1. M.Hangyo,M.Tani,and T.Nagashima TERAHERTZ TIME-DOMAIN SPECTROSCOPY OF SOLIDS: A REVIEW International Journal of Infrared and Millimeter Waves,Vol. 26, No. 12,December 2005. p.1661 Ashida Lab. Onishi Yohei

2. Contents Terahertz region Terahertz time-domain spectroscopy Semiconductor Derivation of complex refractive index Biomolecule Application to security Superconductor(my research) Summary

3. Terahertz region frequency region between 0.1 and 10THz Includes information on a lot of physical properties of materials 0.1THz1THz10THz100THz1PHz THz region 0.1 ～ 10THz 3mm 300  m30  m3m3m 300nm Wavelength Frequency FIRMIRNIR 4.1meV

4. Terahertz time-domain spectroscopy (THz-TDS) enables us to observe a waveform ”E(t)” directly Information on both amplitude and phase are directly obtained. Pump beam Delay stage Probe beam THz-TDS fs pulse laser THz emitter THz detector sample

5. Terahertz time-domain spectroscopy (THz-TDS) Figure shows wave form and power spectrum of THz wave. Fourier transformation

6. Application of THz-TDS to solids various kinds of low energy excitations in various materials

7. Semiconductor(Si) Peak delay Amplitude decrease Amplitude increase 100K Figure shows the temperature dependence of the wave form transmitted through the sample.

8. Derivation of complex refractive index d Sample Transmission Fresnel constants Complex transmittance Complex refractive index Fourier transformed spectrum phase modulation change of amplitude (absorption)

9. Semiconductor(Si)

10. Semiconductors(Si) The real and imaginary parts of the complex conductivity fit to Drude model. Drude model THz-TDS is very effective to characterize the electrical properties of semiconductors without electrical contact. N:density of carriers :scattering time of carriers :effective mass of carriers The temperature dependence of the carrier density and mobility is obtained. carrier mobility

11. Biomolecules Biomolecules have relatively sharp spectral lines in THz region. Alanine has optical isomers, D and L. Figure shows the spectra of D-,L-,and 1:1 mixture of D and L alanine. The enantiomer D(L) and racemic compound show quit different spectra with each other.

12. Biomolecules minimum maximum THz spectra can determine the compositional ratio of D-and L-alanine in a mixture. THz-TDS is a new method of the chemical analysis for molecules. measure the THz spectra for various composition ratios Figure shows the dependence of the absorbance of the 74 and 41.5 bands.

13. Application to security penetrates papers, plastics, ceramics, woods, and so on useful to probe unknown materials concealed in containers made of these materials It is possible detect plastic bombs in mails by the THz- TDS THz wave

14. Application to security Figure shows the refractive index and absorption spectra of a plastic bomb called C-4. The most prominent peak signature of C-4

15. Application to security Figure 18 shows the absorption spectra of a C-4 pellet concealed in an envelope. The most prominent peak(27.3 ) signature of C-4

16. Superconductors(my research) Tc ＝ 28K Fourier transformed spectra of a 50nm thin film MgB 2 on the Sapphire at 11-40K I would like to observe the higher superconducting energy gaps highest critical temperature (Tc) of 39K among conventional metal-based superconductors. two superconducting gaps The higher energy gap is not observed by THz-TDS. MgB 2

17. Summary THz-TDS is very effective to study properties of semiconductors, superconductors, and biomolecule. THz spectroscopy become one of the most exciting fields in the basic science and technology, and also expected to be useful in industries.