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71.
This paper reports on the experimental observation of the displacement of a surface plasmon resonance (SPR) excited by a metallic diffraction grating. This effect is achieved by the use of an electro-optical material composed of nano-sized droplets of liquid crystals dispersed in a host polymer. The average refractive index of this material in the form of a thin film on the undulated metal surface can be modified with the application of an external electric field and to tune the wavelength at which the SPR excitation leads to a reflection minimum. The theoretical design and experimental demonstration of the principle of this component are described. 相似文献
72.
Laser plasma thruster 总被引:5,自引:0,他引:5
Luke J.R. Phipps C.R. McDuff G.G. 《Applied Physics A: Materials Science & Processing》2003,77(2):343-348
The laser plasma thruster (LPT) is a new microthruster for small satellites. We report on development and testing of a prototype
LPT. Some advantages of the LPT are: thruster voltage 4 V, mass less than 1 kg, power-to-thrust ratio 10 kW/N, and Isp up to 1000 s. Typical thrust level is 250 μN with PVC fuel. Thrust of 1 mN is expected with energetic fuel. The pre-prototype
continuous-thrust experiment includes the laser mount and heat sink, lens mounts, and focusing mechanism, which are coupled
to the target-material transport mechanism. The target material is applied to a transparent plastic tape, and the laser is
focused on a series of tracks on the tape. The tape-drive hardware and laser-drive electronics are described. Design, construction,
and calibration of the thrust stand are described. During continuous operation, the exhaust plume is deflected in the direction
of the moving tape. When the laser is operated in pulsed mode, the exhaust plume is perpendicular to the tape (parallel to
the optical axis). This provides some thrust-vector control. Measured thrust is 70 μN with PVC fuel, and 550 μN with energetic
fuel, with a specific impulse of 350 s.
Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +1-505-272-7203, E-mail: luke@iera.nmt.edu 相似文献
73.
Deep drilling of metals by femtosecond laser pulses 总被引:3,自引:0,他引:3
G. Kamlage T. Bauer A. Ostendorf B.N. Chichkov 《Applied Physics A: Materials Science & Processing》2003,77(2):307-310
Results of recent investigations on deep drilling of metals by femtosecond laser pulses are reported. At high laser fluences,
well above the ablation threshold, femtosecond lasers can drill deep, high-quality holes in metals without any post-processing
or special gas environment. It is shown that for high-quality drilling of metals, the following processes are important: (1)
laser-induced optical breakdown of air containing metal vapor and small metal particles (debris) generated by multi-pulse
femtosecond laser ablation, (2) transformation of laser pulses into light filaments, and (3) low-fluence finishing.
Received: 15 November 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +49-511/2788-100, E-mail: ch@lzh.de 相似文献
74.
P.E. Dyer S.M. Maswadi C.D. Walton 《Applied Physics A: Materials Science & Processing》2003,76(5):817-822
We report an investigation of the ablation of NaCl crystals at the 157-nm wavelength of the F2 laser where there is very strong excitonic absorption. Probe-beam deflection and etch-rate measurements show that the interaction
is characterised by a low ablation threshold (∼80 mJ cm-2) and a capability for controllable material removal at the nanometer level. Scanning electron microscopy of the exposed surfaces
show this to be microscopically smooth but with fine cracks present. It is demonstrated that micron-scale features can be
formed in NaCl using 157-nm laser ablation, a result attributed to the strongly localised optical and thermal nature of the
interaction. The results are discussed within the framework of a thermal vaporisation model.
Received: 29 May 2002 / Accepted: 17 July 2002 / Published online: 4 November 2002
RID="*"
ID="*"Corresponding author. Fax: +44-1482/465606, E-mail: p.e.dyer@hull.ac.uk 相似文献
75.
We investigate the plasmon resonances for silver nanowires with a non-regular cross section. To study the relationship between
the cross section and the spectrum of the plasmon resonances, we consider cross sections evolving from a rectangular shape
to a triangular one. In particular, we study the influence of the sharpness of a corner on the near-field enhancement at the
vicinity of a particle and discuss its implications for surface-enhanced Raman scattering. We also investigate the influence
of the absorption on the plasmon-resonance spectrum and on the near-field enhancement.
