Research

Research topics in our laboratory are as follows:

  • Terahertz time-domain spectroscopy (THz-TDS)
    We are using the THz-TDS system to characterize a wide variety of materials such as semiconductors, polymers, ceramics, pharmaceutical and agricultural products. This system can also be used to obtain images of optically opaque materials. In this system, THz waves are generated using photoconductive antennas excited by a femtosecond laser (wavelength = 780nm, pulse width <100fs, power = 20mW).

Figure: THz TDS system

Figure: Transmission mode THz-TDS system

Related works:

  1. H. Ichikawa et al. Opt. Mat. Express, vol. 23, Issue 4, pp. 961-981 (2023)
  2. K. Hashimoto et al. Optics, vol.3, pp. 99-106 (2022)
  3. S. Takagi et al, App. Opt., vol. 59, Issue 3, pp. 841-845 (2020)
  4. P. B. Ishai et al., PCCP. vol. 17, pp. 15428-15434 (2015)
  5. S. R. Tripathi et al, Corr. Sci., vol. 62, pp. 5-10 (2012)
  • THz biomedical applications: Interaction of terahertz waves with human skin
    Since the interaction of terahertz wave with human skin is not yet clearly understood, we are investigating how terahertz wave interacts with skin using attenuated total reflection terahertz time-domain spectroscopy.

Figure: THz-TDS measurement of skin.

Related works:

  1. K. Hashimoto et al. BioMed Opt. Exp. vol. 13, Issue 9, 4572-4582 (2022)
  2. S. R. Tripathi et al. BioMed Opt. Exp. vol. 9, Issue 3, 1301-1308, (2018)
  3. S. R. Tripathi et al, Sci. Rep. vol. 5, No. 9071, pp 1- 7, (2015).
  • THz wave properties manipulation using sub-wavelength metallic helix array

We are using 2D array of 3D metallic helix array to manipulate the polarization properties of terahertz waves. We made low-cost broadband THz wave polarizer and filters using helical springs.

Figure: metallic helix measurements

Related Works:

  1. K. Yamamura et al. IEEE Photonics Technology Letters, vol. 36, pp. 457-460 (2024)
  2. H. Tomita et al. Optics Letters vol. 46, pp. 2232-2235 (2021).
  3. S. R. Tripathi et al. OSA frontiers in Optics + Laser Science (2020)
  4. K. Kinumura et al. IRMMW-THz 2018
  • High power terahertz wave sources

We are developing a THz wave measurement system using non-linear optical crystal excited by high power femtosecond fiber laser (wavelength: 1550nm, pulse width < 70fs, power = 80mW)

Figure: THz wave generation using non-linear (DAST) crystal

Related works:

  1. H. Uchida, K. Kawauchi et al. Scientific Reports, vol. 12, No. 15082, pp. 1-9 (2022)
  2. H. Uchida et al. JIMT, vol. 41, pp. 552-556, (2020)
  3. S. R. Tripathi et al. APEX, vol. 6, pp. 072703-1, (2013).

We are grateful to the following funding agencies for supporting our research: