| 1. |
- Glimtoft, Martin, et al.
(författare)
-
Digital micromirror devices in Raman trace detection of explosives
- 2016
-
Ingår i: Detection and Sensing of Mines, Explosive Objects, and Obscured Targets XXI. - : SPIE - International Society for Optical Engineering. - 9781510600645
-
Konferensbidrag (refereegranskat)abstract
- Imaging Raman spectroscopy based on tunable filters is an established technique for detecting single explosives particles at stand-off distances. However, large light losses are inherent in the design due to sequential imaging at different wavelengths, leading to effective transmission often well below 1 %. The use of digital micromirror devices (DMD) and compressive sensing (CS) in imaging Raman explosives trace detection can improve light throughput and add significant flexibility compared to existing systems. DMDs are based on mature microelectronics technology, and are compact, scalable, and can be customized for specific tasks, including new functions not available with current technologies. This paper has been focusing on investigating how a DMD can be used when applying CS-based imaging Raman spectroscopy on stand-off explosives trace detection, and evaluating the performance in terms of light throughput, image reconstruction ability and potential detection limits. This type of setup also gives the possibility to combine imaging Raman with non-spatially resolved fluorescence suppression techniques, such as Kerr gating. The system used consists of a 2nd harmonics Nd:YAG laser for sample excitation, collection optics, DMD, CMOS-camera and a spectrometer with ICCD camera for signal gating and detection. Initial results for compressive sensing imaging Raman shows a stable reconstruction procedure even at low signals and in presence of interfering background signal. It is also shown to give increased effective light transmission without sacrificing molecular specificity or area coverage compared to filter based imaging Raman. At the same time it adds flexibility so the setup can be customized for new functionality.
|
|
| 2. |
- Svanqvist, Mattias, et al.
(författare)
-
Non-jellium scaling of metal cluster ionization energies and electron affinities
- 2010
-
Ingår i: EUROPEAN PHYSICAL JOURNAL D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 56:2, s. 199-203
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental literature data on ionization energies and electron affinities of metal clusters are reviewed and analyzed in terms of an expansion in the inverse cluster radius. The coefficient of the finite size correction for ionization energies decreases with increasing bulk work function whereas the corresponding coefficient for electron affinities decreases. This sharply contrasts the predictions based both on density functional theory of spherical jellium clusters and on classical electrostatics. A scaling of the coefficient for the ionization potentials with the atomic radius yields a linear behavior which extrapolates to zero around 6 eV.
|
|
| 3. |
- Svanqvist, Mattias, et al.
(författare)
-
Stand-off detection of explosives and precursors using compressive sensing Raman spectroscopy
- 2016
-
Ingår i: Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XVII. - : SPIE - International Society for Optical Engineering. - 9781510600652
-
Konferensbidrag (refereegranskat)abstract
- We present initial results on the performance of a compressive sensing setup for Raman imaging spectroscopy for standoff trace explosives detection. Hyperspectral image reconstruction is demonstrated under low signal conditions and successful spatial separation of substances with close lying Raman peaks is shown.
|
|
| 4. |
- Terschlüsen, Joachim Andreas, et al.
(författare)
-
Measuring the temporal coherence of a high harmonic generation setup employing a Fourier transform spectrometer for the VUV/XUV
- 2014
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 768, s. 84-88
-
Tidskriftsartikel (refereegranskat)abstract
- In this experiment we used an 800 nm laser to generate high-order harmonics in a gas cell filled with Argon. Of those photons, a harmonic with 42 eV was selected by using a time-preserving grating monochromator. Employing a modified Mach–Zehnder type Fourier transform spectrometer for the VUV/XUV it was possible to measure the temporal coherence of the selected photons to about 6 fs. We demonstrated that not only could this kind of measurement be performed with a Fourier transform spectrometer, but also with some spatial resolution without modifying the XUV source or the spectrometer.
|
|
| 5. |
- Vuckovic, Sasa, 1974, et al.
(författare)
-
Laser ablation source for formation and deposition of size-selected metal clusters
- 2008
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:7
-
Tidskriftsartikel (refereegranskat)abstract
- This work describes construction of a source and optimisation of its parameters for production of cluster ion beams using material ablation by the second harmonic of a Nd:YAG laser (532 nm). The influence of different source parameters such as carrier gas pressure, laser power, delay time between gas, and laser pulses as well as nozzle configuration on the cluster formation are studied. For the current experiments the laser ablation cluster source was optimized for production of Co cluster ions. Clusters with n up to 150 atoms are registered by a time-of-flight mass spectrometer. Deposition of size-selected Co50 clusters with kinetic energies in the interval of 250–4850 eV/cluster on highly ordered pyrolytic graphite is studied. At the highest impact energies the clusters are implanted. Craters and well-like structures can be seen by scanning tunneling microscopy at impact spots. A decrease in cluster kinetic energy leads to formation of bumplike structures which probably represent damaged graphite areas with incorporated Co atoms. Further decrease in the cluster impact energy to the level of 450–250 eV/cluster creates condition for so-called cluster pinning when the cluster constituents are intact but the energy transferred to the graphite is still enough to produce radiation defects to which the cluster is bound.
|
|
