Stress waves propagating inside materials play a significant role in femtosecond laser processing. In this study, we measured femtosecond-laser-induced stress waves inside synthetic silica glass using a time-resolved Mach–Zehnder interferometer. A laser pulse with a wavelength of 1030 nm, pulse width of 180 fs, and pulse energy of 100 μJ was used to induce stress waves. The three-dimensional distribution of the refractive-index change of the stress wave was obtained via reconstruction using the inverse Abele transform. This result contributes to the further development of femtosecond laser processing.
Monitoring the tissue temperature is highly desirable for predictable and reproducible retinal laser therapy. We demonstrate that the temperature rise can be determined using pOCT imaging of the optical path length changes within the laser spot relative to the non-heated region. A temperature-sensitive fluorescent dye was used for initial calibration. By matching the thermal expansion across the beam width and along the full course of heating and cooling, the temperature distribution can be determined with a precision of about 10% (under 2℃ with a peak heating of 17℃) following a single laser pulse of 20ms in duration.
Laser-induced shock waves have been gaining attention for biological and medical applications in which shock waves influence cell permeation. However, the mechanisms of permeation remain mostly unclear because of the difficulty of observing the transient and dynamic behaviors of the shock waves and the cells. Here we present an all-optical measurement method that can quantitatively capture the pressure distribution of the propagating shock wave and simultaneously monitor the dynamic behavior of cell membranes. Using this method, we find that a sharp pressure gradient causes cell membrane permeation. Our measurement will further advance biological and medical applications of shock waves.
We present a method for determining the optical and thermal properties of layered materials, applicable to retinal laser therapy, using phase-resolved OCT. Transient heating of a tissue phantom is achieved by focusing a laser pulse onto a buried absorbing layer. Optical path length changes between the top of the phantom and the scattering absorbing layer induced by material expansion are extracted from the sequential B-scans. The absorption coefficient, heat conductivity and thermal expansion coefficient of the polymer are determined by matching the experimental data to a thermomechanical model of the tissue, yielding a temperature precision <2%, well below damage threshold.
We present a methodology that allows precise determination of the optical and thermal properties of layered materials using thermal perturbation and phase-resolved optical coherence tomography (pOCT). Following heating with a laser pulse of a buried absorbing layer, optical path length changes between the sample’s surface and the absorbing layer are monitored using a line-scan pOCT. Using an axisymmetric thermo-mechanical model for transversely uniform multi-layered media, we fit the absorption coefficient, the heat conductivity, and the thermal expansion coefficient of the polymer. We demonstrate that the temperature distribution can be determined with a precision under 0.1°C, after a single laser pulse.
Aerospace-grade textiles have decades of flight heritage for protection against harsh elements of the space environment. However, these substrates have remained electrically passive despite occupying useful large-area real-estate on the exterior walls of persistent spacecraft. By leveraging electronic textiles in an aerospace context, hybrid fabrics can be developed that simultaneously protect spacecraft while also detecting debris or micrometeoroid hypervelocity impactors. Specifically, this paper describes prototype development and preflight testing of piezoelectric Beta cloth ahead of a scheduled late 2020 material resiliency test on the International Space Station. Two accessible manufacturing methods for piezoelectric fiber are introduced based on modifications to piezoelectric cable that reduce diameter, increase mechanical flexibility of the fiber, and improve compatibility with textile weft insertion techniques. A Beta cloth simulant with piezoelectric fiber is introduced and custom ultra low power readout electronics are specified, which allow for a first-order power consumption estimate for scaling of this material across large-area spacecraft walls. Finally, high-velocity impact sensor data measured using the Laser Induced Particle Impact Test (LIPIT) facility is presented, building towards an accurate prediction of impactor velocity.
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