Detection of broadband terahertz waves with a laser-induced plasma in gases

Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
Physical Review Letters (Impact Factor: 7.73). 10/2006; 97(10):103903. DOI: 10.1103/PHYSREVLETT.97.103903
Source: PubMed

ABSTRACT We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.


Available from: Jianming Dai, Jan 15, 2014
1 Follower
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The broadband complex conductivities of transparent conducting oxides (TCO), namely aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by terahertz time domain spectroscopy (THz-TDS) in the frequency range from 0.5 to 18 THz using air plasma techniques, supplemented by the photoconductive antenna (PCA) method. The complex conductivities were accurately calculated using a thin film extraction algorithm and analyzed in terms of the Drude conductivity model. All the measured TCOs have a scattering time below 15 fs. We find that a phonon response must be included in the description of the broadband properties of AZO and GZO for an accurate extraction of the scattering time in these materials, which is strongly influenced by the zinc oxide phonon resonance tail even in the low frequency part of the spectrum. The conductivity of AZO is found to be more thickness dependent than GZO and ITO, indicating high importance of the surface states for electron dynamics in AZO. Finally, we measure the transmittance of the TCO films from 10 to 200 THz with Fourier transform infrared spectroscopy (FTIR) measurements, thus closing the gap between THz-TDS measurements (0.5-18 THz) and ellipsometry measurements (200-1000 THz).
    Optical Materials Express 03/2015; 5(3). DOI:10.1364/OME.5.000566 · 2.92 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The methodology and principle using vibrational energy transfer to measure molecular distances in liquids are introduced. The application of the method to the studies of ion pairing and clustering in strong electrolyte aqueous solutions is demonstrated with MSCN aqueous solutions where M = Li, Na, K, Cs, and NH4. Experiments suggest that ions in the concentrated aqueous solutions can form substantial quantities of ion clusters in which both cations and anions are involved. More and larger clusters form in solutions that are relatively more concentrated and which include a larger cation. In KSCN solutions, the shortest anionic distance in the ion clusters is the same as that in the KSCN crystal. The rotational time of the anion and the nonresonant vibrational energy transfer time with a gap of 75 cm-1 in the KSCN saturated solution are very similar to those in the KSCN crystal. However, the KSCN ion clusters are closer in structure to the melt. The clusters form an interconnected network with random ionic orientations. Because of ion clustering, the anion and water dynamics behave distinctly in the same solutions. At high concentrations, the anion rotation significantly slows down because of the increase in the size of the ion clusters, but the slowdown amplitude of water rotation is very modest because many of the water molecules still remain in the "bulk" state due to ion clustering. The rotational dynamics of both water and anions are slower in a solution with a smaller cation, primarily because a smaller cation has a stronger cation/anion interaction and a cation/water interaction that leads to more water molecules confined in the ion clusters. Adding ions or molecules into the KSCN solutions can perturb the ion clusters. Weakly hydrated anions can participate in clustering and form mixed ion clusters with KSCN, and strongly hydrated anions can reduce the effective water molecules solvating KSCN and facilitate the formation of more and larger KSCN ion clusters. Similarly, molecules which can strongly bind to SCN- prefer to participate in the KSCN ion clusters. Molecules which are strongly hydrated prefer to remain hydrated and facilitate the ion clustering of KSCN.
    The Journal of Physical Chemistry B 02/2015; 119(12). DOI:10.1021/jp512320a · 3.38 Impact Factor
  • Physics of Plasmas 07/2014; 21:073104. DOI:10.1063/1.4890852 · 2.25 Impact Factor