Inverse Spatially Offset Raman Spectroscopy And Its Application Of Non-destructive Deep Material Detection

Spatially offset Raman spectroscopy(SORS),as a new type of deep Raman spectroscopy technology,can non-invasively obtain the deep spectrum information inside diffusely scattering samples.Different from the traditional backscattering Raman spectroscopy,the principle of SORS is that the laser irradiation area and Raman spectrum acquisition area are offset by a certain distance on the sample surface.SORS has two common forms:conventional SORS and inverse SORS.In conventional SORS,the Raman spectrum is collected by concentric rings centered on the laser irradiation point,while in inverse SORS,the Raman signal is collected at the center of the ring when the laser irradiates the sample surface in the form of rings with different radii.Because inverse SORS uses a ring beam to irradiate the surface of the sample to make the illumination area larger,higher laser power can be used within the scope of the human body’s permissible illumination intensity.In addition,the technology can avoid the strong interference of fluorescence signals generated on the surface of the sample,and can accurately,quickly,non-destructive and non-label detect the multi-layer turbid media samples to obtain the deep characteristic information of the sample.Based on the principle of SORS,we developed and introduced an inverse SORS system realizing deep spectrum detection.This article’s main research is shown below:Firstly,we built the inverse SORS system,then perform rapidly and non-destructively detect the ethanol under transparent glass packaging and pig skin tissue embedded in paraffin under different spatial offsets.By selecting the Raman characteristic peaks of the surface layer(glass and Paraffin)of the sample for intensity normalization,the Raman characteristic spectra of the deep layer(ethanol and pig skin)of the sample can be obtained to identify its chemical composition.It is found that the Raman characteristic peak intensity of deep material increases with the increase of the spatial offset.The experimental results preliminarily show the correctness of the optical path system and the feasibility of inverse SORS for rapidly and non-invasive detection of deep substances in double-layer samples.Secondly,by using optical elements such as dichroic mirror and cage structures,the original optical path system was optimized and integrated,and an integrated inverse SORS spectral detection system was built.The optimized optical path system can switch the spectral detection modes by controlling the axicon,which can realize the conventional backscattering Raman spectroscopy to obtain the Raman spectrum of each layer of the sample as a reference,and can also adopt the inverse SORS to achieve the deep spectrum detection.By simply moving the axicon,the ring-shaped excitation beam is irradiated to the sample surface with a continuously changed ?s value.The system is respectively used to perform spectrum detection on the two-layer model composed of sheep scapula/paracetamol,the three-layer model composed of pig skin/silicone rubber/paracetamol,human palms and fingers.The results show that the inverse SORS can effectively avoid the interference of fluorescence signals in the surface layer,and can be widely used in deep spectral detection in multi-layer turbid media.In conclusion,the paper discusses the optical path design and application of inverse SORS.It shows that inverse SORS breaks the limitations of traditional Raman spectroscopy technology,and can obtain the deep Raman spectrum of transcutaneous bone in vivo,which provides technical support for the application of inverse SORS combined with clinical detection technology in the early diagnosis of diseases.