Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result...Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.展开更多
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 real...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 π spectral phase step.展开更多
Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible ...Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.展开更多
Coherent anti-Stokes Raman scattering(CARS)microscopy is used to visualize the release of a model drug(theophylline)from a lipid(tripalmitin)based tablet during dissolution.The effects of transformation and dissolutio...Coherent anti-Stokes Raman scattering(CARS)microscopy is used to visualize the release of a model drug(theophylline)from a lipid(tripalmitin)based tablet during dissolution.The effects of transformation and dissolution of the drug are imaged in real time.This study reveals that the manufacturing process causes significant differences in the release process:tablets prepared from powder show formation of theophylline monohydrate on the surface which prevents a controlled drug release,whereas solid lipid extrudates did not show formation of monohydrate.This visualization technique can aid future tablet design.展开更多
This paper is the continuation of our previous research in which we studied such aspects of CARS spectroscopy in dipole-active crystals by polaritons as the regimes of coherent simultaneous propagation of three waves ...This paper is the continuation of our previous research in which we studied such aspects of CARS spectroscopy in dipole-active crystals by polaritons as the regimes of coherent simultaneous propagation of three waves (anti-Stokes, Stokes, and the pump field) to increase the efficiency of CARS as a spectroscopic method. In our previous research, we have shown the possibility of the existence of simultons at all frequencies of interacting waves. All interacting waves were supposed to be linearly polarised and plane, the medium was assumed to be nonmagnetic, and the medium was transparent at frequencies of anti-Stokes, Stokes, and the pump field (laser). The purpose of the present paper is to consider the energy carried by electromagnetic waves and its relationship with the gain factor and velocity of the simultons.展开更多
One of the significant problems of molecular spectroscopy is the determination and detailed analysis of how molecular vibrations are dephased. The dephasing of infrared-active (IR-active) vibrations of molecules was i...One of the significant problems of molecular spectroscopy is the determination and detailed analysis of how molecular vibrations are dephased. The dephasing of infrared-active (IR-active) vibrations of molecules was investigated by IR absorption spectroscopy. Pulse methods were used to investigate IR-vibrations as well. These methods revealed such coherent nonstationary effects as optical nutation, damping of the free polarization, photon echo, etc. New means of studying dephasing processes were uncovered by the method of nonstationary (time-domain) coherent anti-Stokes Raman scattering (CARS) spectroscopy. However, there are some aspects of CARS that still are not fully covered. One of them is related to Raman scattering by polaritons in dipole-active crystals whereas the second one is the increase of efficiency of CARS (minimization of the wave mismatch, the relationship between pulse width and the relaxation time, etc.). The purpose of the present research to study the case of “extreme” coherency between all interacting pulses (the duration of each pulse is smaller than characteristic times and those pulses are traveling with the same speed) in dipole-active crystals. In this research, we analyzed the process of simultaneous propagation of three waves (anti-Stokes, Stokes, and the pump) under CARS by polaritons. We have found some solutions modeling such simultaneous propagation. We also found the expression for the gain factor for such scattering. The gain factor was evaluated under the assumption of a given stationary pump field. It was shown that the typical values of the relative intensities were consistent with the experimental results.展开更多
Coherent anti-Stokes Raman scattering spectroscopy（CARS） is a well-known detecting tool in biosensing and nonlinear spectroscopy. It can provide a non-invasive alternative without the need for exogenous labels,while...Coherent anti-Stokes Raman scattering spectroscopy（CARS） is a well-known detecting tool in biosensing and nonlinear spectroscopy. It can provide a non-invasive alternative without the need for exogenous labels,while the enhancement factor for surface plasmon resonances（SPR） are extensively used to increase the local field close to the oscillators and which can obtain high enhancement. In this work, we investigate the enhancement factor of our structure for surface-enhanced coherent anti-Stokes Raman scattering. The absorption spectrum of the structure has been studied, a wide range of absorption has been realized. The enhancement can be as high as 10^（16） over standard CARS. Our design is very useful for improving the enhancement factor of surface-enhanced coherent anti-Stokes Raman scattering.展开更多
