Takayuki Suzuki

Femtosecond time-resolved X-ray absorption spectroscopy of liquid using a hard X-ray free electron laser in a dual-beam dispersive detection method

We present femtosecond time-resolved X-ray absorption spectroscopy of aqueous solution using a hard x-ray free electron laser (SACLA) and a synchronized Ti:sapphire laser. The instrumental response time is 200 fs, and the repetition rate of measurement is 10 Hz. A cylindrical liquid beam 100 μm in diameter of aqueous ammonium iron(III) oxalate solution is photoexcited at 400 nm, and the transient X-ray absorption spectra are measured in the K-edge region of iron, 7.10 - 7.26 keV, using a dual X-ray beam dispersive detection method. Each of the dual beams has the pulse energy of 1.4 μJ, and pump-induced absorbance change on the order of 10(-3) is successfully detected. The photoexcited iron complex exhibits a red shifted iron K-edge with the appearance time constant of 260 fs. The X-ray absorption difference spectra, with and without the pump pulses, are independent of time delay after 1.5 ps up to 100 ps, indicating that the photoexcited species is long-lived.

Efficient heterodyne CARS measurement by combining spectral phase modulation with temporal delay technique

We propose and demonstrate an improved heterodyne coherent anti-Stokes Raman scattering (CARS) measurement with a rapid phase modulation and temporal displacement of the background, to simplify signal extraction and effectively reduce a nonresonant background (NRB). This method is a modification of the single-beam CARS spectroscopy originally proposed by Oron et al. in which a narrowband phase modulation is used to enhance contrast between resonant signals and the NRB through heterodyne detection [Phys. Rev. Lett. 89, 273001 (2002)]. In our scheme, a large delay between the narrow- and broadband components enables us to reduce the NRB while maintaining signal enhancement by heterodyne detection. We develop a frequency-resolved Michelson interferometer in which the narrow- and broadband components are spatially separated and recombined with an arbitrary delay. We show that sharp Raman lines can be obtained from chloroform molecules by the observation of difference spectra and phase sensitive detection. The spectral resolution achieved, which is limited by that of the spectrometer we used, is < 8 cm(-1). This method can potentially be extended to make real-time measurements by further developing a spectrometer that directly accumulates difference spectra.

Interferometric polarization pulse shaper stabilized by an external laser diode for arbitrary vector field shaping.

We achieved reliable and stable generation of pulses with all possible polarization states by a Mach-Zehnder pulse shaper. This was realized by incorporating a stabilization mechanism using an external laser diode in the interferometric pulse shaper. This stabilization mechanism has overcome an inherent instability in the Mach-Zehnder interferometer, which caused serious distortion of shaped pulses. For a demonstration of polarization shaping, we generated and measured chiral pulses with a rotating major axis of polarizing orientations at arbitrary frequencies. We expect these chiral pulses enables us to study on new chirality-related light-matter interactions.

In vivo molecular labeling of halogenated volatile anesthetics via intrinsic molecular vibrations using nonlinear Raman spectroscopy

Halogenated volatile anesthetics are frequently used for inhaled anesthesia in clinical practice. No appropriate biological method has been available for visualizing their localization in action. Therefore, despite their frequent use, the mechanism of action of these drugs has not been fully investigated. We measured coherent anti-Stokes Raman scattering (CARS) spectra of sevoflurane and isoflurane, two of the most representative volatile anesthetics, and determined the low-frequency vibrational modes without nonresonant background disturbance. Molecular dynamics calculations predict that these modes are associated with multiple halogen atoms. Because halogen atoms rarely appear in biological compounds, the entire spectral landscape of these modes is expected to be a good marker for investigating the spatial localization of these drugs within the intracellular environment. Using live squid giant axons, we could detect the unique CARS spectra of sevoflurane for the first time in a biological setting.

In Vivo Molecular Labeling of Halogenated Volatile Anesthetics via Intrinsic Molecular Vibrations using Nonlinear Raman Spectroscopy

Halogenated volatile anesthetics are frequently used for inhaled anesthesia in clinical practice. No appropriate biological method has been available for visualizing their localization in action. Therefore, despite their frequent use, the mechanism of action of these drugs has not been fully investigated. We measured coherent anti-Stokes Raman scattering (CARS) spectra of sevoflurane and isoflurane, two of the most representative volatile anesthetics, and determined the low-frequency vibrational modes without nonresonant background disturbance. Molecular dynamics calculations predict that these modes are associated with multiple halogen atoms. Because halogen atoms rarely appear in biological compounds, the entire spectral landscape of these modes is expected to be a good marker for investigating the spatial localization of these drugs within the intracellular environment. Using live squid giant axons, we could detect the unique CARS spectra of sevoflurane for the first time in a biological setting.

Improved signal extraction method for single-pulse heterodyne CARS spectroscopy

Single-pulse heterodyne CARS (coherent anti-Stokes Raman scattering) detection scheme using shaped femtosecond pulses is one of the most sophisticated approach for managing the problem of non-resonant background disturbance in CARS measurement. However, with the signal processing method conducted in the original report,1-3 we found that background suppression and resonant peak extraction were sometimes difficult and incomplete. We discuss the reason of this unsuccessful signal processing and propose an improved method for signal extraction realizing the better quality of extracted spectra.

Heterodyne CARS measurement of inhalational anesthetic molecules using adaptively phase-modulated femtosecond pulses

Inhalational anesthetic is important clinically, especially for surgical operations. However, the molecular mechanism of their action has not been completely clarified, because these anesthetic molecules are small, and hence, difficult in labeling in cells. To visualize their distribution in the cell and to examine in-vivo behavior of such a halogenated anesthetic, label-free biomedical imaging with molecular specificity is required.

Extreme nonresonant background reduction for rapid phase-modulation CARS spectroscopy by phase sensitive detection

We effectively suppressed a nonresonant background, which is general issue of femtosecond-laser based multiplex CARS spectroscopy, by applying phase sensitive detection for our rapid phase-modulation CARS method [3]. The modulation phase of each spectral measurement can be extracted from an interference intensity between a narrowband probe and a broadband pulse. We demonstrated the method with a sample of chloroform molecules. By using a phase sensitive detection, signal-to-noise ratio was improved from 2.7 to 9.4 dB.