共查询到20条相似文献,搜索用时 15 毫秒
1.
AFM, a tool for single-molecule experiments 总被引:2,自引:0,他引:2
M. Ludwig M. Rief L. Schmidt H. Li F. Oesterhelt M. Gautel H.E. Gaub 《Applied Physics A: Materials Science & Processing》1999,68(2):173-176
Received: 27 March 1998 相似文献
2.
T. Hornung R. Meier D. Zeidler K.-L. Kompa D. Proch M. Motzkus 《Applied physics. B, Lasers and optics》2000,71(3):277-284
This paper reports two pump–probe experiments in sodium where dynamically tailored ultrashort pulses from a Ti:Sapphire-pumped
optical parametric amplifier were employed. The first study focuses on the one-photon Na(3s→3p) transition to derive sensitive
criteria which judge the performance of a frequency-domain pulse shaper using a spatial light modulator. On the basis of the
interpretation, follow-up experiments are suggested to test their cogency. The second experiment uses coherent quantum control
by placing an appropriate phase distribution on the incident beam to enhance or cancel the transition probability in the nonresonant
two-photon process Na(3s→→5s). Ignorant of the “ideal” phase function, an evolutionary algorithm which uses a feedback derived
from the experiment performs the optimization and produces the desired bright or dark pulses within a few minutes. Attention
is given to the role of resonant 3s→3p transitions excited by the spectral wings of the pump pulse. Different parametrizations
of the phase distribution have been examined. Two of these produced solutions which had not previously been predicted by theory
still meet the objective of the experiment. The study represents the first successful application of a feedback-organized
self-learning algorithm to the design of dark pulses.
Received: 3 November 1999 / Published online: 5 July 2000 相似文献
3.
Y.-L. Pan R.G. Pinnick S.C. Hill S. Niles S. Holler J.R. Bottiger J.-P. Wolf R.K. Chang 《Applied physics. B, Lasers and optics》2001,72(4):449-454
An unexpected blue-fluorescence band (around 420 nm) from both micrometer-sized dried particles and aqueous droplets of riboflavin
[7,8-dimethyl-10-(D-1′-ribityl)-isoalloxazine] is observed when the microparticles are irradiated with a pulsed UV (355- or 351-nm) laser. The intensity
of the band increases quadratically with input laser energy density (fluence) and is attributable to a one-photon-excited
fluorescence of lumichrome (7,8-dimethyl-alloxazine) that is produced by photo-degradation of riboflavin. The well-known greenish-yellow
fluorescence band (at 560 nm for dried particles and 535 nm for aqueous droplets) from riboflavin increases sublinearly with
UV-laser fluence. With a laser input fluence above 5 J/cm2 the riboflavin fluorescence decays earlier and the lumichrome fluorescence reaches a maximum later than the peak of the input
laser pulse. The temporal dynamics of the 420- and 535-nm fluorescence peaks are consistent with a rate-equation simulation
of photon-induced conversion of riboflavin to lumichrome and the subsequent fluorescence of lumichrome.
Received: 28 September 2000 / Revised version: 11 December 2000 / Published online: 21 February 2001 相似文献
4.
5.
T.B. Settersten A. Dreizler B.D. Patterson P.E. Schrader R.L. Farrow 《Applied physics. B, Lasers and optics》2003,76(4):479-482
This study reports on photochemical interferences affecting atomic oxygen detection using two-photon laser-induced fluorescence
at 226 nm. In contrast to previous studies in which molecular oxygen was proven to be the relevant photochemical precursor
molecule in a hydrogen-fueled flame, the present investigations were carried out in a laminar diffusion flame of methane and
air. The most significant interferences were found at the fuel side of the flame in the absence of molecular oxygen, and vibrationally
excited carbon dioxide was identified as the most probable precursor molecule for the photochemical production of oxygen atoms.
Received: 11 December 2002 / Revised version: 10 March 2003 / Published online: 16 April 2003
RID="*"
ID="*"Corresponding author. Fax: +1-925/294-2595, E-mail: tbsette@sandia.gov 相似文献
6.
M. Masuda K. Sugioka Y. Cheng N. Aoki M. Kawachi K. Shihoyama K. Toyoda H. Helvajian K. Midorikawa 《Applied Physics A: Materials Science & Processing》2003,76(5):857-860
We show that a femtosecond laser enables us to produce true three-dimensional (3-D) microstructures embedded in a photosensitive
glass, which has superior properties of transparency, hardness and chemical and thermal resistances. The photosensitivity
arises from the cerium in the glass. After exposure to a focused laser beam, latent images are written. Modified regions are
developed by a post-baking process and then preferentially etched away in a 10% dilute solution of hydrofluoric acid at room
temperature. We have measured the critical dose for modification of the photosensitive glass, and fabricated 3-D microstructures
with microcells and hollow microchannels embedded in the glass based on the critical dose.
