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1.
The multi-layers coupled-wave theory is extended to systematically investigate the pulse shaping and diffraction properties
of a system of multi-layers reflection volume holographic gratings (MRVHG) under ultrashort laser pulse (ULP) readout. The
combined effects that the grating parameters such as the number and thickness of layers and gaps between them and the pulse
duration of the input ULP have on the pulse shaping properties are considered. The pulse profiles of the diffracted and transmitted
beams, the diffraction bandwidth, and the total diffraction efficiency are presented. The calculated results we have derived
permit an optimal choice of grating parameters for the pulse shaping and process applications. 相似文献
2.
We report on an angularly tunable laserline notch filter from 760 to 785 nm with optical density of 5.7, 3 dB bandwidth of
9 cm−1 (0.55 nm) and greater than 80% transmission. The notch filter is a single element composed of six bonded slanted reflective
holographic gratings in glass. 相似文献
3.
The dependence of the maximal diffraction efficiency of a volume reflection hologram recorded in a cubic optically active
photorefractive piezocrystal on the crystal thickness is investigated. The theoretical analysis is fulfilled on the basis
of the coupled wave equations in a static grating approximation taking into account the linear electro-optic, inverse piezoelectric,
and photoelastic effects. The optimal cuts of the crystals with various thickness for which the maximal diffraction efficiency
of the reflection hologram can be attained are determined. It is shown that the optical activity of the crystal is responsible
for a variety of the optimal cuts corresponding to different crystal thicknesses. Effect of the crystal on the dependence
of the maximal diffraction efficiency of the reflection hologram on a crystal cut is discussed. 相似文献
4.
We investigate non-volatile holographic data storage in photorefractive lithium niobate crystals. Infrared picosecond laser
pulses are used to write holograms after sensitizing the crystal with blue light from a cw-laser. The dependence of the dynamic
range and the photoconductivity on the pulse intensities and the recording wavelength is investigated in detail. The results
can be explained by a two-center model if the mean intensity of the laser pulses is considered. We demonstrate that several
fixed holograms can be multiplexed by employing the wavelength multiplexing technique. 相似文献
5.
Holographic phase conjugation is analyzed as a method to create a photo-refractive lens with high numerical aperture. For
this purpose a sub-wavelength hole is drilled into a metal surface directly on top of an iron-doped lithium niobate crystal.
An interference pattern generated by the light coming from this point source and a plane reference wave is recorded. By using
the phase-conjugated reference wave for read-out, a light wave being focused onto the former point source is reconstructed.
In principle, a focusing system close to the theoretical diffraction limit could be implemented by this method. The performance
of this arrangement is mainly determined by properties of the lithium niobate crystal, especially the crystal symmetry. Experimentally,
the tight holographic focusing is demonstrated. The focus width of the reconstructed wave is shown to be below 1.2 μm, which
is our spatial resolution. The diffraction efficiency obtained, however, is just 3×10−5 compared to 3×10−2 in the plane-wave case. This can be explained by experimental reasons, the inhomogeneous light intensity and limitations
originating from the crystal symmetry. We estimate that the diffraction efficiency for phase conjugation through a sub-wavelength
hole can be improved by three to four orders of magnitude by addressing the above-mentioned issues. 相似文献
6.
In the Shallow Water’ 06 experiment, two L-shape arrays (ARRAY52 and ARRAY32) were deployed. The vertical line array (VLA)
components of both ARRAY52 and ARRAY32 were exactly perpendicular to the direction of sound propagation. The horizontal line
array (HLA) component of ARRAY52 was exactly perpendicular to the direction of sound propagation. The HLA component of ARRAY32
was exactly parallel to the direction of sound propagation. This configuration offered an opportunity to simultaneously analyze
the three dimensional (3-D) spatial coherences: vertical, transverse horizontal and longitudinal horizontal. When the source
and the receivers were below the thermocline, both the vertical and longitudinal horizontal coherence lengths in units of
wavelength increased with increasing range and frequency. When the source was within the thermocline, the transverse horizontal
coherence length in units of wavelength decreased with frequency and exhibited weak range dependence.
The text was submitted by the authors in English. 相似文献
7.
The empirical mode decomposition (EMD) method is used to process sequences of dynamic speckle patterns to segment the differential activity that presents a sample as a function of the spatial coordinates and time. The application of the method is illustrated by segmenting bruised regions in fruits. A discussion of the obtained results and a comparison with the use of the filter bank technique are also presented. 相似文献
8.
Yu-Chia Chang Larry A. Coldren 《Applied Physics A: Materials Science & Processing》2009,95(4):1033-1037
High-efficiency, high-speed, tapered-oxide-apertured vertical-cavity surface-emitting lasers (VCSELs) emitting at 980 nm have
been demonstrated. By carefully engineering the tapered oxide aperture, the mode volume can be greatly reduced without adding
much optical scattering loss for the device sizes of interest. Consequently, these devices can achieve higher bandwidth at
lower current and power dissipation. In addition, the parasitics are reduced by implementing deep oxidation layers and an
improved p-doping scheme in the top mirror. Our devices show modulation bandwidth exceeding 20 GHz, a record for 980 nm VCSELs. Moreover,
35 Gb/s operation has been achieved at only 10 mW power dissipation. This corresponds to a data-rate/power-dissipation ratio
of 3.5 Gbps/mW. Most importantly, our device structure is compatible with existing manufacturing processes and can be easily
manufactured in large volume making them attractive for optical interconnects. 相似文献
9.
