Application of a high power Yb fiber‐based laser compatible with commercial optical parametric oscillator for coherent anti‐stokes raman scattering microscopy

Abstract

Coherent anti-Stokes Raman scattering (CARS) microscopy is a powerful tool for chemical analysis at a subcellular level, frequently used for imaging lipid dynamics in living cells. We report a high-power picosecond fiber-based laser and its application for optical parametric oscillator (OPO) pumping and CARS microscopy. This fiber-based laser has been carefully characterized. It produces 5 ps pulses with 0.8 nm spectral width at a 1,030 nm wavelength with more than 10 W of average power at 80 MHz repetition rate; these spectral and temporal properties can be slightly modified. We then study the influence of these modifications on the spectral and temporal properties of the OPO. We find that the OPO system generates a weakly spectrally chirped signal beam constituted of 3 ps pulses with 0.4 nm spectral width tunable from 790 to 930 nm optimal for CARS imaging. The frequency doubling unconverted part is composed of 7-8 ps pulses with 0.75 nm spectral width compatible with CARS imaging. We also study the influence of the fiber laser properties on the CARS signal generated by distilled water. In agreement with theory, we find that shorter temporal pulses allow higher peak powers and thus higher CARS signal, if the spectral widths are less than 10 cm(-1) . We demonstrate that this source is suitable for performing CARS imaging of living cells during several hours without photodamages. We finally demonstrate CARS imaging on more complex aquatic organisms called copepods (micro-crustaceans), on which we distinguish morphological details and lipid reserves.

Label-free microscopy and stress responses reveal the functional organization of Pseudodiaptomus marinus copepod myofibrils

“…4a), as described in our preliminary studies on P. marinus (Hage et al, 2014) and in studies on human and mice muscles (Brackmann et al, 2010). Micron sized spots were assigned to subsarcolemmal mitochondria based on their morphology and on their superposition with the spots observed on a TPEF image of the same optical section ( Fig.…”

“…For the sake of comparison, CARS images were obtained together with SHG images on a home-made set up using a high power picosecond fiber-based laser described elsewhere (Hage et al, 2014). This setup provided a fixed 1030 nm beam which was used as the Stokes beam and a tunable beam from an OPO.…”

“…The nonresonant CARS signal measured at 2800 cm À1 was one order of magnitude lower than the CARS signal; it therefore introduced no artifact into our analysis. During CARS imaging no significant fluorescence was generated along with the CARS signal as previously described (Hage et al, 2014). On this CARS setup, flavin autofluorescence was collected between 630 and 670 nm upon two-photon excitation at 796 nm.…”