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Ultrabroadband terahertz generation using DAST single crystal

Ultrabroadband terahertz generation using DAST single crystal. APPLIED PHYSICS LETTERS 97, 021105-1 I.Katayama, R.Akai, M.Bito, H.Shimosato, K.Miyamoto, H,Ito and M.Ashida. Ashida lab. Takuya Iwasa. Contents. Introduction Motivation Experimental setup Results & discussion Summary

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Ultrabroadband terahertz generation using DAST single crystal

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  1. Ultrabroadband terahertz generation using DAST single crystal APPLIED PHYSICS LETTERS 97, 021105-1 I.Katayama, R.Akai, M.Bito, H.Shimosato, K.Miyamoto, H,Ito and M.Ashida Ashida lab. Takuya Iwasa

  2. Contents • Introduction • Motivation • Experimental setup • Results & discussion • Summary • My work

  3. E THz wave t Probe laser t Time delay THz Spectroscopy SystemTime Domain Spectroscopy（THz-TDS） • THz-TDS uses short pulses of broadband THz radiation. • The transmitted THz electric field is measured coherently, which provides both high sensitivity and time-resolved phase information. THz-TDS pump probe system Principle of THz-TDS

  4. Electromagnetic wave Wavelength • THz radiation is from 1011 to 1013Hz approximately. • If we generate broader radiation, we can measure from THz region to optical region in continuity. 30mm 3mm 300μm 30μm 3μm 300nm Far infrared Submilimeter wave Near infrared Micro wave optical 10GHz 0.1THz 1THz 10THz 100THz 1PHz Frequency broader THzregion

  5. A 400-μm-thick DAST crystal was used as nonlinear crystal. A DAST crystal is an organic compound crystal and has large nonlinear optical coefficient.(非線形光学係数） THz emitter Difference frequency generation Nonlinear crystal THz wave fs laser Fourier transform Intensity Intensity ω2 ω1 ω３ frequency frequency DAST crystal

  6. THz detector Photoconductive antenna Current meter A μ: mobility of electron N: the number of carrier fs laser THz wave

  7. Motivation • To generate the terahertz wave using a DAST crystal by considering the refractive index dispersion. • To detect the THz wave generated by aDAST crystal using monochromator and THz-TDS.

  8. Experimental setup (Spectral Phase Interferometry for Direct Electric-field Reconstruction)

  9. BaF2(a positive dispersion medium) pulse image Positive chirping Short wavelength Positive dispersion medium Long wavelength Time lag Group velocity dispersion (郡速度分散)

  10. Results & discussion The data of laser phase spectra observed using SPIDER. BaF2 thickness ―0mm ―2mm ―4mm 0mm-thick BaF2 2mm-thick BaF2 0mm-thick BaF2 Long wavelength Short wavelength Negative chirping Positive chirping

  11. Results & discussion BaF2 thickness ―0mm ―2mm ―4mm The best of these data is the one of negative chirping.

  12. Experimental setup Chirp mirror Ti:Sapphire laser BS Chopper Pump pulse BaF2 plate DAST 400mm Delay stage Band-pass filter PC antenna Probe pulse I/V amp lock-in amp PC

  13. Results & discussion In this graph, very high frequency part is present.

  14. Results & discussion BaF2 thickness ―0mm ―2mm ―4mm The Fourier transform of the electric waveform. (dotted line)

  15. Results & discussion 0mm-thick BaF2 2mm-thick BaF2 DAST (Large positivedispersion) Short wavelength Short wavelength Long wavelength Long wavelength The region of generating High-frequency THz wave The energy is absorbed a lot.

  16. Summary • In the DAST crystal, the group velocity dispersion is important for the generation of the ultrahigh-frequency terahertz wave. • A waveform is detected by using photoconductive antenna.

  17. My work I try to measure a wave form by using this optical system when there is a sample in front of PC antenna.

  18. Monochromator Concave mirror Diffraction grating Slit Slit HgCdTe and InAs Detector THz pulse

  19. I (t) W w (t) SPIDER法 (Spectral Phase Interferometry for Direct Electric-field Reconstruction) Sum frequency W I (w) w Intense strongly-chirped pulse from Ti: sapphire amplifier Nonlinear Crystal t I (t) Interferogram Replica2 Replica1 I (w) Pulse to be measured and its duplication SPIDER interferogram w

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