Time-resolved Raman Spectroscopy Research Articles

Observation of laser-driven shock propagation by nanosecond time-resolved Raman spectroscopy

An improved nanosecond time-resolved Raman spectroscopy is performed to observe laser-driven shock propagation in the anthracene/epoxy glue layer. The digital delay instead of optical delay line is introduced for sake of unlimited time range of detection, which enables the ability to observe both shock loading and shock unloading that always lasts several hundred nanoseconds. In this experiment, the peak pressure of shock wave, the pressure distribution, and the position of shock front in gauge layer were determined by fitting Raman spectra of anthracene using the Raman peak shift simulation. And, the velocity of shock wave was calculated by the time-dependent position of shock front.

Time-resolved X-ray diffraction and Raman studies of the phase transition mechanisms of methane hydrate.

The mechanisms by which methane hydrate transforms from an sI to sH structure and from an sH to filled-ice Ih structure were examined using time-resolved X-ray diffractometry (XRD) and Raman spectroscopy in conjunction with charge-coupled device camera observation under fixed pressure conditions. The XRD data obtained for the sI-sH transition at 0.8 GPa revealed an inverse correlation between sI and sH, suggesting that the sI structure is replaced by sH. Meanwhile, the Raman analysis demonstrated that although the 12-hedra of sI are retained, the 14-hedra are replaced sequentially by additional 12-hedra, modified 12-hedra, and 20-hedra cages of sH. With the sH to filled-ice Ih transition at 1.8 GPa, both the XRD and Raman data showed that this occurs through a sudden collapse of the sH structure and subsequent release of solid and fluid methane that is gradually incorporated into the filled-ice Ih to complete its structure. This therefore represents a typical reconstructive transition mechanism.

In situ tracking of defect healing and purification of single-wall carbon nanotubes with laser radiation by time-resolved Raman spectroscopy

Fine-tuned localised laser heating of pristine or mechanically dispersed (for composite processing) SWCNTs resulting in precision healing and purification.

J2210406 静電駆動MEMS光チョッパを用いた時間分解顕微ラマン応力測定

A high speed MEMS optical chopper has been developed for time-resolved micro Raman spectroscopy to measure dynamic stress of single crystal silicon resonators. The chopper was fabricated using a silicon-on-glass structure, in which the stationary shutter is made of aluminum film on the glass substrate and the moving chopper is formed in the silicon device layer. The chopper is actuated by electrostatic force using slanted parallel plate electrodes. The chopper was used for modulating the incident laser light directly putting in the optics of a commercial micro Raman spectrometer. The modulation of incident light at 1 kHz, 10 % duty ratio and the extinction ratio of 5.6 were realized for measuring an out-of-plane silicon resonator made from a silicon-on-insulator wafer resonated at 1 kHz. The dynamic stress was measured and the stress change of 569 MPa was measured.

Appearance of annular ring-like intermediates during amyloid fibril formation from human serum albumin.

The self-assembly of proteins triggered by a conformational switch into highly ordered β-sheet rich amyloid fibrils has captivated burgeoning interest in recent years due to the involvement of amyloids in a variety of human diseases and a diverse range of biological functions. Here, we have investigated the mechanism of fibrillogenesis of human serum albumin (HSA), an all-α-helical protein, using an array of biophysical tools that include steady-state as well as time-resolved fluorescence, circular dichroism and Raman spectroscopy in conjunction with atomic force microscopy (AFM). Investigations into the temporal evolution of nanoscale morphology using AFM revealed the presence of ring-like intermediates that subsequently transformed into worm-like fibrils presumably by a ring-opening mechanism. Additionally, a multitude of morphologically-diverse oligomers were observed on the pathway to amyloid formation. Kinetic analysis using multiple structural probes in-tandem indicated that HSA amyloid assembly is a concerted process encompassing a major structural change that is primarily mediated by hydrophobic interactions between thermally-induced disordered segments originating in various domains. A slower growth kinetics of aggregates suggested that the protein structural reorganization is a prerequisite for fibril formation. Moreover, time-dependent Raman spectroscopic studies of HSA aggregation provided key molecular insights into the conformational transitions occurring within the protein amide backbone and at the residue-specific level. Our data revealed the emergence of conformationally-diverse disulfides as a consequence of structural reorganization and sequestration of tyrosines into the hydrophobic amyloid core comprising antiparallel cross β-sheets.

