Yu Huang

Texas A&M University, College Station, TX, United States

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Publications (7)41.51 Total impact

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    ABSTRACT: We investigate femtosecond coherent anti-Stokes Raman scattering (CARS) signals collected at range from dipicolinic acid (DPA), one of the marker molecules within anthrax spores. The backscattered CARS signal from the DPA solution recorded versus probe pulse delay exhibits molecular coherence beating. We show a signal-to-noise ratio better than two orders of magnitude for a sample placed 12 m away, and infer the possibility of detection at range over distances of hundreds of metres. We also study the backscattered CARS signals from DPA powder. The beat signal exhibits two vibrational modes with a level spacing of 70±10 cm− 1, which matches very well with the literature value of 69 cm− 1. We quantitatively study the effects of multiple scattering in four-wave mixing from powder samples and estimate an 8 µm mean distance between the scattering events.
    Journal of Modern Optics 11/2007; 54(Nos. 16-17):2473-2480. · 1.16 Impact Factor
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    ABSTRACT: We demonstrate a novel technique for three-color time-resolved coherent anti-Stokes Raman scattering using a Ti:Sapphire oscillator and four-wave mixing in a photonic crystal fiber. We measure vibrational coherence decays in calcite and several molecules. Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) measurements provide chemical information by recording the molecular vibrational dynamics in the time domain. In a fs-CARS experiment, the molecules are excited to one or more Raman-active vibrational modes by two coherent laser pulses, namely pump and Stokes pulses. The created vibrational coherence due to the Raman excitation is subsequently probed by a delayed third pulse, and generates a CARS signal, which is resonantly enhanced when the difference frequency between the pump and Stokes pulses matches with the frequency of a Raman transition, providing chemical information of the sample. Complicated and costly laser systems such as two optical parametric amplifiers with a Ti:Sapphire regenerative amplifier system are usually used to generate different wavelengths. Recently however, there is an emerging interest in multi-wavelength pulses generation through the nonlinear interaction between Ti:Sapphire oscillator and a photonic crystal fiber (PCF), taking advantage of the continuum and/or soliton generation in PCF.[1-4] Fig. 1a. Experimental setup (left) and b. The pump, Stokes, and probe beam spectra as generated in the PCF. The inset shows the cross-correlation between the generated Stokes and probe, with a temporal resolution of 200fs.
    05/2007;
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    ABSTRACT: We demonstrate a real-time method with high sensitivity and high selectivity for detection of Anthrax-surrogate spores using Coherent Anti-Stokes Raman Scattering. We reliably detect spores in less than 50 ms based on their vibrational spectra.
    05/2007;
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    ABSTRACT: We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.
    Science 05/2007; 316(5822):265-8. · 31.20 Impact Factor
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    ABSTRACT: Measurements of the beat frequencies between vibrational modes of dipicolinic acid (DPA) and a series of other molecules (interferents) are presented. The results were obtained from femtosecond time-resolved coherent Raman scattering, and the vibrational level spacings were determined from a Fourier transform of the signal versus probe pulse delay. The entire spectrum of the generated signal is recorded in order to demonstrate multimode excitation and to explain the variety of qualitatively different traces that can be obtained for the same molecule. Since the spectral signature of DPA is unique enough to be used for identification purposes, this technique has the potential to detect hazardous bacterial species, such as anthrax spores.
    Journal of Applied Physics 12/2006; 100(12):124912-124912-5. · 2.21 Impact Factor
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    ABSTRACT: We demonstrate that femtosecond ultraviolet and visible coherent anti-Stokes Raman spectroscopy provides the sensitivity and specificity needed to distinguish between two similar molecules of pyridinedicarboxylic acid. The Fourier transforms of the temporal measurements provide the energy difference between the ground state vibrational modes. Quantum chemical calculations provide theoretical predictions that agree well with the measurements. The present technique allows us to distinguish 10 cm(-1) frequency shifts by using pulses ten times broader than the shifts.
    Optics Letters 12/2006; 31(21):3176-8. · 3.39 Impact Factor
  • Yu Huang, Arthur Dogariu
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    ABSTRACT: We apply an adaptive feedback loop to control a ultra-violet (UV) femtosecond pulse shaping apparatus. The adaptive feedback control is implemented by a continuous parameter genetic algorithm. We use the adaptive shaper to compensate for the pulse chirp. The genetic algorithm produces a pulse with a width of 115 fs, identical to that of the transformlimited pulse. We then apply the adaptive shaper to the Stokes pulse in a femtosecond coherent anti-Stokes Raman scattering (CARS) experiment on dipicolinic acid solution. The algorithm maximizes the first CARS beat signal at the probe pulse delay of 650 fs. We confirm that a transformlimited Stokes pulse achieves the best detection sensitivity.
    Optics Express 11/2006; 14(21):10089-94. · 3.55 Impact Factor