Submicron Simultaneous IR and Raman Microscopy (IR+Raman): Breakthrough Developments in Optical Photothermal IR (O-PTIR) combined with Raman Provide New Capabilities

Both Infrared (IR) and Raman Spectroscopies are well established, relatively mature technologies and are typically present as separate stand-alone instruments in most laboratories, since each technique offers unique analytical capabilities with complimentary spectroscopic information.
The recent advent of Optical Photothermal IR (O-PTIR), which has enabled for the first time, submicron infrared microscopy in reflection mode (far-field) providing “FTIR transmission-like” spectral quality, without the typical reflection spectral artefacts and distortions associated with traditional FTIR or other emerging QCL based IR microscopy systems.
The fundamental basis for the technique, the “IR Photothermal Effect” is not new and has been exploited for decades with techniques such as PhotoAcoustic Spectroscopy (PAS) and more recently with AFM-IR (nano-IR). Where O-PTIR differs to these other Photothermal techniques is that it uses an optical (green laser) probe for detection, being analogous to the microphone in PAS and the AFM tip in AFM-IR. The use of this optical probe is the key enabling breakthrough in O-PTIR allowing for non-contact, far-field measurements, which provides for numerous benefits in instrument capabilities relative to traditional FTIR/QCL microscopy but also in instrument architecture, thus allowing, in a world first, a combined IR and Raman (IRaman) platform that provides for simultaneous IR and Raman spectral information at the same time, from the same spot with the same spatial resolution
Fig 1 (right) demonstrates the well-known complementarity of the IR and Raman, where certain bands are active or strong with one technique and not in the other, thus a simultaneous collection provides for significantly more information and better sample characterisation and also opens up new data analysis strategies for these two correlative techniques. Polymeric examples as well as examples from life sciences, pharmaceutical and industrial failure analysis will be presented.