Controlling the Catalytic Efficiency on the Surface of Hollow Gold Nanoparticles by Introducing an Inner Thin Layer of Platinum or Palladium

The efficiency of heterogeneous catalysis of electron-transfer reactions on the surface of gold nanoshells was changed by adding an inner platinum or palladium nanoshell in the double-shell nanocatalysts. The reduction of 4-nitrothiophenol (4NTP) by borohydride was studied as a model reaction. To confirm the heterogeneous catalytic mechanism, the nanocatalysts were assembled into a monolayer on the surface of a quartz substrate using the Langmuir-Blodgett technique, and the 4NTP was allowed to bind to the surface of gold through a strong thiol bond. The stages of the reduction reaction of 4NTP on the surface of gold were successfully followed by time-resolved surface-enhanced Raman spectroscopy. Palladium was found to increase the catalytic efficiency of the gold surface due to the presence of a new Fermi level of the palladium-gold alloy, while platinum decreased its catalytic efficiency due to the electron-withdrawing effect of platinum atoms, which resulted from the difference in their electrochemical reduction potentials.

Molecular vibrational dynamics in PMMA studied by femtosecond CARS

The ultrafast molecular vibrational dynamics in PMMA sheets is studied by femtosecond time-resolved coherent anti-Stokes Raman spectroscopy at room temperature. The C – H stretch modes at 2870 cm-1 and 3008 cm-1 in PMMA sheets are excited and detected. The coherence relaxation times and beat wavenumbers of the Raman modes are obtained.

Solvent-Triggered Crystallization of Polymorphs Studied in Situ

The crystallization of a highly polymorphic compound was studied in situ by combined time-resolved X-ray diffraction and Raman spectroscopy. Any influences of solid surfaces, temperature, and humidity on the crystallization were omitted by the use of a specially designed acoustic levitator. Investigations of polymorphic phase transitions during the crystallization process in different solvents allowed a structure assignment from first crystalline assemblies to final crystalline form. For the first time, it was possible to yield pure phases of selected polymorphs of the model compound ROY (5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile) directly from solution. The influence of the solvent on the final products and transient phases during the crystallization process was elucidated.

Molecular vibrational dynamics in ethanol studied by femtosecond CARS

Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is utilized to study the ultrafast vibrational dynamics in ethanol at room temperature. The beat wavenumbers between Raman modes of CH stretch modes (from 2800cm−1 to 3000cm−1) in ethanol are excited and detected by varying wavelengths of the laser pulses and detection window. The coherence relaxation times of the CH stretch mode in ethanol are measured.

Coherent spin–rotational dynamics of oxygen superrotors

We use state- and time-resolved coherent Raman spectroscopy to study the rotational dynamics of oxygen molecules in ultra-high rotational states. While it is possible to reach rotational quantum numbers up to by increasing the gas temperature to 1500 K, low population levels and gas densities result in correspondingly weak optical response. By spinning molecules with an optical centrifuge, we efficiently excite extreme rotational states with in high-density room temperature ensembles. Fast molecular rotation results in the enhanced robustness of the created rotational wave packets against collisions, enabling us to observe the effects of weak spin–rotation coupling in the coherent rotational dynamics of oxygen. The decay rate of spin–rotational coherence due to collisions is measured as a function of the molecular angular momentum and its dependence on the collisional adiabaticity parameter is discussed. We find that at high values of N, the rotational decoherence of oxygen is much faster than that of the previously studied non-magnetic nitrogen molecules, pointing at the effects of spin relaxation in paramagnetic gases.

Molecular vibrational dynamics in water studied by femtosecond coherent anti-Stokes Raman spectroscopy

We utilized femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to study the ultrafast vibrational dynamics in distilled water at room temperature. The CARS signals from the broad OH-stretching modes between 3100cm−1 and 3700cm−1 were obtained and analyzed. The dephasing times of four Raman modes in water were detected and compared.

Time-resolved coherent Raman spectroscopy by high-speed pump-probe delay scanning.

