共查询到20条相似文献,搜索用时 15 毫秒
1.
High resolution mode-selective excitation in the mixture of C6H6 (992 cm^-1) and C6D6 (945 cm^-1) is experimentally achieved by adaptive femtosecond pulse shaping based on the genetic algorithm (GA), and second harmonic generation frequency-resolved optical gating (SHG-FROG) is adopted to characterize the original and optimal laser pulses, and its mechanism is experimentally validated by tailoring the frequency components of the pump pulses at the Fourier plane. It is indicated that two-pulse coherent mode-selective excitation of the Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific molecular vibrational mode. The experimental results have attractive potential applications in the complicated molecular system. 相似文献
2.
We demonstrate that a broadband coherent anti-Stokes Raman scattering (CARS) spectrum generated with a typical two-pulse scheme contains two distinct, significant signals: '2-color' CARS, where the pump and probe are provided by a narrowband pulse and the continuum pulse constitutes the Stokes light, and '3-color' CARS, where the pump and Stokes are provided by two different frequency components in the continuum pulse and the narrowband pulse serves as the probe. The CARS spectra from the two different mechanisms show distinct characteristics in Raman shift range, laser power dependence, and chirping dependence. We discuss the potential for a 3-color CARS signal to cover the fingerprint region with reduced photodamage of live cells. Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. 相似文献
3.
We present a photonic crystal fiber (PCF)-based light source for generating tunable excitation pulses (pump and Stokes) that are applicable to coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The laser employed is an unamplified Ti:sapphire femtosecond laser oscillator. The CARS pump pulse is generated by spectral compression of a laser pulse in a PCF. The Stokes pulse is generated by redshifting a laser pulse in a PCF through the soliton self-frequency shift. This setup allows for probing up to 4000 cm(-1) with a spectral resolution of approximately 25 cm(-1). We characterize the stability and robustness of CARS microspectroscopy employing this light source. 相似文献
4.
The time evolution of the anti-Stokes signal produced from the non-linear interaction of a short Stokes pulse and two long
pump pulses that are nearly degenerate in frequency has been investigated. It is shown that this approach allows us to specify
the accuracy of CARS (coherent anti-Stokes Raman scattering) velocimetry and to extend the range of operation of the method.
In addition, an original optical scheme capable of delivering short visible pulses with good spatial and spectral properties
is reported. The optical bench has been used for the characterisation of a low-pressure laminar Mach-10 flow.
Received: 24 October 2001 / Revised version: 8 January 2002 / Published online: 14 March 2002 相似文献
5.
R. J. Heeman H. P. Godfried W. J. Witteman 《Applied physics. B, Lasers and optics》1995,60(5):479-484
High energy-conversion efficiencies in Stimulated Raman Scattering (SRS) are demonstrated both in experiments and by simulations for pump powers below SRS threshold. The scattering is induced by a short seed pulse at the Stokes frequency, the pulse width of which is much shorter than the pump pulse width and which is comparable with the medium's dephasing time. 相似文献
6.
We explore coherent control of stimulated Raman scattering in the nonimpulsive regime. Optical pulse shaping of the coherent pump field leads to control over the stimulated Raman output. A model of the control mechanism is investigated. 相似文献
7.
Pestov D Ariunbold GO Wang X Murawski RK Sautenkov VA Sokolov AV Scully MO 《Optics letters》2007,32(12):1725-1727
We present a comparative analysis of spontaneous and coherent Raman scattering on pyridine. The instantaneous excitation of the molecular coherence is done by a pair of ultrashort preparation pulses. Then, a long narrowband probe pulse is scattered off the molecular vibrations. The described hybrid technique allows for the single-shot acquisition of a background-free coherent Raman spectrum within the excitation band and its straightforward comparison with the spontaneous Raman measurements, performed in the same setup. We report a 10(5)-fold increase in the efficiency of the Raman scattering process due to the broadband pump-Stokes preparation. The coherence magnitude (approximately 0.5x10(-3)) is inferred experimentally, without a priori knowledge about the molecular structure. 相似文献
8.