Molecular imaging by Mid-IR laser ablation mass spectrometry 总被引:1,自引:0,他引:1
Akos Vertes Peter Nemes Bindesh Shrestha Alexis A. Barton Zhaoyang Chen Yue Li 《Applied Physics A: Materials Science & Processing》2008,93(4):885-891
Mid-IR laser ablation at atmospheric pressure (AP) produces a mixture of ions, neutrals, clusters, and particles with a size
distribution extending into the nanoparticle range. Using external electric fields the ions can be extracted and sampled by
a mass spectrometer. In AP infrared (IR) matrix-assisted laser desorption ionization (MALDI) experiments, the plume was shown
to contain an appreciable proportion of ionic components that reflected the composition of the ablated target and enabled
mass spectrometric analysis. The detected ion intensities rapidly declined with increasing distance of sampling from the ablated
surface to ∼4 mm. This was rationalized in terms of ion recombination and the stopping of the plume expansion by the background
gas. In laser ablation electrospray ionization (LAESI) experiments, the ablation plume was intercepted by an electrospray.
The neutral particles in the plume were ionized by the charged droplets in the spray and enabled the detection of large molecules
(up to 66 kDa). Maximum ion production in LAESI was observed at large (∼15 mm) spray axis to ablated surface distance indicating
a radically different ion formation mechanism compared to AP IR-MALDI. The feasibility of molecular imaging by both AP IR-MALDI
and LAESI was demonstrated on targets with mock patterns.
Presented at the 9-th International Conference on Laser Ablation, 2007 Tenerife, Canary Islands, Spain 相似文献
10.
O. I. Meshkov S. A. Glukhov V. F. Gurko A. D. Khilchenko V. A. Kiselev E. B. Levichev N. Yu. Muchnoi P. A. Piminov V. V. Smaluk A. N. Zhuravlev 《Physics of Particles and Nuclei Letters》2008,5(7):601-604
The experiments in measuring the dynamic aperture and beam energy spread of the VEPP-4M collider [1] are described. The optical
diagnostics of the accelerator were applied for these purposes.
The text was submitted by the authors in English. 相似文献
11.
We demonstrate that for a given pump source, there is an optimum pump threshold to achieve the maximum single-frequency output
power in singly resonant optical parametric oscillators. Therefore, cavity losses and parametric amplification have to be
adjusted. In particular, continuous-wave output powers of 1.5 W were achieved with a 2.5 cm lithium niobate crystal in comparison
with 0.5 W by a 5 cm long crystal within the same cavity design. This counter-intuitive result of weaker amplification leading
to larger powers can be explained using a model from L.B. Kreuzer (Proc. Joint Conf. Lasers and Opt.-Elect., p. 52, 1969). Kreuzer also states that single-mode operation is possible only up to pump powers which are 4.6 times the threshold value.
Additionally, implementing an outcoupling mirror to increase losses, single-frequency waves with powers of 3 W at 3.2 μm and 7 W at 1.5 μm could be generated simultaneously. 相似文献
12.
E. Ambite D. Balboa J. L. Plaza L. Arizmendi 《Applied physics. B, Lasers and optics》2009,95(3):447-452
We have investigated the properties of thermally fixed holograms in LiNbO3 crystals doped with the optical damage inhibitor Zn as well as the photorefractive Fe dopants. Time decays of fixed holograms
at different temperatures showed a single thermally activated process with an activation energy of ∼1.08 eV. We have also
studied the effect of an external electric field on the diffraction efficiency of these holograms. Results analysis has provided
a new method to determine the photovoltaic field of the samples as well as the effective concentration of photorefractive
traps. 相似文献
13.
The mode-hop behavior and the power characteristics of a laser diode with wavelength-selective optical feedback are experimentally
investigated. The feedback is provided by external volume holographic gratings, also called ‘Bragg mirrors’, at normal incidence.
We demonstrate that a Bragg mirror forces a laser diode to operate only within a narrow wavelength range, and that the emission
wavelength of the laser diode is stabilized against variations of the injection current. Moreover, we present periodic undulations
of the power characteristics of the laser, depending on the driving current. They can be qualitatively explained with a simple
model which takes into account that the threshold gain in the laser system strongly depends on the wavelength. 相似文献
14.
R. Proietti Zaccaria S. Shoji H.-B. Sun S. Kawata 《Applied physics. B, Lasers and optics》2008,93(1):251-256
A mathematical scheme capable of describing the features of the photolithographic multi-beam–multi-shot approach is introduced
here. We will show in detail how such a technique can reproduce any of the fourteen three-dimensional Bravais lattices. Furthermore,
we will mathematically show the independence of the lattice constant of the structure from the laser wavelength. Finally,
we will compare the four-beams–one-shot and the three-beams–three-shots techniques by means of simulations reproducing opal
and connected FCC-like lattices. 相似文献
15.
