Femtosecond Photoelectron Point Projection Microscope

By utilizing a nanometer ultrafast electron source in a point projection microscope we demonstrate that images of nanoparticles with spatial resolutions of the order of 100 nanometers can be obtained. The duration of the emission process of the photoemitted electrons used to make images is shown to be of the order of 100 fs using an autocorrelation technique. The compact geometry of this photoelectron point projection microscope does not preclude its use as a simple ultrafast electron microscope, and we use simple analytic models to estimate temporal resolutions that can be expected when using it as a pump-probe ultrafast electron microscope. These models show a significant increase in temporal resolution when comparing to ultrafast electron microscopes based on conventional designs. We also model the microscopes spectroscopic abilities to capture ultrafast phenomena such as the photon induced near field effect

Low Energy Electron Point Projection Microscopy of Suspended Graphene, the Ultimate "Microscope Slide"

Point Projection Microscopy (PPM) is used to image suspended graphene using low-energy electrons (100-200eV). Because of the low energies used, the graphene is neither damaged or contaminated by the electron beam. The transparency of graphene is measured to be 74%, equivalent to electron transmission through a sheet as thick as twice the covalent radius of sp^2-bonded carbon. Also observed is rippling in the structure of the suspended graphene, with a wavelength of approximately 26 nm. The interference of the electron beam due to the diffraction off the edge of a graphene knife edge is observed and used to calculate a virtual source size of 4.7 +/- 0.6 Angstroms for the electron emitter. It is demonstrated that graphene can be used as both anode and substrate in PPM in order to avoid distortions due to strong field gradients around nano-scale objects. Graphene can be used to image objects suspended on the sheet using PPM, and in the future, electron holography

Maximum RMS error comparison of several redundancy techniques

Paper presents mathematical comparison of several techniques with the limiting slope technique for data reduction and reconstruction. Limiting slope method results in maximum possible RMS error versus data compression ratio advantage of 2-to-1 over step and fan methods and 3-to-1 over the two point projection method

A New Fluid-Structure Interaction Point-Projection Method

A new point-projection method was developed to transfer loads and displacements in a two-way coupled fluid-structure interaction problem. The existing method involved projecting the load at each computational fluid dynamics (CFD) node onto a corresponding computation structural dynamics (CSD) element. The load is distributed to the CSD nodes on that element. However, the solution is not unique and will vary the projection. In the new method, a rigid pyramid element is built upon the CSD element and that encompasses the CFD node. Thus, the CFD load will be uniquely distributed to the CSD nodes. After the CSD code updates the CSD node location, the pyramid element can also be used to update the location of the CFD node. This work describes a FORTRAN routine that coupled LS-DYNA to Loci/BLAST and tests conducted to test the validation, work conservation, and robustness of the routine