Center for Relativistic Laser Science

2018 121st KCS General Meeting

There have been various imaging techniques applying infrared (IR) light source for its advantages such as chemical selectivity, non-destructiveness, and label-free character. Recently, one of promising imaging techniques with IR light source is a photothermal microscope implementing the photothermal effect and resulting refractive index change. A mid-IR absorption of specific chemical vibration structure induce a temperature increase and refractive index changes in surrounding medium which causes the deflection of the probe beam. In our IR photothermal imaging(IPI) set-up, to enhance the spatial resolution, the non-resonant visible laser source is adopted as a probe. With high NA reflection-type objective that also enables dark-field geometry, sub-micrometer lateral spatial resolution is achieved. The spatial resolution and sensitivity of IPI microscope is determined by imaging polystyrene beads and measuring the signal intensities of ascorbic acid with varying its concentration, respectively. Unlike nonlinear optical processes, photothermal imaging can be conducted with relatively weak excitation laser power avoiding severe photo-damage in bio sample assays. Photothermal contrast images of Caenorhabditis elegans and astrocyte will be presented.