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Photo-Modification of Melanin by a Mid-Infrared Free-Electron Laser
摘要： Melanin is rigidly constructed by several nitrogen-containing aromatic rings, and its excess accumulation in skin tissue is closely associated with melanosis. Although visible lasers (wavelength: 600–1000 nm) are conventionally used for the photo-thermolysis of melanocyte, several pigmented nevi are difficult to be treated. Here, we propose an alternate method for targeting the molecular structure of melanin using an infrared free electron laser (FEL) tuned to 5.8 μm that corresponds to the stretching vibrational mode of carboxylate group. A drastic morphological change on the black-colored surface of melanin powder were observed after the pulse irradiation with a power of 500 mJ/cm2, and the minimum irradiation time for damage to the morphology was 1.4 seconds. Analyses by mass spectroscopy, infrared spectroscopy, and 13C-nuclear magnetic resonance implied that a pyrrole group was removed by the FEL irradiation. In addition, the FEL irradiation dispersed almost all of the melanoma cells from a culture solution without any influence on other ingredients in the medium, and one-cell analysis by infrared microscopy showed that the structure of melanoma could be substantially damaged by the irradiation. This study proposes the potency of intense mid-infrared laser as novel alternative way to reduce melanin.
关键词： Infrared free electron laser,Melanoma,Vibrational mode,Melanin,Photo-modification
更新于2025-11-21 11:03:13
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Near-Infrared Fieldoscopy of Water
摘要： Linear near-infrared (NIR) spectroscopy provides information on the molecular composition, structure, and conformation, affording remarkable potential for high-resolution, in-depth, label-free biological spectro-microscopy. Broadband measurements in NIR have been carried out in the frequency domain. However, in this approach, the detection of small absorption differences is limited to the intensity noise of the source, and the detection dynamic range. We propose the concept of molecular fieldoscopy to alleviate above-mentioned limitations. Here, phase-coherent, broadband ultrashort pulse in NIR range excites molecules, afterward the transmitted electric field that carries the molecular response is directly detected by electro-optics sampling (EOS). The excitation pulse has tens of femtoseconds temporal duration, which is considerably shorter than free induction decay (FID) of the molecules under inspection. Therefore, the excitation pulse is temporally separated from the molecular response, allowing background-free measurement, and suppressing the influence of the intensity noise of the source. Moreover, measuring the complex electric field permits for extracting the full spectral phase information of the molecular response, adding a new dimension to the obtained spectroscopic data. In this work, we report about field-resolved overtone spectroscopy of water molecules in the liquid phase by using EOS to detect its first overtone vibrational mode of O-H bond appearing at 1900-1950 nm. In this respect, a carrier-envelope phase (CEP) stable, ultra-broadband spectrum covering from 700 nm to 2500 nm was directly generated from a home-built, diode-pumped Yb:YAG thin-disk regenerative amplifier. The broadband spectrum was splitted into two spectral regions: i) spectral region covering 700-1400 nm, and ii) NIR spectral region covering 1600-2500 nm. Thereafter, both regions were amplified to 25 μJ of energy, in a single-stage optical parametric amplifier and compressed to 4.8 fs and 18 fs, respectively. The 18 fs, NIR pulses were guided through a 500 μm-thick mixture of acetic acid and water. Eventually, the transmitted light was detected by EOS, containing a 50 μm-thick BBO (Type II) crystal, where the 4.8 fs pulses were used as a probe. In the absence of any sample, the measured electric field of the excitation pulses goes to zero at temporal delays above 200 fs (Fig.1a)). By adding the sample, a background-free, molecular response is observed for temporal delays beyond 200 fs, as shown in Fig.1b). The NIR response of water molecules can be clearly detected in water concentrations as low as 3%. In summary, we presented the new concept of NIR molecular fieldoscopy covering the entire molecular finger-print region. Femtosecond molecular excitation allows for background-free detection of the molecular response and higher detection sensitivity, while the heterodyne detection in EOS enhances the detection dynamic range.
关键词： electro-optics sampling,water molecules,molecular fieldoscopy,near-infrared spectroscopy,vibrational mode
更新于2025-09-11 14:15:04
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Delocalized Nonlinear Vibrational Modes in Graphene: Second Harmonic Generation and Negative Pressure
摘要： With the help of molecular dynamics simulations, delocalized nonlinear vibrational modes (DNVM) in graphene are analyzed. Such modes are dictated by the lattice symmetry, they are exact solutions to the atomic equations of motion, regardless the employed interatomic potential and for any mode amplitude (though for large amplitudes they are typically unstable). In this study, only one- and two-component DNVM are analyzed, they are reducible to the dynamical systems with one and two degrees of freedom, respectively. There exist 4 one-component and 12 two-component DNVM with in-plane atomic displacements. Any two-component mode includes one of the one-component modes. If the amplitudes of the modes constituting a two-component mode are properly chosen, periodic in time vibrations are observed for the two degrees of freedom at frequencies ω and 2ω, that is, second harmonic generation takes place. For particular DNVM, the higher harmonic can have frequency nearly two times larger than the maximal frequency of the phonon spectrum of graphene. Excitation of some of DNVM results in the appearance of negative in-plane pressure in graphene. This counterintuitive result is explained by the rotational motion of carbon hexagons. Our results contribute to the understanding of nonlinear dynamics of the graphene lattice.
关键词： molecular dynamics,nonlinear dynamics,second harmonic generation,delocalized nonlinear vibrational mode,graphene,negative pressure
更新于2025-09-10 09:29:36