We propose a nonlinear optical crystal-based compact terahertz (THz) - microfluidic chip with a few arrays of metaatoms for the ultra-trace sensing of solutions. We design the meta-atom array to induce natural evolutional resonance with a point THz source. The point THz source is locally generated by optical rectification at the irradiation spot of a femtosecond pulse laser beam in the single meta-atom, which induces a tightly electric field confinement mode. The generated THz waves resonate with surrounding meta-atoms in the time domain. We employed various types of metaatom structures and were able to detect minute changes in the concentration of trace amounts of ethanol and glucose water solutions by monitoring the shift in the resonance frequencies. This technique contributes compactification of the THzmicrofluidic chip with high sensitivity and accelerates the developments of future microfluidics integrated with THz technology, such as lab-on-a-chip devices and THz micro total analysis systems.
KEYWORDS: Terahertz radiation, Microfluidics, Liquids, Transmittance, Near field, Near field optics, Minerals, Frequency conversion, Chemical analysis, Imaging spectroscopy, Terahertz metamaterials, Nonlinear crystals
We present a nonlinear optical crystal-based terahertz (THz)-microfluidic chip with a few arrays of asymmetric metaatoms, elementary units of metamaterials, for the measurements of trace amount of liquid solutions. A near-field THz emission source that is locally generated in the process of optical rectification at the irradiation spots of fs laser beams induces a sharp Fano resonance and modifies the resonance frequency of the meta-atoms when the channel is filled with solutions with different concentrations. Using this chip, we successfully detected minute changes in the concentration of trace amounts of ion solutions by monitoring the shift in the resonance frequency. The detectable sensitivity of attomole order of solute in a less than 100 pL volume of the solution was achieved.
Single human hairs using a scanning laser terahertz (THz) imaging system are evaluated. The system features near-field THz emission and far-field THz detection. A sample is set in the vicinity of a two-dimensional THz emitter, and an excitation laser beam is scanned over the emitter via a galvanometer. By detecting the transmitted THz wave pulses that are locally generated at the irradiation spots of the excitation laser, we can obtain the THz transmission image and the spectrum of the sample with imaging time of 47 s for 512×512 pixels and maximum resolution of ∼27 μm . Using the system, we succeeded in observing the specific features of single human hairs in both the THz transmittance spectra and transmission images; it was found that the THz transmittance spectrum of gray hair shows a tendency of increase while that of black hair shows a decrease with increasing frequency above 1.2 THz. We could also observe the change of the moisture retention in the hair, and it is found that cuticles play one of the important roles in keeping moisture inside the hair. Those obtained data indicate that our system can be useful for evaluating single human hairs and those kinds of microscale samples.
We examine InP and InGaAs Schottky type photoconductive antenna for the THz generation excited by femtosecond
laser(fs) at a wavelength of 1560nm. Since InP has an energy gap of 1.3 eV, which is much larger
than photon energy of fs laser. We obtained THz wave generation from both PC antennas with sufficient THz
amplitude, which is comparative to that of low temperature grown GaAs.We also developed new type of InGaAs
PC antennas which includes insulating gap in a PC structure.Highly bright THz beam was generated from the
InGaAs PC antennas.
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