Current optical data storage (ODS) technologies use onephoton-absorption processes to write data by locally changing the optical properties of the medium. [ 1 , 2 ] Since the lateral dimensions of spots that can be written are near the diffraction limit, signifi cant capacity increases require new approaches such as storage in three dimensions. DVDs, which comprise up to four individually addressable storage layers, exemplify the potential of this concept, but the complexity of producing and using multilayer systems increases with the number of layers. In bulk materials, changes can be confi ned in the third dimension via nonlinear optical processes, such as two-photon absorption (TPA). [3][4][5][6] We have developed a novel ODS system that relies on the optically-induced switching of the aggregation state and fl uorescence of a TPA dye in a polymer matrix. Welldefi ned, ∼ 3 × 3 × 6 μ m-large voxels were written with single focused laser pulses and read by confocal laser scanning microscopy. Such ODS systems are easily produced and promise a storage capacity of up to several Tbytes on a DVD-size disk, which is ∼ 100× higher than that of current commercial ODS technologies. [ 6 , 7 ] The optical changes considered for rewritable and write-once read-many three-dimensional (3D) ODS storage media based on TPA include reversible and irreversible photo chemical reactions such as photoisomerizations, [8][9][10] photo-induced dimerizations, [ 11 , 12 ] photodecompositions, [ 13 , 14 ] and photopolymerizations. [15][16][17] Fluorescent photochromic systems have attracted particular interest, because the exploitable photophysical processes are fast, effi cient, and reversible. [18][19][20] However, it has been challenging to create fl uorescent photochromic materials, which combine high stability, high fl uorescence quantum yield, and large TPA cross-section. We here demonstrate a novel approach to 3D ODS materials, which relies on the switching of the aggregation state of an excimer-forming fl uorescent dye with an appreciable TPA cross-section in an inert host polymer.We have previously reported a range of materials, which change their fl uorescence and/or absorption properties upon exposure to heat, [21][22][23] chemicals, [ 24 ] or mechanical forces, [25][26][27] on account of reversible or irreversible stimulusinduced changes of the aggregation state of the dye molecules. We surmised that such changes could be induced in small volumes by TPA-induced local heating and therefore explored a melt-processed blend of poly(ethylene terephthalate glycol) (PETG) and 1.1% w/w of 1,4-bis( α -cyano-4-octadecyloxystyryl)-2,5-dimethoxybenzene [ 22 , 23 ] (C18-RG, Figure 1 a) as TPAaddressable ODS medium. C18-RG was selected on account of its signifi cant changes in absorption and emission spectra upon aggregation/dissociation, its high thermal and photochemical stability, and, as demonstrated here, its appreciable TPA cross-section. PETG was chosen as the matrix due to its glassy nature and transparency in the relevant op...
The aim of this project is to integrate a large solid-angle detector array and a high speed pipelined parallel processing engine, with an embedded implementation of the Dynamic Analysis (DA) method for fluorescence spectra deconvolution and image projection, to yield a detection system capable of overlap-resolved real-time elemental imaging at up to ~10 7 events per second.The detector array comprises a 384 element low-leakage Si pad array ( Fig. 1) under development at BNL [1,2], with integrated low-noise preamplifier, a high order shaper with baseline stabilizer, multiplexed 12 bit ADC and over-threshold TDC to enable pile-up detection and rejection. The array is wire-bonded to 12 signal processing chips, which are water cooled with additional Peltier cooling of the detector array to -35 °C. A prototype of the detector array has recently demonstrated an energy resolution of 184 eV (The DA method builds a matrix transform to perform the task of spectral deconvolution of overlapping element spectra, including fluorescence lines and detector artefacts, such as tailing and escape peaks [4]. The method was originally developed at the CSIRO to project quantitative elemental images derived from proton induced X-ray emission (PIXE) data and has been recently extended to handle Synchrotron X-ray Fluorescence (SXRF) data [5]. The DA approach lends itself to real-time processing of detected X-ray counts on an event-by-event basis. Each event is tagged by detector number and current XY position of the sample stage for imaging (and potentially E and θ for spectroscopy and tomography). The detector number is used to select DA terms appropriate to the take-off geometry of the detector element, and these terms are accumulated into the pixel selected by the associated XY tag. This close coupling of scan coordinates with data acquisition removes the common constraint of ~second dwell time per pixel, enabling high definition images to be collected. Image sizes of 500 x 500 pixels or more at dwells down to 1 ms or less are envisaged.The parallel processing engine has been developed at the CSIRO for machine vision applications and consists of a wide input data interface, 150 MHz FPGA connected to 3 large static RAMs, Motorola PowerPC co-processor, and ample fast serial (8 x 11.1Gb/s) and Ethernet ports (2 x 1Gb/s, 1 x 100Mb/s). Code for the FPGA is developed using an in-house pipelined, parallel processing compiler called 3PL, and will handle pile-up rejection, energy calibration mapping and DA projection. The PowerPC will handle image accumulation and display and external control requests as an EPICS control node. A 155 bit I/O card will reside near the detector array and interface to the parallel processing card, located outside the hutch, via a high-speed fibre-optic link; the detector and I/O card will occupy minimal end-station real-estate.Our goal is to have this detector system adopted for high performance imaging at the NSLS and on the Microspectroscopy beam-line (BL9) of the Australian Synchrotron [6].
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