2019 Fiscal Year Annual Research Report
Novel terahertz waveguide structure: probing low dimensional materials under extremely strong electromagnetic field
| Project/Area Number |
18K13803
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| Research Institution | Shizuoka University |
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Principal Investigator |
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| Project Period (FY) |
2018-04-01 – 2020-03-31
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| Keywords | Terahertz / ultrathin materials / waveguide / spectroscopy / strong field / broadband |
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| Outline of Annual Research Achievements |
This project entitled “Novel terahertz (THz) waveguide structure: probing low dimensional materials under extremely strong electromagnetic field” aims to probe nonlinear THz responses of low dimensional materials including graphene and carbon nanotubes (CNT). The novelty proposed in the project is the use of a parallel plate waveguide (PPWG) structure. The PPWG geometry permits to pump the low dimensional samples under test with an extremely high power THz radiation and subsequently to probe their nonlinear THz responses.
We have measured the linear THz response of unaligned CNT with a standard PPWG and compared the results with those obtained by the conventional THz time domain spectroscopy (TDS). Here, there is a huge difference in the THz absorption of the CNT samples obtained by the two different methods. For unaligned CNT, the THz absorption in the low THz frequency range (0.2-0.5 THz) attained 75% with standard PPWG in the transverse electric mode. In the conventional THz-TDS, the THz absorption is only 20%.
The experimental setup of the project consists initially of only high power THz-TDS but we have extended the THz setup to an ultra-broadband THz spectrometer based on THz air photonics. With this new setup, we have obtained a THz spectrum with bandwidth of 6THz.The signal to noise ratio (S/N) of the THz spectrum is about 200.Currently, we have improved the laser system to generate a pulse duration of 35 fs by optical fiber compression of the original 100 fs laser pulse. The preliminary results indicate a THz spectrum of 10 THz with a S/N around 1000.
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