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.
Photoplethysmography (PPG) is an optical technique that monitors oxygen saturation levels that is captured by pulse oximeters and some wearables such as smartwatches. The technique has been shown to overestimate oxyhemoglobin saturation in patients with darker skin, potentially leading to silent hypoxia and a disproportionately higher number of deaths in black and brown COVID-19 patients. We demonstrate a novel PPG technique that uses radially polarized light created by light-emitting diodes (LEDs) to address this problem. Our method performs single-shot, multiple polarization measurements using a single wavelength. We present a new use for vector-beams as well as the first demonstration of vector-beam generation using LEDs.
In this work, we study the self-healing properties of the space-time (ST) light sheet upon interaction with a partially transparent object, namely a microtissue array of biological samples. In particular, we study the response of the ST light sheet upon encountering biological tissues that have been graded as normal (benign), malignant, and malignant tumor stage III. We find a differential response that can be leveraged for characterization of the tissue specimens. Specifically, the ST light sheet is observed to more completely reconstruct upon traversing the normal tissue compared to the malignant specimens. We believe that this is the first report exploring the potential of self-healing as a metric for tissue characterization.
We report more than two octave spanning mid-IR flat-top supercontinuum (SC) generation using all normal As2S5-borosilicate hybrid photonic crystal fiber. Our design is based on a chalcogenide As2S5 photonic crystal fiber (PCF), where the first ring composed of six air holes is made by borosilicate glass. By injecting 50-fs pulses with 1.6 nJ energy at 2.5 μm in the all normal dispersion (ANDi) regime, a flat-top broadband SC extending from 1 to 5 μm with high-spectral flatness of 8 dB is obtained in only 4-mm fiber length. To the best of our knowledge, we present the broadest flat mid-IR spectrum generated in the ANDi regime of an optical fiber. The self-phase modulation and the optical wave breaking are identified as the main broadening mechanisms. The obtained broadband light source can be potentially used in the field of spectroscopy and in high-resolution optical coherent tomography owing to the high-spectral SC flatness generated by our designed fiber.
We numerically demonstrate the supercontinuum (SC) generation in a novel chalcogenide As2S5 nanowire embeddedcore into Tellurite photonic crystal fiber (PCF). This hybrid As2S5-tellurite small core PCF has a pitch of 0.7 μm and air hole diameter of 0.2 μm. It exhibits a zero dispersion wavelength (ZDW) of 3.25 μm with an overall highly engineered group velocity dispersion (GVD) shifted to the mid-IR wavelengths region. By injecting 100 fs hyperbolic-secant input pulses delivered by available tunable optical parametric oscillator (OPO) system at the pump wavelength of 3.389 μm, we obtain a broadband coherent mid-IR SC generated in only 1 mm-long PCF with a peak power of 8.8 kW. An ultralarge mid-IR bandwidth extending from 1000 to 7200 nm is generated with more than 60% of the total power which is available beyond 3 μm. The proposed hybrid PCF structure shows to be very promising for designing new compact, stable and powerful SC fiber laser sources in the long mid-IR wavelength region.
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