Periodically intensity-modulated pulses by optical parametric amplification for multicycle tunable terahertz pulse generation

The superposition of signal and idler pulses in dual- chirped optical parametric amplification is proposed for the efficient generation of intensity-modulated pulses with periodic modulation. Both the duration and the modulation period are easily and independently adjustable. Numerical simulations for a three-stage optical parametric amplifier system predicted an efficiency as high as ~50% for about 40 mJ of output pulse energy at a wavelength of 2 μm. Sources of such intensity-modulated pulses near 1.6 μm or 2 μm wavelength, pumped by Ti:sapphire or Yb-doped lasers, can be ideally suited for intense multicycle THz pulse generation with tunable frequency and bandwidth by optical rectification for example in organic, semiconductor, or lithium niobate materials

The effect of the flexibility of hydrogen bonding network on low-frequency motions of amino acids. Evidence from Terahertz spectroscopy and DFT calculations

Low-frequency modes of l-Asp and l-Asn were studied in the range from 0.1 to 3.0 THz using time-domain Terahertz spectroscopy and density functional theory calculation. The results show that PBE-D2 shows more success than BLYP-D2 in prediction of THz absorption spectra. To compare their low-frequency modes, we adopted ”vibrational character ID strips” proposed by Schmuttenmaer and coworkers [Journal of Physical Chemistry B, 117, 10444(2013)]. We found that the most intense THz absorption peaks of two compounds both involve severe distortion of their hydrogen bonding networks. Due to less rigid hydrogen bonding network in l-Asp, the side chain (carboxyl group) of l-Asp exhibits larger motions than that (carboxamide group) of l-Asn in low-frequency modes