Using a spinning window pump-probe delay scanner, we demonstrate a means of acquiring time-resolved vibrational spectra at rates up to 700 Hz. The time-dependent phase shift accumulated by the probe pulse in the presence of a coherently vibrating sample gives rise to a Raman-induced frequency shifting readily detectable in a balanced detector. This rapid delay scanning system represents a 23-fold increase in averaging speed and is >10× faster than state-of-the-art voice coil delay lines. These advancements make pump-probe spectroscopy a more practical means of imaging complex media.

Melting and phase transitions of nitrogen under high pressures and temperatures.

Dense nitrogen exhibits fascinating molecular and extended polymorphs as well as an anomalous melt maximum at high temperatures. However, the exact solid-liquid phase boundary is still the subject of debate, as both creating and probing hot dense nitrogen, solid and fluid alike, poses unique experimental challenges. Raman studies of nitrogen were performed to investigate the melting curve and solid-solid phase transitions in the pressure-temperature range of 25 to 103 GPa and 300 to 2000 K. The solid-liquid phase boundary has been probed with time-resolved Raman spectroscopy on ramp heated nitrogen in diamond anvil cell (DAC), showing a melting maximum at 73 GPa and 1690 K. The solid-solid phase boundaries have been measured with spatially resolved micro-confocal Raman spectroscopy on resistively heated DAC, probing the δ-ɛ phase line to 47 GPa and 914 K. At higher pressures the θ-phase was produced upon a repeated thermal heating of the ζ-phase, yet no evidence was found for the ι-phase. Hence, the present results signify the path dependence of dense nitrogen phases and provide new constraints for the phase diagram.

Characterization of a conical intersection in a charge-transfer dimer with two-dimensional time-resolved stimulated Raman spectroscopy.

Photochemical reactions are mediated by conical intersections (CI), which are difficult to directly probe and characterize. To gain insight into CIs, two-dimensional femtosecond stimulated Raman spectroscopy (2D-FSRS) is used to examine a model excited-state charge-transfer (CT) complex consisting of an electron donor, tetramethylbenzene (TMB), and an acceptor, tetracyanoquinodimethane (TCNQ). Following impulsive excitation, the excited-state transient absorption reveals large-amplitude excited-state wave packet motion along low-frequency modes, in particular TCNQ's totally symmetric 323 cm(-1) CCN bend, which persist for ∼5 ps. These low-frequency coherences modulate the intensity and peak frequencies of the excited-state FSRS vibrational spectra. In particular, large-magnitude oscillations at 323 cm(-1) are observed in the peak frequency (Δω = 2 cm(-1)) and intensity (ΔOD = 1.5 mOD) of the nontotally symmetric 1271 cm(-1) C═C rocking mode. The magnitude of these oscillations is analyzed to determine the first-order anharmonic coupling between the high- and low-frequency degrees of freedom in the excited state. The anharmonic coupling between the totally symmetric 323 cm(-1) and the nontotally symmetric 1271 cm(-1) modes is estimated to be in excess of 50 cm(-1), strongly suggesting that they are the tuning and coupling modes, respectively, for the CI that connects the CT excited state to the neutral ground state and controls charge recombination internal conversion.

Influence of geometrical configuration on molecular vibrational dynamics in BBO crystals studied by femtosecond CARS

Abstract Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy is utilized to study the ultrafast vibrational dynamics in BBO crystals at room temperature. The beat wavenumbers between Raman modes and coherence decay rates of Raman modes (at 1214 cm −1 and 1437 cm −1 ) in BBO crystals are excited and detected. The intensities of vibrational modes in BBO crystals are found that they can be controlled by geometrical configuration.

Relaxation mechanism of β-carotene from S2 (1Bu(+)) state to S1 (2Ag(-)) state: femtosecond time-resolved near-IR absorption and stimulated resonance Raman studies in 900-1550 nm region.

