共查询到20条相似文献,搜索用时 15 毫秒
1.
Far-infrared signature of animal tissues characterized by terahertz time-domain spectroscopy 总被引:1,自引:0,他引:1
We present terahertz time-domain spectroscopy characterization of various animal tissues obtained from pork and rats. As the sensitivity of terahertz radiation to polar molecules of water is very high, biological tissues with high level of hydration show strong absorption at terahertz frequencies. The experimental data indicate that skin, fat and lean pork tissues have different frequency-dependent response to terahertz radiation due to the variation in water content. The same type tissue from different animals, however, is observed to show very similar water absorption. 相似文献
2.
M. Hentschel S. Uemura Z. Cheng S. Sartania G. Tempea C. Spielmann F. Krausz 《Applied physics. B, Lasers and optics》1999,68(1):145-148
Received: 9 June 1998/Revised version: 4 November 1998 相似文献
3.
M. Nisoli G. Sansone S. Stagira C. Vozzi S. De Silvestri O. Svelto 《Applied physics. B, Lasers and optics》2002,75(6-7):601-604
A novel spectral broadening technique, based on hollow-fiber cascading, is reported, which allows the generation of a supercontinuum
extending to a bandwidth exceeding 510 THz with excellent spatial beam quality. High-peak-power, sub-7-fs light pulses tunable
from the visible to the near infrared have been generated by compression of portions of the supercontinuum, employing different
sets of chirped mirrors.
Received: 11 July 2002 / Revised version: 3 September 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +39-02/2399-6126, E-mail: mauro.nisoli@fisi.polimi.it 相似文献
4.
A.A. Babin D.V. Kartashov A.M. Kiselev V.V. Lozhkarev A.N. Stepanov A.M. Sergeev 《Applied physics. B, Lasers and optics》2002,75(4-5):509-514
. We report on the experimental and theoretical study of spectrum transformation and frequency blue-shift of femtosecond laser
pulses with intensities up to 2×1016 W/cm2, propagating in glass capillary tubes under gas ionization. Monomode optical guiding with 45% transmission efficiency is
demonstrated in a 100-μm-diameter, 20-cm length capillary. A broadening of the initial spectrum as much as several initial
spectrum widths is achieved. Besides the broadening, the mean frequency of the output radiation in the spectrum experiences
a blue-shift of up to several initial spectrum widths, caused by the non-stationary, non-linear process of gas ionization.
Our numerical simulations, in the form of a simple one-dimensional model for the propagation of intense laser pulses in gas-filled
capillaries, are in good qualitative agreement with the experimental results. These simulations show the possibility of significant
compression of an output pulse in a simple compression scheme (e.g. a piece of silica glass with normal dispersion), which
is very important for obtaining laser pulses with few optical cycles at the millijoule energy level.
Received: 25 September 2001 / Revised version: 6 December 2001 / Published online: 25 September 2002
RID="*"
ID="*"Corresponding author. Fax: +7-8312/363-792, E-mail: dekart@ufp.appl.sci-nnov.ru 相似文献
5.
O. Steinkellner M. Wittmann G. Korn I.V. Hertel 《Applied physics. B, Lasers and optics》2001,73(3):279-281
We use sub-10-fs pulses at 400 nm and 15-fs pulses at 800 nm to ionize water molecules and their isotopomers HDO and D2O in a pump–probe scheme. Pulses are generated via spectral broadening of 25-fs pulses of a 1-kHz Ti:sapphire amplifier system
by self-phase modulation in a noble-gas-filled hollow waveguide and subsequent compression using chirped mirrors. At this
time scale vibronic excitation of the first bending mode of water in the electronic ground state by impulsive Raman scattering
is possible (e.g. the fundamental bending mode of H2O: tvib=20 fs). The effect of this pre-excitation on the ionization rate is shown.
Received: 14 May 2001 / Revised version: 24 August 2001 / Published online: 19 September 2001 相似文献
6.
Albert O. Roger S. Glinec Y. Loulergue J.C. Etchepare J. Boulmer-Leborgne C. Perrière J. Millon E. 《Applied Physics A: Materials Science & Processing》2003,76(3):319-323
We have studied the plasma induced at the surface of a titanium target following irradiation with femtosecond and nanosecond
laser pulses. Time-resolved imaging and spectroscopic measurements allowed us to evidence some features specific to the femtosecond-laser-induced
plasma. In this ultrashort interaction regime, we could discriminate between three different velocity populations in the plasma
expansion. Coulomb explosion firstly creates highly energetic Ti+ ions, which are followed by atomic neutral titanium and lastly by nanoscale titanium oxide clusters.
Received: 28 September 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +33-1/6931-9996, E-mail: albert@ensta.fr 相似文献
7.
C.O. Weiss M. Vaupel K. Staliunas G. Slekys V.B. Taranenko 《Applied physics. B, Lasers and optics》1999,68(2):151-168
We give in this article the mathematical background for pattern formation in nonlinear active resonators, elucidating the
relation of optics with other fields of physics, and demonstrate experimentally the existence, properties, and dynamics of:
(i) vortices in lasers,
(ii) bright spatial solitons in lasers with saturable absorber, and
(iii) spatial solitons in degenerate parametric mixing.