Received: 12 August 2002 / Accepted: 13 August 2002 / Published online: 4 December 2002
RID="*"
ID="*"Corresponding author. Fax: +81-48/468-4682, E-mail: mmasudaw@postman.riken.go.jp 相似文献
7.
G.L. Duveneck M.A. Bopp M. Ehrat M. Haiml U. Keller M.A. Bader G. Marowsky S. Soria 《Applied physics. B, Lasers and optics》2001,73(8):869-871
Two-photon excitation (TPE) of fluorescence is a powerful tool for separating a faintly emitted fluorescence signal from background
excitation noise. Until now TPE has only been accomplished for very small excitation areas of a few square micrometre dimensions
since they are readily available in the focal zone of high-power lasers. In this paper we demonstrate, to our knowledge for
the first time, two-photon excited fluorescence with planar thin-film waveguide structures of macroscopic excitation areas
of the order of square millimetres to square centimetres.
Based upon our results, it can be envisaged that the new combination of planar waveguide technology with TPE will become a
powerful tool for macroscopic surface-interaction studies. It can also open the way for further improving the sensitivity
of biosensing platforms like genomic and proteomic microarrays based upon planar waveguides.
Received: 7 November 2001 / Published online: 23 November 2001 相似文献
8.
We perform Monte Carlo simulations of an existing electrophoretic microchannel device used for the size separation of large
DNA fragments. This device is normally operated with a constant (dc) driving field. In contrast, we consider the case of a
varying (ac) driving field, in the zero-frequency limit. We find that a time-asymmetric pulse can yield interesting migration
regimes, in particular bidirectional transport for different molecular sizes. We also study a spatially asymmetric version
of the device and show that it can rectify unbiased but non-equilibrium molecular motion, in agreement with previous predictions
for entropic ratchets. Finally, at finite frequency we uncover a resonance for the molecular velocity in the channel which
could lead to improved performance.
Received: 16 November 2001 / Accepted: 11 February 2002 / Published online: 22 April 2002 相似文献
9.
Electromagnetic interaction of fluorophores with designed two-dimensional silver nanoparticle arrays 总被引:1,自引:0,他引:1
H. Ditlbacher N. Felidj J.R. Krenn B. Lamprecht A. Leitner F.R. Aussenegg 《Applied physics. B, Lasers and optics》2001,73(4):373-377
We study the fluorescence enhancement of dye molecules adsorbed on regular two-dimensional arrays of designed silver nanoparticles.
The silver particles show two orthogonal optical resonances at different wavelengths because of their elongated shape. The
short-wavelength resonance was designed to fit to the absorption maximum of the fluorophore. When the excitation light drives
the short-wavelength resonance, the measured fluorescence intensity is strongly enhanced compared to that for the orthogonal
particle orientation. This shows directly a strong electromagnetic coupling between the nanoparticles and the fluorophore.
Additionally enhanced photochemical bleaching is observed due to the interaction of fluorophores with the particles. Using
a rate model describing the fluorescence enhancement and the bleaching enhancement, an average value for the particle-induced
increase in the radiative fluorescence rate is obtained, together with a lower limit for the averaged particle-induced field
intensity enhancement factor.
Received: 3 July 2001 / Revised version: 3 September 2001 / Published online: 15 October 2001 相似文献
10.
T. Lippert M. Hauer C.R. Phipps A. Wokaun 《Applied Physics A: Materials Science & Processing》2003,77(2):259-264
The ablation characteristics of various polymers were studied at low and high fluences for an irradiation wavelength of 308 nm.
The polymers can be divided into three groups, i.e. polymers containing triazene groups, designed ester groups, and reference
polymers, such as polyimide. The polymers containing the photochemically most active group (triazene) exhibit the lowest thresholds
of ablation (as low as 25 mJ cm-2) and the highest etch rates (e.g. 250 nm/pulse at 100 mJ cm-2), followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients have
a clear influence on the ablation characteristics. The different behavior of polyimide might be explained by a pronounced
thermal part in the ablation mechanism. The laser-induced decomposition of the designed polymers was studied by nanosecond
interferometry and shadowgraphy. The etching of the triazene polymer starts and ends with the laser pulse, indicating photochemical
ablation. Shadowgraphy reveals mainly gaseous products and a pronounced shockwave in air. The designed polymers were tested
for an application as the polymer fuel in laser plasma thrusters.
Received: 21 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +41-56/3104-412, E-mail: thomas.lippert@psi.ch 相似文献
11.
