Optical tweezers (OT) has proven to be an indispensable tool for elucidating phenomena in colloidal physics and for biomedical applications. Additionally, OT has been used to apply sub-piconewton forces on microscopic particles, for example in cells, as well as to measure displacements with nanometer resolution to extrapolate mechanical properties. Recently, an OT platform based on light sheet microscopy with a continuous wave laser has been developed to trap microscopic dielectric particles. However, the reduced gradient force resulting from the light sheet intensity distribution produces a trap stiffness an order of magnitude lower than its traditional circularly symmetric Gaussian counterpart. As a result, a high laser power, on the order of 50 mW is required, which risks phototoxicity for biological applications. In this work, we first compare the trap stiffnesses of continuous wave and femtosecond pulsed laser sources on dielectric particles in sub-1 mW scale. Next, we demonstrate the OT of dielectric spheres using a flat-top light sheet generated by a femtosecond pulsed laser source utilizing average powers as low as 1 mW. We propose leveraging flat-top light sheet OT to characterize the local and average mechanical properties of biological specimens.
In this work, we compare the performance of a quantitative scientific complementary metal-oxide semiconductor
(qCMOS) camera to the sCMOS camera for multiphoton imaging of tissue specimens. We find that the qCMOS
achieves a signal-to-background ratio that is ~2x and ~1.6x higher than that achieved by the sCMOS for twophoton
fluorescence and second-harmonic generation (SHG) imaging, respectively. The field-of-view of the
qCMOS camera is noticeably larger at ~1.3x that of the sCMOS. We also confirm that the qCMOS can spatially
resolve features as fine as 12.5 μm in 200-μm thick tendon tissue, at a penetration depth of 140 μm, using SHG
imaging. Our results highlight the applicability of the qCMOS for some multiphoton imaging applications.
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