Solar sailcrafts make use of radiation pressure to propel a payload through space. Modern diffractive structures such as broadband single order gratings, polarization diffraction gratings, and related metamaterials offer the potential to replace reflective sails with efficient diffractive sails for either solar or laser driven space travel. We have experimentally verified the radiation pressure force on a transmissive diffraction grating, demonstrating a large component of force parallel to the surface of the grating. This component is important for orbit-raising types of maneuvers. Unlike a reflective sail with force components only normal to the surface, we also measure a near-vanishing normal force component around the Littrow angle
Optical Coherence Elastography (OCE) is a widely investigated noninvasive technique for estimating the mechanical properties of tissue. In particular, vibrational OCE methods aim to estimate the shear wave velocity generated by an external stimulus in order to calculate the elastic modulus of tissue. In this study, we compare the performance of five acquisition and processing techniques for estimating the shear wave speed in simulations and experiments using tissue-mimicking phantoms. Accuracy, contrast-to-noise ratio, and resolution are measured for all cases. The first two techniques make the use of one piezoelectric actuator for generating a continuous shear wave propagation (SWP) and a tone-burst propagation (TBP) of 400 Hz over the gelatin phantom. The other techniques make use of one additional actuator located on the opposite side of the region of interest in order to create an interference pattern. When both actuators have the same frequency, a standing wave (SW) pattern is generated. Otherwise, when there is a frequency difference <i>df </i>between both actuators, a crawling wave (CrW) pattern is generated and propagates with less speed than a shear wave, which makes it suitable for being detected by the 2D cross-sectional OCE imaging. If <i>df </i>is not small compared to the operational frequency, the CrW travels faster and a sampled version of it (SCrW) is acquired by the system. Preliminary results suggest that TBP (error < 4.1%) and SWP (error < 6%) techniques are more accurate when compared to mechanical measurement test results.