Nonlinear photothermal mid-infrared spectroscopy

Infrared Spectroscopic Imaging Advances as an Analytical Technology for Biomedical Sciences

“…Since the detected signal imposes a limit on the spatial frequency collected in an imaging experiment, using a visible range wavelength to detect IR contrast is an excellent illustration using photothermal imaging. − In a typical embodiment, an IR source illuminates the sample, and if there is any vibrational energy levels matching with the incident frequency, IR light is absorbed causing a thermal expansion of the material as a result of relaxation. This expansion causes a refractive index change, which can be probed through the thermal lensing mechanism using a visible laser. − The contrast, thus, is based on IR absorption, but the detected signal and spatial resolution is determined by the characteristics of visible wavelengths.…”