The energy dissipation mechanism of energetic materials（EMs） is very important for keeping safety. We choose nitrobenzene as a model of EM and employ transient absorption（TA） spectroscopy and time-resolved coheren...The energy dissipation mechanism of energetic materials（EMs） is very important for keeping safety. We choose nitrobenzene as a model of EM and employ transient absorption（TA） spectroscopy and time-resolved coherent anti-stokes Raman scattering（CARS） to clarify its energy dissipation mechanism. The TA data confirms that the excited nitrobenzene spends about 16 ps finishing the twist intramolecular charge transfer from benzene to nitro group, and dissipates its energy through the rapid vibration relaxation in the initial excited state. And then the dynamics of vibrational modes（VMs） in the ground state of nitrobenzene, which are located at 682 cm^-1（v1）, 854 cm^-1（v2）, 1006 cm^-1（v3）, and 1023 cm^-1（v4）,is scanned by CARS. It exhibits that the excess energy of nitrobenzene on the ground state would further dissipate through intramolecular vibrational redistribution based on the vibrational cooling of vi and v2 modes, v1 and v4 modes, and v3 and v4 modes. Moreover, the vibration-vibration coupling depends not only on the energy levels of VMs, but also on the spatial position of chemical bonds relative to the VM.展开更多
The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） tec...The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM（50.8±0.3 cm^-1） at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.展开更多
Optical microscopy with optimal axial resolution is critical for precise visualization of two-dimensional flat-top structures.Here,we present sub-diffraction-limited ultrafast imaging of hexagonal boron nitride(hBN)na...Optical microscopy with optimal axial resolution is critical for precise visualization of two-dimensional flat-top structures.Here,we present sub-diffraction-limited ultrafast imaging of hexagonal boron nitride(hBN)nanosheets using a confocal focus-engineered coherent anti-Stokes Raman scattering(cFE-CARS)microscopic system.By incorporating a pinhole with a diameter of approximately 30μm,we effectively minimized the intensity of side lobes induced by circular partial pi-phase shift in the wavefront(diameter,d0)of the probe beam,as well as nonresonant background CARS intensities.Using axial-resolution-improved cFE-CARS(acFE-CARS),the achieved axial resolution is 350 nm,exhibiting a 4.3-folded increase in the signal-to-noise ratio compared to the previous case with 0.58 d0 phase mask.This improvement can be accomplished by using a phase mask of 0.24 d0.Additionally,we employed nonde-generate phase matching with three temporally separable incident beams,which facilitated cross-sectional visualization of highly-sample-specific and vibration-sensitive signals in a pump-probe fashion with subpicosecond time resolution.Our observations reveal time-dependent CARS dephasing in hBN nanosheets,induced by Raman-free induction decay(0.66 ps)in the 1373 cm^(−1) mode.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.60878018 and 61008023)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,China (Grant No.HIT.NSRIF.2009009)the Science and Technology Innovation Foundation,Harbin,China (Grant No.RC2007QN017030)
文摘Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.
基金Project supported by Programme for Changjiang Scholars and Innovative Research Team in University(PCSIRT)Shanghai Leading Academic Discipline Project(Grant No.B408)+3 种基金National Key Project for Basic Research of China(Grant Nos.2006CB806006 and 2006CB921105)Ministry of Education of China(Grant No.30800)Shanghai Municipal Natural Science Foundation(Grant No.09ZR1409300)Shanghai Municipal Science and Technology Commission(Grant No.07DZ22025)
文摘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 π spectral phase step.
基金We gratefully acknowledge the support from the National Natural Science Foundation of China(Nos.21735006 and 21127901),and the CAS Key Technology Talent Program.
文摘Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.
基金supported by NanoNed,a nanotechnology program of the Dutch Ministry of Economic Affairs and partly financed by the Stichting voor Fundamenteel Onderzoek der Materie(FOM),which is financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek(NWO).The Marie Curie Fellowship and the Galenos Network are acknowledged for financial support(MEST-CT-2004-404992).
文摘Coherent anti-Stokes Raman scattering(CARS)microscopy is used to visualize the release of a model drug(theophylline)from a lipid(tripalmitin)based tablet during dissolution.The effects of transformation and dissolution of the drug are imaged in real time.This study reveals that the manufacturing process causes significant differences in the release process:tablets prepared from powder show formation of theophylline monohydrate on the surface which prevents a controlled drug release,whereas solid lipid extrudates did not show formation of monohydrate.This visualization technique can aid future tablet design.
文摘This paper is the continuation of our previous research in which we studied such aspects of CARS spectroscopy in dipole-active crystals by polaritons as the regimes of coherent simultaneous propagation of three waves (anti-Stokes, Stokes, and the pump field) to increase the efficiency of CARS as a spectroscopic method. In our previous research, we have shown the possibility of the existence of simultons at all frequencies of interacting waves. All interacting waves were supposed to be linearly polarised and plane, the medium was assumed to be nonmagnetic, and the medium was transparent at frequencies of anti-Stokes, Stokes, and the pump field (laser). The purpose of the present paper is to consider the energy carried by electromagnetic waves and its relationship with the gain factor and velocity of the simultons.