Ablation of organic polymers is described on the basis of photothermal bond breaking within the bulk material. Here, we assume
a first-order chemical reaction, which can be described by an Arrhenius law. Ablation starts when the density of broken bonds
at the surface reaches a certain critical value.
In order to understand the ablation behavior near the threshold fluence, φth, non-stationary regimes must be considered. The present treatment reveals several qualitative differences with respect to models that treat
ablation as a surface process: (i) Ablation starts sharply with a front velocity that has its maximum value just after the onset. (ii) The transition
to the quasi-stationary ablation regime is faster. (iii) Near threshold, the ablated depth h has a square-root dependence
on laser fluence, i.e., h∝(φ-φth)1/2. The ablation velocity is very high even near φth. (iv) With φ≈φth ablation starts well after the laser pulse. (v) The depletion of species is responsible for the Arrhenius tail observed with
fluences φ≤φth. (vi) Residual modification of material has maximum near the threshold. (vii) Stationary regimes of ablation demonstrate change of effective activation energy with laser intensity.
The model calculations are applied to Polyimide (KaptonTM H). Here, differences in single-pulse ablated depth determined from mass loss and profilometry should be about 10 nm.
Received: 16 February 1999 / Accepted: 18 February 1999 / Published online: 28 April 1999 相似文献
12.
Photo-bleaching phenomena occurring in chlorophyll-a were analysed by irradiation with UV and visible-spectrum sources. A
mathematical formalism was developed to quantify the optical spatio-temporal properties of the irradiated solutions. We also
measured the spatio-temporal changes of the optical response in photo-excited solutions. An empirical expression for the reaction
rate was obtained and the model used to quantify and understand the experimental bleaching results.
Received: 3 July 2001 / Revised version: 19 November 2001 / Published online: 7 February 2002 相似文献
13.
H. Tributsch 《Applied Physics A: Materials Science & Processing》2001,73(3):305-316
Based on the experimental observations that the three-phase nano-TiO2/F:SnO2/I-/I-
3 electrolyte front contact has to have pronounced rectifying properties (reverse reaction with electrolyte suppressed) for
efficient operation of the dye-sensitization solar cell and plays an active part in the generation of photoelectrochemical
energy, an analytical formula is derived which allows the understanding of the relevance and involvement of a variety of kinetic
and cell parameters. Essentially, the TiO2 layer is treated as a photocathode, donating electrons to a kinetically controlled front contact, with the counter-charges
being transported by the electrolyte within the pores. The formula was expanded to include photochemical kinetics of the sensitizer,
for which photodegradation properties were also calculated. The branching ratio, the ratio of regeneration-rate constant of
the sensitizer and of product-formation rate, turned out to be critical for long-term stability. It may have to be improved
by one order of magnitude for efficient cells to reach a lifetime of 20 years.
The degree of rectifying character of the nano-TiO2/F:SnO2/I-/I-
3 electrolyte interface (electric-field-dependent charge transfer to the front contact versus recombination-rate constant with
I3
- distinguishes between a low-efficiency (‘dynamic’) Galvani-type solar cell (efficiency determined by photoinduced chemical
potential gradients, no rectifying contact) and a more highly efficient ‘junction-type’ solar cell (separation and collection
of charges additionally assisted by junction potential). Several controversial subjects are addressed. The key challenges
for the improvement of such cells are discussed, especially with respect to photodegradation and to solid-state devices.
Received: 18 September 2000 / Accepted: 17 January 2001 / Published online: 20 June 2001 相似文献
14.
N. D. Lai W. L. Wang J. H. Lin C. C. Hsu 《Applied physics. B, Lasers and optics》2005,80(4-5):569-572
Optical manipulation of third harmonic (TH) generation in diarylethene-polymethylmethacrylate (DE-PMMA) polymer thin films is obtained by either one- or two-photon excitation. TH intensity generated from a DE-PMMA polymer thin film decreases, when it is pumped by either 325 nm or 442 nm laser irradiation, which changes the molecular structure of DE molecules from an open-form (A form) to a closed-form (B form). TH intensity recovers to its original intensity level when all B form DE molecules return to an A form after being induced by either 532 nm or 1064 nm laser irradiation. The experimental results reveal that the second-order hyperpolarizability () of the A form molecules may be larger than that of the B form molecules. Moreover, TH output efficiency is independent of the angle between the pump and probe polarization directions. This result is attributed to the two-dimensional structure of DE molecules.This revised version was published online in March 2005. In the previous version, the published online date was missing 相似文献
15.