Carotenoids have two major low-lying excited states, the second lowest (S2 (1Bu(+))) and the lowest (S1 (2Ag(-))) excited singlet states, both of which are suggested to be involved in the energy transfer processes in light-harvesting complexes. Studying vibrational dynamics of S2 carotenoids requires ultrafast time-resolved near-IR Raman spectroscopy, although it has much less sensitivity than visible Raman spectroscopy. In this study, the relaxation mechanism of β-carotene from the S2 state to the S1 state is investigated by femtosecond time-resolved multiplex near-IR absorption and stimulated Raman spectroscopy. The energy gap between the S2 and S1 states is estimated to be 6780 cm(-1) from near-IR transient absorption spectra. The near-IR stimulated Raman spectrum of S2 β-carotene show three bands at 1580, 1240, and 1050 cm(-1). When excess energy of 4000 cm(-1) is added, the S1 C═C stretch band shows a large upshift with a time constant of 0.2 ps. The fast upshift is explained by a model that excess energy generated by internal conversion from the S2 state to the S1 state is selectively accepted by one of the vibronic levels of the S1 state and is redistributed among all the vibrational modes.

Probing dynamic crystal growth of compressed hydrogen using dynamic-DAC, time-resolved spectroscopy and highspeed micro-photography

Solidification and crystal growth processes of hydrogen (H2) have been studied under dynamic compression using dynamic-DAC (dDAC) in conjunction with time resolved Raman spectroscopy and high-speed microphotography. Liquid H2 was compressed at a compression rate of 43 GPa/s across the liquid/solid phase boundary, causing a discontinuous vibron shift at the onset of solidification. The real time sample images, on the other hand, showed that H2 solidifies into a characteristic, grain boundary free crystal, formed initially from the outside (or the edge of liquid) then grew into the central area within 11 ms. Interestingly, the time scale associated with the glassy solid formation is in good agreement with that of the discontinuous Raman frequency shift. The rate of crystal growth was measured to be 0.3 cm/s.

Molecular vibrational dynamics of rhodamine B dye in solution studied by femtosecond CARS

Spectrally dispersed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy is utilized to study the ultrafast vibrational dynamics in rhodamine B dye in solution at room temperature. The anti-Stokes intensities are monitored as a function of time and wavenumber. By simply changing the timing of laser pulses, the vibrational dynamics of excited Raman transitions in rhodamine B molecules can be tracked and detected.

Effects of a protic ionic liquid on the reaction pathway during non-aqueous sol-gel synthesis of silica: a Raman spectroscopic investigation.

The reaction pathway during the formation of silica via a two-component “non-aqueou” sol-gel synthesis is studied by in situ time-resolved Raman spectroscopy. This synthetic route is followed with and without the addition of the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide (C2HImTFSI) in order to investigate its effect on the reaction pathway. We demonstrate that Raman spectroscopy is suitable to discriminate between different silica intermediates, which are produced and consumed at different rates with respect to the point of gelation. We find that half-way to gelation monomers and shorter chains are the most abundant silica species, while the formation of silica rings strongly correlates to the sol-to-gel transition. Thus, curling up of linear chains is here proposed as a plausible mechanism for the formation of small rings. These in turn act as nucleation sites for the condensation of larger rings and thus the formation of the open and polymeric silica network. We find that the protic ionic liquid does not change the reaction pathway per se, but accelerates the cyclization process, intermediated by the faster inclusion of monomeric species.

J2240206 時間分解顕微ラマン分光のための両側静電駆動MEMS光チョッパ([J224-02]『マイクロ・ナノ機械の信頼性』のための材料創製・測定・解析技術 マイクロ・ナノ実験力学と機能材料)

In this report, we propose a double-side-drive MEMS optical chopper for time-resolved micro Raman spectroscopy to evaluate the local dynamic stress of Si resonators. The chopper is used as a mechanical pulse width modulator for the incident laser installed to a commercial micro Raman spectrometer. The advantages are; 1) mechanical chopping, which can maintain the quality of source incident laser 2) small size for easy installation to the Raman spectrometer 3) low cost and low voltage operation. The chopper fabricated using silicon on glass (SOG) with alignment anodic bonding process was operated by electrostatic force using tilted comb electrodes. The measured mechanical response has no overshooting and the response time was about 32 μs. This result satisfies the requirement for the dynamic stress measurement of silicon structure resonating up to 1 kHz. The measured optical response showed that the incident laser was modulated but the extinction ratio of modulated laser was low due to stray light.