology mainly improves the system resolution by combining other optical profilometry methods with laser confocal Raman spectroscopy, and realizes multidimensional detection of topographic and spectral information. However, the above methods have the following problems: limited by the fluctuation of the sample surface, leading low the signal-to-noise ratio of the original degraded image, and low accuracy and authenticity of the restoration result; heavy loss of light intensity signal, and complicated system structure; low correspondence of topographic and spectra information, and the low focusing ability.This paper overviews our series of work on laser differential confocal Raman spectroscopy, which improving the spatial resolution, spectral imaging capability, scanning imaging speed, and stray light suppression of the confocal Raman spectroscopy. Laser differential confocal Raman microscopy, a technique fusing differential confocal microscopy and Raman spectroscopy, realizes the point-to-point collection of three-dimensional nanoscale topographic information with the simultaneous reconstruction of corresponding chemical information, and improves the axial focusing resolution to 1 nm. Radially polarized differential confocal Raman spectroscopy improves lateral resolution to 240 nm by compressing the diameter of the incident spot. Laser dual differential confocal Raman rapid spectroscopy increases the sensing measurement range to 0.54 µm, achieving high-precision measurement of surface profile without axial scanning. Laser divided-aperture differential/dual differential confocal Raman microscopy suppresses background noise interference and improves stability. Laser differential correlation-confocal Raman microscopy improves lateral and axial resolutions of Raman mapping by 23.1% and 33.1%, respectively, compared with the confocal Raman spectroscopy. Based on the above methods, we established a series of laser differential confocal Raman spectroscopic instruments.Conclusions and Prospects With the increasing demand of modern technology for the miniaturization of the measured target and the complexity of the measured information, laser confocal Raman microscopy is also facing more and more serious challenges in the detection performance of the micro-nano region. High-performance laser confocal Raman spectroscopy with high resolution and multi-dimensional information detection capabilities provides a way to ensure the key role of Raman spectroscopy in cutting-edge researches.

Raman spectroscopy is already widely used as an analytical tool in a broad range of applications, due to its characteristics of molecular fingerprint, label-free, sample preparation-free, small sample amount, and non-invasive. As the introduction of confocal microscopy, laser confocal Raman spectroscopy has inherited the unique "molecular fingerprint" characteristics of Raman spectroscopy and the high-resolution tomographic imaging characteristics of confocal microscopy, making laser confocal Raman spectroscopy plays an important role on exploring the microscopic molecular world, and has gradually become an indispensable analysis and detection method in the fields of physical chemistry, manufacturing, archeology and geology, semiconductor, advanced materials, and biomedicine. However, with the in-depth research on nano-microscopic regions such as semiconductor devices and single-cell imaging, the requirements for confocal Raman spectroscopy are strict. At present, there are fundamental issues such as low spatial resolution and the simultaneous detection of geometric shape and spectral information, which limit confocal Raman spectroscopy's wider application to nanoscale sciences. Therefore, it has a great significance to handle these limitations to expand its application field.