Joseph R. Lakowicz Borys Kierdaszuk Ignacy Gryczynski Henryk Malak 《Journal of fluorescence》1996,6(1):51-59
We examined the steady-state and time-resolved emission of liver alcohol dehydrogenase resulting from one-photon and two-photon excitation. Previous studies with one-photon excitation revealed that the two nonidentical tryptophan residues display different emission spectra and decay times. The use of two-photon excitation resulted in similar emission spectra, multiexponential intensity decays, time-resolved emission spectra, and anisotropy decays as was observed for one-photon excitation. These results suggest that both nonidentical tryptophan residues are excited to a similar extent for one- and two-photon excitation. However, the limiting anisotropy (r
0) with two-photon excitation from 585 to 610 nm is below 0.1 and appears distinct from that observed previously forN-acetyl-l-tryptophanamide.Abbreviations LADH
liver alcohol dehydrogenase
- -NAD+
-nicotinamide adenine dinucleotide
- OPE
one-photon excitation
- OPIF
one-photon induced fluorescence
- TPE
two-photon excitation
- TCSPC
time-correlated single photon counting
- TPIF
two-photon induced fluorescence 相似文献
16.
Three-dimensional reversible laser micromachining of polymer materials based on two-photon photochromism is demonstrated.
Unamplified 60-fs, 0.5-nJ pulses of 790-nm Ti:sapphire laser radiation are used to induce a refractive-index change in a polymethyl
methacrylate (PMMA) sample doped with spiropyran molecules through a two-photon absorption process. Waveguides are written
in the bulk of spiropyran-doped PMMA samples by scanning these samples with respect to a tightly focused Ti:sapphire laser
beam. Laser-induced fluorescence is used for on-line monitoring of the laser-micromachining process. The structures written
in photochromic samples can be erased and reconfigured due to the reversibility of the photochromic effect.
Received: 23 April 2003 / Published online: 6 June 2003
RID="*"
ID="*"Corresponding author. Fax: +7-095/939-51-74, E-mail: zheltikov@top.phys.msu.su 相似文献
17.
Laser photolysis that releases characteristic photofragments, combined with laser-induced fluorescence (LIF) that subsequently
monitors them, facilitate detection of trace-vapor analytes in air. The feasibility of the technique is demonstrated for nitrocompounds
and organophosphonates detection. Using one-color and two-color lasers, respectively, the representative NO and PO photofragments
were tagged. Employment of longer wavelengths for photodissociation, and where possible also for LIF, than for fluorescence
collection, obstructs background fluorescence and in the former compounds also prevents interference of ambient ground state
NO.
Received: 1 February 2000 / Revised version: 27 April 2000 / Published online: 20 September 2000 相似文献
18.
C. Tomas E. Vinet J.-P. Girardeau-Montaut 《Applied Physics A: Materials Science & Processing》1999,68(3):315-320
Received: 1 October 1998 / Accepted: 30 October 1998 相似文献
19.
D. Bäuerle R. Denk J.D. Pedarnig K. Piglmayer J. Heitz G. Schrems 《Applied Physics A: Materials Science & Processing》2003,77(2):203-207
Laser-induced material processing is reviewed with special emphasis on recent achievements mainly obtained by the Linz group.
Among those are investigations using optical fiber tips for nanoscale photophysical etching, laser-induced surface patterning
using self-assembled microspheres, the pulsed-laser deposition of thin films of high-temperature superconductors and the modification
and cleaning of surfaces.
Received: 7 February 2003 / Accepted: 6 March 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +43-732/2468-9242, E-mail: dieter.baeuerle@jku.at 相似文献
20.
The temperature and excitation wavelength dependencies of 3-pentanone absorption and fluorescence were studied in support
of planar laser-induced fluorescence (PLIF) imaging of temperature and mixture fraction in flows of practical interest. The
temperature dependencies (300–875 K) of absorption and fluorescence were measured for gaseous 3-pentanoneat atmospheric pressure
in a nitrogen bath gas using 248, 266, and 308 nm excitation. The results indicate that the fluorescence signal per unit mole
fraction using 248 nm excitation is highly temperature-sensitive below 600 K, while the signal from 308 nm excitation is not
temperature sensitive below 500 K. For quantitative measurements over a broad range of temperatures, one must choose excitation
schemes carefully to balance the trade-off between measurement sensitivity and the amount of signal at the expected conditions.
As an example of such a choice and to show the capabilities of ketone PLIF techniques, we include temperature and mixture
fraction images of a 300–650 K heated air jet using near-simultaneous 308 and 266 nm excitation.
Received: 29 May 2002 / Revised version: 5 November 2002 / Published online: 26 February 2003
RID="*"
ID="*"Corresponding author. Fax: +1-650/723-1748, E-mail: jkoch@stanford.edu
RID="**"
ID="**"E-mail: hanson@me.stanford.edu 相似文献