文摘One of the significant problems of molecular spectroscopy is the determination and detailed analysis of how molecular vibrations are dephased. The dephasing of infrared-active (IR-active) vibrations of molecules was investigated by IR absorption spectroscopy. Pulse methods were used to investigate IR-vibrations as well. These methods revealed such coherent nonstationary effects as optical nutation, damping of the free polarization, photon echo, etc. New means of studying dephasing processes were uncovered by the method of nonstationary (time-domain) coherent anti-Stokes Raman scattering (CARS) spectroscopy. However, there are some aspects of CARS that still are not fully covered. One of them is related to Raman scattering by polaritons in dipole-active crystals whereas the second one is the increase of efficiency of CARS (minimization of the wave mismatch, the relationship between pulse width and the relaxation time, etc.). The purpose of the present research to study the case of “extreme” coherency between all interacting pulses (the duration of each pulse is smaller than characteristic times and those pulses are traveling with the same speed) in dipole-active crystals. In this research, we analyzed the process of simultaneous propagation of three waves (anti-Stokes, Stokes, and the pump) under CARS by polaritons. We have found some solutions modeling such simultaneous propagation. We also found the expression for the gain factor for such scattering. The gain factor was evaluated under the assumption of a given stationary pump field. It was shown that the typical values of the relative intensities were consistent with the experimental results.
基金Project supported by the National Key Research Program of China(No.2011ZX01015-001)the National Basic Research Program of China(Nos.2011CBA00608,2012CB619203,2015CB351902,2015CB932402)
文摘Coherent anti-Stokes Raman scattering spectroscopy（CARS） is a well-known detecting tool in biosensing and nonlinear spectroscopy. It can provide a non-invasive alternative without the need for exogenous labels,while the enhancement factor for surface plasmon resonances（SPR） are extensively used to increase the local field close to the oscillators and which can obtain high enhancement. In this work, we investigate the enhancement factor of our structure for surface-enhanced coherent anti-Stokes Raman scattering. The absorption spectrum of the structure has been studied, a wide range of absorption has been realized. The enhancement can be as high as 10^（16） over standard CARS. Our design is very useful for improving the enhancement factor of surface-enhanced coherent anti-Stokes Raman scattering.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21573094,11274142,11474131,11574112,and 51502109)the National Found for Fostering Talents of Basic Science,China(Grant No.J1103202)+1 种基金the Science Challenging Program(Grant No.JCKY2016212A501)China Scholarship Council(CSC) during a visit of Ning Sui(Grant No.201706175038) to MPIA is also acknowledged
文摘The energy dissipation mechanism of energetic materials（EMs） is very important for keeping safety. We choose nitrobenzene as a model of EM and employ transient absorption（TA） spectroscopy and time-resolved coherent anti-stokes Raman scattering（CARS） to clarify its energy dissipation mechanism. The TA data confirms that the excited nitrobenzene spends about 16 ps finishing the twist intramolecular charge transfer from benzene to nitro group, and dissipates its energy through the rapid vibration relaxation in the initial excited state. And then the dynamics of vibrational modes（VMs） in the ground state of nitrobenzene, which are located at 682 cm^-1（v1）, 854 cm^-1（v2）, 1006 cm^-1（v3）, and 1023 cm^-1（v4）,is scanned by CARS. It exhibits that the excess energy of nitrobenzene on the ground state would further dissipate through intramolecular vibrational redistribution based on the vibrational cooling of vi and v2 modes, v1 and v4 modes, and v3 and v4 modes. Moreover, the vibration-vibration coupling depends not only on the energy levels of VMs, but also on the spatial position of chemical bonds relative to the VM.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21673211 and 21203047)the Foundation of Heilongjiang Bayi Agricultural University,China(Grant No.XZR2014-16)the Science Challenging Program of China(Grant No.JCKY2016212A501)
文摘The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM（50.8±0.3 cm^-1） at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.
基金National Research Foundation of Korea(2023R1A2C100531711)H.K.also acknowledges support from the DGIST R&D programs(22-CoENT-01 and 22-BT-06)funded by the Ministry of Science and ICT.V.R.acknowledges support from Department of Science and Technology(DST)Indo-Korea joint research project(INT/Korea/P-44).
文摘Optical microscopy with optimal axial resolution is critical for precise visualization of two-dimensional flat-top structures.Here,we present sub-diffraction-limited ultrafast imaging of hexagonal boron nitride(hBN)nanosheets using a confocal focus-engineered coherent anti-Stokes Raman scattering(cFE-CARS)microscopic system.By incorporating a pinhole with a diameter of approximately 30μm,we effectively minimized the intensity of side lobes induced by circular partial pi-phase shift in the wavefront(diameter,d0)of the probe beam,as well as nonresonant background CARS intensities.Using axial-resolution-improved cFE-CARS(acFE-CARS),the achieved axial resolution is 350 nm,exhibiting a 4.3-folded increase in the signal-to-noise ratio compared to the previous case with 0.58 d0 phase mask.This improvement can be accomplished by using a phase mask of 0.24 d0.Additionally,we employed nonde-generate phase matching with three temporally separable incident beams,which facilitated cross-sectional visualization of highly-sample-specific and vibration-sensitive signals in a pump-probe fashion with subpicosecond time resolution.Our observations reveal time-dependent CARS dephasing in hBN nanosheets,induced by Raman-free induction decay(0.66 ps)in the 1373 cm^(−1) mode.