A new Raman process can be used to realize efficient Raman frequency conversion by coherent feedback at low light intensity [Chen B, Zhang K, Bian C L, Qiu C, Yuan C H, Chen L Q, Ou Z Y, and Zhang W P 2013 Opt. Express 21, 10490].We present a theoretical model to describe this enhanced Raman process, termed as cascade correlation-enhanced Raman scattering, which is a Raman process injected by a seeded light field. It is correlated with the initially prepared atomic spin excitation and driven by the quasi-standing-wave pump fields, and the processes are repeated until the Stokes intensities are saturated. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics, and optical metrology due to its simplicity. 相似文献
9.
A. C. W. van Rhijn M. Jurna A. Jafarpour J. L. Herek H. L. Offerhaus 《Journal of Raman spectroscopy : JRS》2011,42(10):1859-1863
The identification of large molecules in complex environments requires probing of multiple vibrational resonances rather than a single resonance. Phase‐shaping the excitation pulses allows the coherent mixing of several resonances so that the presence of molecules can be inferred directly from the integrated output pulse energy. This avoids the need for the collection of spectra or multiple measurements. This article describes a particular implementation for coherent anti‐Stokes Raman scattering microscopy that uses a broadband pump and probe field in combination with a narrowband Stokes field. We numerically study the possibilities of optimizing selectivity, specificity, and sensitivity by precalculating pulse shapes using an evolutionary algorithm. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
Time-resolved femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of the nitrogen molecule is used for the measurement of temperature in atmospheric-pressure, near-adiabatic, hydrogen-air diffusion flames. The initial frequency-spread dephasing rate of the Raman coherence induced by the ultrafast (∼85 fs) Stokes and pump beams is used as a measure of gas-phase temperature. This initial frequency-spread dephasing rate of the Raman coherence is completely independent of collisions and depends only on the frequency spread of the Raman transitions at different temperatures. A simple theoretical model based on the assumption of impulsive excitation of Raman coherence is used to extract temperatures from time-resolved fs-CARS experimental signals. The extracted temperatures from fs-CARS signals are in excellent agreement with the theoretical temperatures calculated from an adiabatic equilibrium calculation. The estimated absolute accuracy and the precision of the measurement technique are found to be ±40 K and ±50 K, respectively, over the temperature range 1500-2500 K. 相似文献
11.
Simultaneous stimulated Raman scattering at the 992 cm–1 and the 3063 cm–1 line of benzene is observed by mode-locked ruby laser pulse excitation. The double line stimulated Raman scattering is initiated by self-focusing. The influence of small-scale self-focusing, self-phase modulation, and cross-phase modulation on the double line stimulated Raman scattering is discussed. At low pump pulse intensities, before the onset of small-scale self-focusing, the steady-state Raman gain factors of both Raman lines are determined by Raman energy conversion efficiency measurements. 相似文献
12.
To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering. 相似文献
13.
H. G. Häfele 《Applied Physics A: Materials Science & Processing》1974,5(2):97-108
The properties of the spin-flip Raman laser (SFR laser) which depend on stimulated Raman scattering from mobile conduction
electrons in InSb under an external magnetic field are presented. The essential parameters are derived from a macroscopic
treatment of the stimulated Raman effect and the microscopic theory of the scattering cross-section, and are compared with
experimental results. Output pulse powers as large as 1 kW have been measured for 10.6 and 5.3 μm excitation radiation and
continuous powers of 1 W for continuous excitation with a 5.3 μm pump source. The SFR laser offers some interesting applications
in physics and chemistry, since its frequency is proportional to the applied magnetic field and its linewidth can be made
smaller than 1 kHz. 相似文献
14.
15.
The nature of the line structure of the random lasing spectrum of vesicular films activated by dyes (rhodamine 6G, pyrromethene
597) has been analyzed. The spectral lines appear above the random lasing threshold and are manifested only within the spectrum
of the amplified spontaneous radiation of dye molecules against the continuous-pedestal background. Their intensities are
proportional to the product of the intensities of the pump and continuous spectrum at the frequencies of these lines, and
the frequencies are exactly reproduced from pulse to pulse. The shifts of the lines are strongly correlated with the pump
frequency and the frequencies of these lines coincide with the frequencies of the Raman scattering lines of dye molecules.
