Optica 6, 385–388 (2019)

While it is known that third-harmonic generation (THG) microscopy can probe birefringence and molecular ordering, thanks to its inherent polarization sensitivity, this feature has now been exploited for live biological imaging applications as the technique’s response time is slow. Now, Joséphine Morizet and colleagues from France have come out with a fast polarization-resolved THG microscope (P-THG) that offers temporal resolution in the 10-ms range. They use an electro-optic modulator to switch the excitation polarization within 12 µs between every line scan and developed a fit-free methodology based on the calculation of the Fourier components of P-THG signals. To prove that their approach is feasible, the team carried out measurements on molecular ordering in deforming lipid structures, in vivo detection of the anisotropy of flowing microparticles in the zebrafish’s inner ear, and one-shot detection of birefringence from ordered lipids and biocrystals in live organisms.

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The Optical Society