Long-term Brillouin imaging of live cells with reduced photodamage at 660nm wavelength

Brillouin microscopy is an all-optical, non-contact method for characterizing mechanical properties of materials by measuring the spectrum of light which scatters from spontaneous (thermally induced) density waves inside a material. Due to the weak efficiency of the scattering, for Brillouin imaging of live samples, photodamage imposes a significant limitation on both speed and the SNR. To overcome this barrier, we evaluated Brillouin microscopy at different illumination wavelengths. We show that red wavelengths represent the best compromise between scattering efficiency (proportional to λ^-4) and minimal photodamage. We demonstrate that a Brillouin microscope based on 660 nm laser has a significantly higher limit on illumination powers that can be used to image live cells due to the reduced photodamage of 660 nm light, compared to standard 532 nm lasers. Low photodamage allows for longer integration times or using higher power without damaging live samples. This opens doors for improved accuracy and/or higher speed Brillouin imaging of live biological samples.