Using these properties, it has been shown that the observed lines are due to stimulated resonant Raman scattering by dye molecules,
which occurs simultaneously with the stimulated emission of these molecules. These two processes affect each other and jointly
form a united nonlinear process where all of the oscillations active in Raman scattering are manifested. 相似文献
16.
Selective excitation and suppression of coherent anti-Stokes Raman scattering by shaping femtosecond pulses
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Femtosecond coherent anti-Stokes Raman scattering (CARS)
suffers from poor selectivity between neighbouring Raman levels
due to the large bandwidth of the femtosecond pulses. This paper
provides a new method to realize the selective excitation and
suppression of femtosecond CARS by manipulating both the probe and
pump (or Stokes) spectra. These theoretical results indicate that
the CARS signals between neighbouring Raman levels are
differentiated from their indistinguishable femtosecond CARS spectra
by tailoring the probe spectrum, and then their selective excitation
and suppression can be realized by supplementally manipulating the
pump (or Stokes) spectrum with the $\pi $ spectral phase step. 相似文献
17.
A. F. Bunkin V. G. Mikhalevich S. M. Pershin V. N. Streltsov N. V. Tcherniega 《Physics of Wave Phenomena》2017,25(4):254-258
A theory of generation of anti-Stokes radiation on the eigenvibrations in a suspension of cylindrical nanoparticles in the field of two copropagating electromagnetic pump waves has been developed. Surface ponderomotive forces are shown to induce acoustic vibrations and dipolemoments of nanoparticles at the anti-Stokes frequency. Under these conditions, the scattering efficiency depends on the dielectric characteristics of the solution and the acoustic parameters of the liquid and solid fractions of the suspension. Experiments on stimulated low-frequency Raman scattering of laser radiation in aqueous suspensions of tobacco mosaic virus in a buffer solution have been performed. A coherent signal of the Stokes component with a frequency shift of ≈60GHz is detected; this value is in good agreement with the estimated frequency shift for stimulated excitation of eigenvibrations of cylindrical nanoparticles in a liquid: ≈50 GHz. 相似文献
18.
Highly sensitive standoff detection of explosives via backward coherent anti-Stokes Raman scattering
The detection of particles of explosives and related compounds by coherent anti-Stokes Raman scattering (B-CARS) was studied in detail. The B-CARS signal intensity was compared to that of spontaneous Raman scattering and its dependence on the distance between the sample and the detection system was found. Our measurements imply that B-CARS allows favorable detection as compared to Raman. It is estimated that for pulse energies of 10 mJ of the pump and Stokes laser beams, detection of trace amounts of samples from distances of ~10 to 200 m might be possible applying B-CARS, depending on the species. 相似文献
19.
The possibility of measuring the hydrogen impurity concentration in dense gas mixtures by coherent anti-Stokes Raman scattering
(CARS) is studied. In this technique, biharmonic laser pumping based on stimulated Raman scattering (SRS) in compressed hydrogen
is used. Because of the interference between the coherent scattering components from buffer gas molecules and molecules of
the impurity to be detected, the signal recorded may depend on the hydrogen concentration by a parabolic law, which has a
minimum and makes the results uncertain. It is shown that this uncertainty can be removed if the frequency of the biharmonic
laser pump, which is produced by the SRS oscillator, somewhat differs from the frequency of molecular oscillations of hydrogen
in the test mixture. A sensitivity of 5 ppm is obtained as applied to the hydrogen-air mixture under normal pressure. The
coefficients of the nonresonance cubic hyperpolarizability of molecules and atoms are measured relative to nitrogen in a number
of gas media. 相似文献
20.
Transient stimulated Raman scattering is used for the generation of a frequency shifted picosecond light pulse; part of this Raman shifted pulse is subsequently coherently scattered at a material excitation of a second Raman cell. Starting with the second harmonic pulse (tp = 4 ps) of a mode-locked Nd : glass laser system, both the stimulated and the coherently produced pulses have durations of 2.3 ps at different wavelengths. By the appropriate choice of the Raman medium pulses between 13 000 and 21 000 cm-1 can be generated. The coherent generation process minimizes the temporal jitter between the two pulses and allows to obtain a high time resolution of better than 0.3 ps in excite and probe experiments. 相似文献