Space-time wave packets are a class of pulsed optical beams that are diffraction-free and dispersion-free in free space by virtue of introducing a tight correlation between the spatial and temporal degrees of freedom of the field. Such wave packets have been recently synthesized in a novel configuration that makes use of a spatial light modulator to realize the required spatio-temporal correlations. This arrangement combines pulse-modulation and beam-shaping to assign one spatial frequency to each wavelength according to a prescribed correlation function. Relying on a spatial light modulator results in several limitations by virtue of their pixelation, small area, and low energy-handling capability. Here we demonstrate the synthesis of space-time wave packets with one spatial dimension kept uniform - that is, light sheets - using transparent transmissive phase plates produced by a gray-scale lithography process. We confirm the diffraction-free behavior of wave packets having a bandwidth of 0.25 nm (filtered from a typical femtosecond Ti:sapphire laser) and 30 nm (a multi-terawatt femtosecond laser). This work paves the way for developing versatile high-energy light bullets for applications in nonlinear optics and laser machining.
Many geometric quantities can be computed efficiently for convex meshes. For general meshes, methods for approximate convex decomposition have been developed that decompose a static, non-convex object into a small set of approximately convex parts. The convex hulls of those parts can then be used as a piecewise convex approximation to the original mesh.
While previous work was only concerned with static meshes, we present a method for decomposing animated 3D meshes into temporally coherent approximately convex parts. Given a mesh and several training frames---that is, different spatial configurations of its vertices---we precompute an approximate convex decomposition that is independent of any specific frame. Such a decomposition can be transferred in real-time to novel, unseen frames. We apply our method to a variety of pre-animated meshes as well as a 3D character interactively controlled by a user's body pose. We further demonstrate that our method enables real-time physics simulations to interact with animated meshes.
Single-shot, tomographic imaging of the three-dimensional concentration field is demonstrated in a turbulent gaseous free jet in co-flow using volumetrically illuminated laser-induced fluorescence. The fourth-harmonic output of an Nd:YAG laser at 266 nm is formed into a collimated 15 × 20 mm2 beam to excite the ground singlet state of acetone seeded into the central jet. Subsequent fluorescence is collected along eight lines of sight for tomographic reconstruction using a combination of stereoscopes optically coupled to four two-stage intensified CMOS cameras. The performance of the imaging system is evaluated and shown to be sufficient for recording instantaneous three-dimensional features with high signal-to-noise (130:1) and nominal spatial resolution of 0.6-1.5 mm at x/D = 7-15.5.
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