Optical Photothermal Infrared, or O-PTIR, is using a visible laser and detector, to overcome the main limitation of a traditional FTIR microscope. An FTIR microscope has a spatial resolution dependant on the wavelength. OPTIR’s visible laser’s wavelength (532nm) is co-aligned with the IR laser, exciting the sample, resulting in an IR response based on the IR absorption of the sample. Because the visible laser is also used for detection, the IR response can be measured at the same spatial resolution as the 532nm wavelength visible laser.
A schematic diagram of O-PTIR is shown below:
Standard FTIR techniques are limited in spatial resolution due to their wavelength dependency. By using a visible laser as a detection method for the IR absorption of a sample, the spatial resolution of the O-PTIR instrument is limited to the wavelength of the visible laser that is used. In the mIRage instruments, a 532nm green visible laser is used, resulting in a maximum spatial resolution of 532 nanometer.
This technique allows for research on a much smaller scale than traditional FTIR microscopes. Now, instead of bulk measurements, a localized measurement can be performed, resulting in more precise, and even more detailed information.
When measuring a homogeneous sample in reflection mode, the spectra from transmission FTIR and O-PTIR will correllate perfectly. Differences in resulting spectra, may be from unexpected inhomogeneity of the sample.
The O-PTIR microscopes are designed to be very flexible. It is very easy to add a Raman laser and detector, and do co-located Raman+O-PTIR microscopy. With the latest mIRage-LS, it is now even possible to do Fluorescence at the exact same spot, all combined in one instrument.