Spatially offset Raman spectroscopy (SORS) is a technique that extends traditional Raman spectroscopy by incorporating measurements at different spatial offsets. This method allows for the selective probing of subsurface layers beneath a scattering or opaque surface, making it particularly valuable in situations where traditional Raman spectroscopy might be limited by surface interference.
Key features and principles of spatially offset raman spectroscopy include:
Background: In conventional Raman spectroscopy, the scattering of light from the surface dominates the signal. This can be problematic when analyzing samples with layers beneath an obscuring surface layer or samples with strong fluorescence.
Spatial offset measurements: SORS involves collecting Raman signals at different spatial offsets or distances from the point of laser illumination. By measuring Raman scattering at various depths, information from subsurface layers can be extracted.
Depth profiling: SORS enables depth profiling without the need for physical sample preparation or removal of surface layers. This is especially advantageous for analyzing layered or turbid samples.
Mathematical models: The interpretation of SORS data often involves mathematical models that take into account the contributions from different layers at various depths. These models help to separate the signal from the surface layer and extract information from deeper layers.
Applications: Spatially offset Raman spectroscopy has found applications in various fields, including pharmaceuticals, biomedical research, art conservation, and security. In the pharmaceutical industry, for example, it can be used to analyze the content of pharmaceutical tablets without removing the packaging.
Fluorescence suppression: SORS is particularly useful in situations where fluorescence interference is a concern. By probing subsurface layers, it can help to suppress the fluorescence signal from the surface, allowing for more accurate Raman measurements.
Non-invasive depth profiling: SORS allows for non-invasive depth profiling of materials, making it suitable for analyzing complex samples without altering their structure.
Instrumentation: SORS can be implemented using specialized instrumentation that incorporates spatially offset detection optics. These instruments are designed to selectively collect Raman signals from different depths.
Spatially offset Raman spectroscopy has proven valuable in situations where conventional Raman spectroscopy faces challenges related to surface interference. It provides a non-destructive and non-invasive means of probing subsurface layers in various materials, offering insights into their composition and structure.