All these structures are by definition bistable so that they are potentially useful for parallel optical information processing.
Received: 8 June 1998 相似文献
8.
M. Lorenc M. Ziolek R. Naskrecki J. Karolczak J. Kubicki A. Maciejewski 《Applied physics. B, Lasers and optics》2002,74(1):19-27
The paper discusses three different artifacts related to two-photon absorption (TPA), stimulated Raman amplification (SRA)
and cross-phase modulation (XPM), all intrinsic to transient absorption measurements with femtosecond time resolution. Certain
properties of these signals are analysed and shown to superimpose onto measured transient absorption spectra. Ways of reducing
the influence of the artifacts discussed are suggested. A simple correcting procedure based on the linear intensity dependence
of the artifacts discussed is proposed.
Received: 29 May 2001 / Final version: 15 October 2001 / Published online: 29 November 2001 相似文献
9.
It was shown recently that an ensemble of solitons can be created in a driven optical fiber resonator. The ensemble can exist
in either an ordered or a disordered state; these have been referred to as soliton solid or gas (fluid), respectively. We
demonstrate through numerical simulation that the transition from one state to the other or vice versa, and further manipulation
of the ensemble, can be effected through the insertion of spectral filters.
Received: 7 July 2000 / Revised version: 1 September 2000 / Published online: 30 November 2000 相似文献
10.
A novel-high energy pulse compression system: generation of multigigawatt sub-5-fs pulses 总被引:2,自引:0,他引:2
M. Nisoli S. Stagira S. De Silvestri O. Svelto S. Sartania Z. Cheng M. Lenzner C. Spielmann F. Krausz 《Applied physics. B, Lasers and optics》1997,65(2):189-196
Received: 28 February 1997 / Revised version: 2 May 1997 相似文献
11.
We have developed a novel interferometric autocorrelator composed of only reflective elements, which functions as a beam splitter
and an optical delay line. Analytical expressions are derived to give second-order autocorrelation functions and deconvolution
factors for various conditions. The measurement of femtosecond laser pulses by interferometric autocorrelation is demonstrated
in the visible region. The results are compared with those by calculation.
Received: 9 December 2002
Revised version: 18 February 2003 / Published online: 5 May 2003
RID="*"
ID="*"Present address: Department of Physics, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1207, Japan
RID="**"
ID="**"Corresponding author. Fax: +81-48/462-4682, E-mail: asuda@postman.riken.go.jp 相似文献
12.
We demonstrate an optical limiter for ultra-short (∼100-fs) laser pulses. The device has a dynamic range (= damage energy/onset-of-limiting
energy) of more than 10000 and an onset-of-limiting energy of only ∼10 nJ. The output-pulse energy is kept below 1.3 μJ. The
limiting mechanism is based on two-photon absorption and refractive nonlinearities in a 20-mm piece of ZnSe. We discuss the
importance of the different nonlinearities, damage issues, and guidelines for the construction of the device.
Received: 20 December 2001 / Revised version: 25 March 2002 / Published online: 8 May 2002 相似文献
13.
B. Köhler U. Bäder A. Nebel J.-P. Meyn R. Wallenstein 《Applied physics. B, Lasers and optics》2002,75(1):31-34
We report on an injection-seeded 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator (OPG) based on a 55 mm
long crystal of periodically poled lithium niobate (PPLN) with a quasi-phase-matching (QPM) grating period of 29.75 μm. The
OPG is excited by a continuously diode pumped mode-locked picosecond Nd:YVO4 oscillator-amplifier system. The laser system generates 7 ps pulses with a repetition rate of 82.3 MHz and an average power
of 24 W. Without injection-seeding the total average output power of the OPG is 8.9 W, which corresponds to an internal conversion
efficiency of 50%. The wavelengths of the signal and idler waves were tuned in the range 1.57–1.64 μm and 3.03–3.3 μm, respectively,
by changing the crystal temperature from 150 °C to 250 °C. Injection seeding of the OPG at 1.58 μm with 4 mW of single frequency
continuous-wave radiation of a distributed-feedback (DFB) diode laser increases the OPG output to 9.5 W (53% conversion efficiency).
The injection seeding increases the pulse duration and reduces the spectral bandwidth. When pumped by 10 W of 1.06 μm laser
radiation, the duration of the signal pulses increased from 3.6 ps to 5.5 ps while the spectral bandwidth is reduced from
4.5 nm to 0.85 nm. Seeding thus improved the time-bandwidth product from 1.98 to a value of 0.56, much closer to the Fourier
limit.
Received: 29 April 2002 / Published online: 8 August 2002 相似文献
14.
We demonstrate a novel traveling-wave type optical parametric generator based on 1.25 μm pumping of AgGaS2 that produces tunable, high-power and almost transform-limited 200-fs pulses in the mid-infrared up to 8 μm.
Received: 24 January 2000 / Revised version: 1 March 2000 / Published online: 5 April 2000 相似文献
15.
Visible femtosecond (fs) laser pulses have been obtained in a dye solution with a very simple traveling wave collinear configuration.