Received: 15 August 2001 / Published online: 10 October 2001 相似文献
76.
E.G. Gamaly A.V. Rode A. Perrone A. Zocco 《Applied Physics A: Materials Science & Processing》2001,73(2):143-149
We present two sets of experimental results on the ablation-rate decrease with increase of the number of consecutive laser
pulses hitting the same spot on the target surface. We have studied laser ablation of a carbon target with nanosecond pulses
in two different interaction regimes: one with a XeCl laser (λ=308 nm) and the other with a Nd:YAG laser (λ=1064 nm), in both
cases at the intensity ∼5×108 W/cm2 Two different mechanisms were found to be responsible for the ablation-rate decrease; they are directly related to the two
different laser–matter interaction regimes. The UV-laser interaction is in the regime of transparent vapour (surface absorption).
The increase of the neutral vapour density in the crater produced by the preceding laser pulses is the main reason for the
decrease of ablation rate. With the IR laser each single laser pulse interacts with a partially ionised plume. With increase
of the number of pulses hitting the same spot on the target surface, the laser–matter interaction regime gradually changes
from the near-surface absorption to the volume absorption, resulting in the decrease in absorption in the target and thus
in the decrease in the ablation rate. The change in the evaporation rate was considered for both vacuum and reactive-gas environments.
Received: 21 February 2001 / Accepted: 26 February 2001 / Published online: 23 May 2001 相似文献
77.
In order to understand the physical mechanism, time-resolved dynamics of 355 nm nanosecond laser induced entrance and exit surface damage on fused silica was investigated by using shadow graphic technique. The results show that the damage mechanism is different between the entrance and exit surface during nanosecond laser interaction with fused silica. The plasma and shock waves in air is relatively higher at the entrance surface. The entrance surface damage is reduced because plasma shielding limits energy deposition. Without plasma shielding, the exit surface damage is more serious for more laser energy deposition in material. And without the stress of plasma and shock waves, the material is ejected easily at rear surface. These are confirmed by damage micrograph at the entrance and exit surface. 相似文献
78.
Ultrashort pulsed laser ablation in vacuum of different targets was performed in order to investigate the possibility of producing nanoparticles with controlled size and shape. A systematic morphology characterization of deposited products was performed for nickel and silicon as a function of laser pulse intensity and wavelength, at a fixed pulse repetition rate. The nanoparticles were investigated by atomic force microscopy, and clear trends for their size and shape anisotropy were evidenced. The best conditions to obtain nanosized particles of oblate ellipsoidal shape, with the minor axis below 10 nm, were determined in the case of nickel targets. Our results show that ultrashort pulse laser deposition can be considered as an interesting technique for the tailoring of nanogranular films with the desired particles dimension and shape, according to the peculiar properties required in specific applications. Moreover, the preliminary features are very promising from the point of view of the production of magnetoresistive films with specific anisotropy. 相似文献
79.
A. Gold 《Zeitschrift für Physik B Condensed Matter》1994,94(4):395-399
We present an analytical model for the Coulomb interaction effects in quantum wires forming a nanochannel array. We study the elementary excitations (plasmons and electron-hole excitations) of electron arrays forming three-dimensional structures. The plasmon spectrum of boson arrays is also calculated. Our model applies to bulk material with one-dimensional conduction channels as realized in organic or polymer crystals and in nanochannel array glasses. 相似文献
80.
Wolfgang Häusler 《Zeitschrift für Physik B Condensed Matter》1995,99(1):551-560
The lowest excitations of a repulsively interacting few particle system are investigated within correlated “pocket state”
basis functions. For long range interaction and non-isotropic confining potentials the method becomes exact, in the limit
of large mean inter-particle distancesr
s. The multiplet structure of the many-electron energy levels is explained and the ratios δ between the lowest excitation energies,
which are related to the electron spin, are determined quantitatively using group theoretical means. The δ are independent
of the detailed form of the inter-particle repulsion and of sufficiently larger
s. The obtained δ-values are confirmed by available numerical data. The method is applied to 1D and 2D quantum dots. 相似文献