We demonstrate the existence of higher-order solitons occurring at an interface separating two one-dimensional (1D) Bessel
optical lattices with different orders or modulation depths in a defocusing medium. We show that, in contrast to homogeneous
waveguides where higher-order solitons are always unstable, the Bessel lattices with an interface support branches of higher-order
structures bifurcating from the corresponding linear modes. The profiles of solitons depend remarkably on the lattice parameters
and the stability can be enhanced by increasing the lattice depth and selecting higher-order lattices. We also reveal that
the interface model with defocusing saturable Kerr nonlinearity can support stable multi-peaked solitons. The uncovered phenomena
may open a new way for soliton control and manipulation. 相似文献
16.
Alexander Horn Ilja Mingareev Alexander Werth Martin Kachel Udo Brenk 《Applied Physics A: Materials Science & Processing》2008,93(1):165-169
Lead-free piezoelectric ceramics Bi0.5(Na1-x-yKxAgy)0.5TiO3 [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K+ and Ag+ on the electrical properties were examined. X-ray diffraction patterns indicate that K+ and Ag+ ions partially substitute for the Na+ ions in Bi0.5Na0.5TiO3 and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric
constant d33=189 pC/N, electromechanical coupling factor kp=35.0%, remanent polarization Pr=39.5 μC/cm2, and coercive field Ec=3.3 kV/mm, respectively. The curves of the dielectric constant εr and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase
decreases with increasing the K+ content for the compositions researched. The dependencies of kp and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature Td of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d33=134 pC/N, kp=32.5%) and strong ferroelectricity (Pr=39.5 μC/cm2, Ec=4.1 kV/mm) at room temperature, is above 160 °C.
PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy 相似文献
17.
A. Rodenberg S. Fechner F. Dimler D. J. Tannor T. Brixner 《Applied physics. B, Lasers and optics》2008,93(4):763-772
The characterization and interpretation of ultrashort laser pulses is most intuitive in the joint time–frequency domain, where
structures like multiple pulses become immediately apparent. For practical reasons, ultrafast femtosecond laser pulse shaping,
however, is commonly carried out in the frequency domain. Here we implement pulse shaping of optical fields defined in the
von Neumann representation, which is a joint time–frequency distribution with complex-valued Gaussian basis functions. We
discuss the feasibility as well as the principal limitations of this technique, show illustrative examples, and propose possible
applications in coherent control. 相似文献
18.
Mubasher Jamil M. Umar Farooq Muneer Ahmad Rashid 《The European Physical Journal C - Particles and Fields》2009,61(3):471-476
In this paper, the model of the holographic Chaplygin gas has been extended to two general cases: first the case of a modified
variable Chaplygin gas and second the case of the viscous generalized Chaplygin gas. The dynamics of the model is expressed
by the use of scalar fields and scalar potentials. 相似文献
19.
J. T. Dickinson 《Applied Physics A: Materials Science & Processing》2008,92(4):1025-1030
Below laser fluences where a plasma is formed (the so-called plasma or plume formation threshold) a number of fundamental
phenomena can occur where particles such as atomic and molecular ions, atoms and molecular neutrals, and electrons can be
emitted. An understanding of such processes is necessary to develop predictive models for material removal from laser irradiated
surfaces—at the foundation of laser etching, machining, and pulsed laser deposition. We have reported on a number of the mechanisms
for such emission processes. Here, due to space limitations, we present a summary of our studies on the formation of negative
alkali ions from single crystal KCl during exposure to pulsed 248-nm radiation at fluences well below the threshold for plasma
formation. Despite the high electron affinities of the corresponding halogen atoms, negative halogen ions were not detected.
Significantly, the positive and negative alkali ion distributions overlap strongly in time and space, consistent with K formation
by the sequential attachment of two electrons to K+. Negative alkali ions are also observed under comparable conditions from LiF, NaCl, and KBr. In each material, the strong
overlap between the positive and negative alkali ion distributions, and the lack of detected negative halogen ions, suggest
that negative ion formation involves a similar mechanism. 相似文献
20.
M. Vainio J. Peltola S. Persijn F. J. M. Harren L. Halonen 《Applied physics. B, Lasers and optics》2009,94(3):411-427
Stability and tuning characteristics of continuous-wave optical parametric oscillators (CW OPOs) are affected by various thermal
effects arising from optical absorption in nonlinear crystals. In this paper, we present an experimental study of such effects
in a singly resonant CW OPO. The OPO operates in the 3-μm mid-infrared region and it is based on a MgO-doped periodically
poled lithium niobate crystal. We focus our study on two thermally induced phenomena that have been recently reported to exist
in singly resonant CW OPOs: optical bi-stability and thermal self-locking. Thermal self-locking effect, which is known to
alter the stability and tuning properties of doubly and triply resonant CW OPOs, is shown to be also of importance in singly
resonant OPOs. We report the stability and tuning characteristics of a thermally loaded OPO and discuss a simple temperature-tuning
method that can be used to scan the OPO idler frequency continuously over several THz. 相似文献