A femtosecond Ti:sapphire laser (790 nm) pumps the dye solution by two-photon absorption and simultaneously generates supercontinuum,
which seeds a light-amplification mechanism. Cross-correlation frequency-resolved optical gating measurements reveal a chirped
structure in the dye pulse. The shortest pulse duration achieved is 170 fs and the overall energy efficiency of the process
is typically 25%.
Received: 22 March 2001 / Revised version: 4 July 2001 / Published online: 19 September 2001 相似文献
16.
S. Tzortzakis G. Méchain G. Patalano M. Franco B. Prade A. Mysyrowicz 《Applied physics. B, Lasers and optics》2003,76(5):609-612
We report the first observation of the attachment of two single plasma filaments created collinearly in the atmosphere by
IR femtosecond laser pulses. The linked filamentary structure is electrically conductive and emits sub-THz radiation over
its entire length. Concatenation is achieved only for a specific time ordering between the two initial laser pulses. The pulse
producing the filament closer to the laser source must be retarded with respect to the other pulse. This special time ordering
is attributed to the acceleration of light in a self-guided pulse.
Received: 4 March 2003 / Published online: 14 May 2003
RID="*"
ID="*"Corresponding author. Fax: +33-1/6931-9996, E-mail: stzortz@ensta.fr 相似文献
17.
Ultra-fast spectroscopy and extreme nonlinear optics by few-optical-cycle laser pulses 总被引:3,自引:0,他引:3
G. Cerullo G. Lanzani M. Nisoli E. Priori S. Stagira M. Zavelani-Rossi O. Svelto L. Poletto P. Villoresi C. Altucci C. de Lisio 《Applied physics. B, Lasers and optics》2000,71(6):779-786
Many fundamental processes of radiation–matter interaction, which take place on the ultra-short time scale, can now be directly
investigated by using few-optical-cycles light pulses with duration <10 fs. We discuss two techniques for generating such
pulses: broad-band parametric amplification, which allows the generation of pulses in the visible range suitable for spectroscopy,
and compression of high-energy light pulses in a hollow fiber. As an example of application in time-resolved spectroscopy
we report results of pump–probe experiments in a prototypical conjugated molecule, namely sexithiophene. The new laser sources,
due to their characteristics of peak power and coherence, also allow the exploration of new fields of experimental physics,
such as extreme nonlinear optics. We focus on high-order harmonics, showing that a high-energy bunch of photons, up to the
X-ray-energy region, with coherence typical of laser radiation and time duration comparable to or shorter than the exciting
pulses, can be generated.
Received: 31 July 2000 / Revised version: 19 September 2000 / Published online: 8 November 2000 相似文献
18.
S. Ito H. Nagaoka T. Miura K. Kobayashi A. Endo K. Torizuka 《Applied physics. B, Lasers and optics》2002,74(4-5):343-347
We have measured detailed thermal lensing in a power amplifier of a terawatt Ti:sapphire laser operating at 50 Hz. The thermal
lensing in the amplifier was evaluated by measuring the optical path difference (OPD) using a Shack–Hartmann-type wavefront
sensor. It was found that the radial dependence of the OPD was almost quadratic in the pumping region, despite inhomogeneous
pumping. Therefore, a simple spherical lens or convex mirror effectively compensates for the thermal lens in our amplifier.
We found that the thermal lens profile was temporally stable, and did not degrade the pointing stability of the amplified
laser pulses. We also found that the time constant of the thermal distortion in our power amplifier was approximately 0.5 s.
Received: 3 September 2001 / Revised version: 23 January 2002 / Published online: 14 March 2002 相似文献
19.
The generation of programmable complex femtosecond pulses in the mid infrared (3–10 μm) with high precision is reported. Designed
pulse shapes in the near infrared (1–1.6 μm) are transferred to the mid infrared via difference-frequency mixing with a second
infrared pulse spectrally narrowed in a zero-dispersion compressor. In particular, pulse sequences with variable relative
phases have been obtained. The control of the pulse properties is achieved purely electronically, allowing for implementation
into a feedback loop.
Received: 12 December 2003 / Published online: 3 April 2003
RID="*"
ID="*"Corresponding author. Fax: +49-89/32905-200, E-mail: mcm@mpq.mpg.de 相似文献
20.
We report on an optical parametric amplifier (OPA) based on two potassium titanyl phosphate (KTP) crystals in a walk-off compensating
geometry. An Nd:YLF regenerative amplifier at a 1-kHz repetition rate serves as the pump source. The seed beam is delivered
by a synchronously pumped frequency-stabilized optical parametric oscillator (OPO) based on periodically poled lithium niobate
(PPLN). At pump intensities of about 7 GW/cm2 large amplification factors of more than 104 were achieved, resulting in pulse energies of more than 450 μJ and 350 μJ for the signal and idler pulses, respectively,
at a 1-kHz repetition rate. In the saturation regime the time–bandwidth product increases from two to three times the Fourier
limit, with a pulse duration of 105 ps and a bandwidth of 12.7 GHz at the highest intensities employed.
Received: 2 November 2001 / Published online: 14 March 2002 相似文献