Dynamic complex opto-magnetic holography

Computer-generated holograms with their animated, three-dimensional appearance have long appealed to our imagination as the path towards truly immersive displays with bi-directional natural parallax. Impressive progress in updateable 3-D imagery has been achieved with liquid crystal modulators and high-resolution, but quasi-static holograms are being recorded in photosensitive materials. However, the memory requirements and computational loads of real-time, large-area holography will be hard to tackle for several decades to come with the current paradigm based on a matrix calculations and bit-plane writing. Here, we experimentally demonstrate a conceptually novel, holistic approach to serial computation and repeatable writing of computer-generated dynamic holograms without Fourier transform, using minimal amounts of computer memory. We use the ultrafast opto-magnetic recording of holographic patterns in a ferrimagnetic film with femtosecond laser pulses, driven by on-the-fly hardware computation of a single holographic point. The intensity-threshold nature of the magnetic medium allows sub-diffraction-limited, point-by-point toggling of arbitrarily localized magnetic spots on the sample, according to the proposed circular detour-phase encoding, providing complex modulation and symmetrical suppression of upper diffractive orders and conjugated terms in holographically reconstructed 3-D images

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

Focal Spot, Summer 1986

https://digitalcommons.wustl.edu/focal_spot_archives/1043/thumbnail.jp

Towards compliant data retention with probe storage on patterned media

We describe how the compliance requirements for data retention from recent laws such as the US Sarbanes Oxley Act may be supported by a tamper-evident secure storage system based on probe storage with a patterned magnetic medium. This medium supports normal read/write operations by out-of-plane magnetisation of individual dots. We report on an experiment to show that in principle the medium also supports a separate class of write-once operation that destroys the out-of-plane magnetisation property of the dots irreversibly by precise local heating. The write-once operation can be used to support flexible data retention by tamper-evident writing and physical data deletion

Towards Tamper-Evident Storage on Patterned Media

We propose a tamper-evident storage system based on probe storage with a patterned magnetic medium. This medium supports normal read/write operations by out-of-plane magnetisation of individual magnetic dots. We report on measurements showing that in principle the medium also supports a separate class of write-once operation that destroys the out-of-plane magnetisation property of the dots irreversibly by precise local heating. We discuss the main issues of designing a tamper-evident storage device and file system using the properties of the medium

Creation and pinning of vortex-antivortex pairs

Computer modeling is reported about the creation and pinning of a magnetic vortex-antivortex (V-AV) pair in a superconducting thin film, due to the magnetic field of a vertical magnetic dipole above the film, and two antidot pins inside the film. For film thickness $= 0.1\xi$, $\kappa = 2$, and no pins, we find the film carries two V-AV pairs at steady state in the imposed flux range $2.10\Phi_0 < \Phi^+ < 3.0\Phi_0$, and no pairs below. With two antidot pins suitably introduced into the film, a single V-AV pair can be stable in the film for $\Phi^+ \ge 1.3\Phi_0$. At pin separation $\ge 17\xi$, we find the V-AV pair remains pinned after the dipole field is removed, and, so can represent a 1 for a nonvolatile memory.Comment: 8 pages, 6 figure