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Speaker: Tzung Da Jiang Adviser : Dr. Ja -Hon Lin

Chirp characterization analysis in ultrashort pulse using modified spectrum autointerometric correlation (MOSAIC). Speaker: Tzung Da Jiang Adviser : Dr. Ja -Hon Lin . Outline. Introduction Principal of autocorrelation Principal of MOSAIC and simulation program

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Speaker: Tzung Da Jiang Adviser : Dr. Ja -Hon Lin

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  1. Chirp characterization analysis in ultrashort pulse using modified spectrum autointerometric correlation(MOSAIC) Speaker: TzungDa Jiang Adviser : Dr. Ja-Hon Lin

  2. Outline • Introduction • Principal of autocorrelation • Principal of MOSAIC and simulation program • Retrieve phase and intensity by Genetic algorithms • Conclusion

  3. Introduction • In order to know whether the laser pulse is close to transform-limited after the external pulse compression by the tapered fiber and grating pairs, we use MOSAIC to determine the magnitude of chirp by simply Fourier transformation of the two photon absorption IAC. • Because the MOSAIC is easier way to know the chirp and has very high sensitivity compared with standard autocorrelation measurements. • Besides, we use the one and two IAC and GA algorithm to retrieve the phase and amplitude of pulse.

  4. Autocorrelation • Autocorrelation is used to measure pulse width by calculating interval fringe number . • Each interval fringe has 2 phase shift ,so it available to calculate time of interval fringe . • The difference between one-photon absorption and two-photon absorption is the photon number which cause carrier excitation. one-photon energy gap transition. two-photon energy gap transition. Figure of two photon absorption (a) hn<Eg (b) hn>Eg (a) 2hn<Eg (b) 2hn>Eg

  5. One photon absorption • The electric field as • Since the incident pulse is divided into two by the beamsplitter, the optical field that incident into the photodetector can be written in the form • It can observe the current as • The one photon absorption autocorrelation signal as, • Where The device of Michelson interferometer. Figure of two photon absorption

  6. Two photon absorption • The electric field is • Since the incident pulse is divided into two by thebeamsplitter, the optical field that incident into the photodetector can be written in the form • It can observe the current as

  7. Two photon absorption • The two photon absorption signal as, • Where =0.015 =0.0005 =0.00003 Tp=10(fs) Figure of two photon absorption

  8. Pulse style of autocorrelation and parameter • The electric field of Gaussian pulse. • The parameter of pulse is:

  9. Analyze chirp by MOSAIC • Because the MOSAIC is easier way to know the chirp and has very high sensitivity compared with standard autocorrelation measurements, we use MOSAIC by simply Fourier transformation of the two photon absorption IAC. • Analyze chirp by observe height of lower envelope value ,the greater the envelope value ,the greater chirp value. =0.015 =0.0005 =0.00003 Tp=10(fs) =0.015 =0.0005 =0.00003 Tp=10(fs) Figure of MOSAIC trace The envelope of MOSAIC trace

  10. Algorithms of MOSAIC iact=load(‘file’); iacw=abs(fft(iact)); for x=xohmax1-diff:xohmax1+diff mosaicw(x,1)=0; End for x=xshmax1-diff:xshmax1+diff mosaicw(x,1)=mosaicw(x,1)*2; End mosaict=ifft(abs(mosaicw)); xohmax diff xshmax Program:MATLAB

  11. Result and Discuss • =0.015 • =0 • =0.015 •  =0.00003 • =0.015 •  =0.00003 • =0.015 • =0 • =0.045 • =0 • =0.045 • =0 • =0.045 •  =0.00003 • =0.045 •  =0.00003 • =0.15 •  =0.00003 • =0.15 • =0 • =0.15 • =0 • =0.15 •  =0.00003 The envelope of MOSAIC trace Figure of two photon absorption The envelope of MOSAIC trace Figure of two photon absorption

  12. Analyze pulse by Genetic algorithms • Use Genetic algorithms can retrieve phase and intensity of pulse. =0.015 =0.0005 =0.00003 Tp=10(fs) = -0.00127 =-3.15  10 =1.08  10 Tp=9.45(fs) -5 -5 Figure of two photon absorption Retrieved intensity and phase Figure of error rate

  13. Conclusion • In this work, we analysis the chirp of ultrashort pulses from the MOSAIC trace by the Fourier transformation of the IAC. • From the MOSAIC trace, the chirp of compressed pulses of Ti:sapphire laser after the tapered fiber and the grating pairs can be easily determined. • Besides, the value of chirp parameter can be obtained by the genetic algorithm with one photon absorption and two photon absorption IACs.

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