1. N. Novgorod, IFM, 20.09.2011 Корреляционные методики измерения коротких импульсов терагерцового излучения Alexej Semenov German Aerospace Center

2. Folie 2 Outline  Коррелляция и автокорреляция  Нелинейность и интерференция в автокорреляционных измерениях электромагнитных полей - электрическое поле - интенсивность - Crosstalk  Получение коротких терагерцовых импульсов  Результаты измерений

3. Fluorescent Correlation Spectroscopy Magde, D., Elson, E., and Webb, W.W. (1972) Phys. Rev. Lett. 29, 705

4. Fluorescent Correlation Spectroscopy Autocorrelation function N – average number of the molecules in the focal volume D – diffusion coefficient W x,y WzWz

5. Fluorescent Correlation Spectroscopy Diffusion coefficient

6. Folie 6 Different light - time correlation of photons Thermal sources, gas discharge (natural light) - bunched photons (Bose statistics, strong fluctuation) Lasers (coherent light)- random photons (Poisson distribution, low fluctuation) Single photon sources (fluorescence, quantum dot)- anti-bunched photons

7. Folie 7 Correlation function with a single photon detector Time correlation of photons T koh is the measure for the degree of coherence in thermal light sources C. Zinoni et al., APL 2007

8. Folie 8 Hanbury-Brown/Twiss-Experiment Time correlation of photons Finite response time and/or dead time of a single photon detector brought up the HBT method

9. Folie 9 Outline  Коррелляция и автокорреляция  Нелинейность и интерференция в автокорреляционных измерениях электромагнитных полей - электрическое поле - интенсивность - Crosstalk  Получение коротких терагерцовых импульсов  Результаты измерений

10. Folie 10 Femtosecond pulse lasers Autocorrelator How to measure the pulse duration? SHD – second harmonic generator (non-linear optical crystal) D – any slow detector Interferometric autocorrelation

11. Folie 11 Interferometric autocorrelation Two ultra-short pulses (a) and (b) with their respective interferometric autocorrelation (c) and (d). Because of the phase present in pulse (b) due to an instantaneous frequency sweep (chirp), the fringes of the autocorrelation trace (d) wash out in the wings. Note the ratio 8:1 (peak to the wings), characteristic of interferometric autocorrelation traces. Interferometric autocorrelation

12. Folie 12 Fast optical detectors Interferometer How to measure the response time of the detector? L – femtosecond pulse laser P – polarizer V – slow voltmeter D –detector under study A. Semenov et al., JLTP 1996 Use the nonlinearity V(P) of the detector response and do not forget to eliminate interference P V

13. Folie 13 Intensity autocorrelation Interferometer P. Probst et al., PRB P V YBCO superconducting detector and Ti-Sapphire laser

14. Folie 14 Intensity autocorrelation Two ultra-short pulses (a) and (b) with their respective intensity autocorrelation (c) and (d). Because the intensity autocorrelation ignores the temporal phase of pulse (b) that is due to the instantaneous frequency sweep (chirp), both pulses yield the same intensity autocorrelation. Here, identical Gaussian temporal profiles have been used, resulting in an intensity autocorrelation width twice as long as the original intensities. Note that an intensity autocorrelation has a background that is ideally half as big as the actual signal. The zero in this figure has been shifted to omit this background

15. Folie 15 Fast optical detectors L. Shi et al., APL 1992 Use the mutual current drain of two identical detectors How to measure the linear response time? Crosstalk correlation

16. Folie 16 Crosstalk correlation

17. Folie 17 Outline  Коррелляция и автокорреляция  Нелинейность и интерференция в автокорреляционных измерениях электромагнитных полей - электрическое поле - интенсивность - Crosstalk  Получение коротких терагерцовых импульсов  Результаты измерений

18. THz Synchrotron Radiation Synchrotron radiation

19. Folie 19 Signal appearance J. Feikes et al., PR ST AB 2011 Bending magnet

20. Folie 20 Synchrotron radiation Typical values

21. Folie 21 Coherent synchrotron radiation

22. Coherent THz Radiation from a Synchrotron momentum compaction factor:  p/p  =  L/L  f s 2 reference orbit: L = 240 m LL bunch,  p intensity vs. number of electrons longitudinal bunch length h h  z >  z  intensity vs. number of electrons longitudinal bunch length low alpha optics  z  1 mm  t < 7 ps   10 -4 normal user optics  z > 5 mm  t > 35 ps  = 7·10 -3 h h  z >  z  v  c Single electron 1 ps window THz -pulse 10 ps

23. Folie 23 MLS data sheet Synchrotron

24. Folie 24 Outline  Коррелляция и автокорреляция  Нелинейность и интерференция в автокорреляционных измерениях электромагнитных полей - электрическое поле - интенсивность - Crosstalk  Получение коротких терагерцовых импульсов  Результаты измерений

25. Folie 25 Problems  Radiation pulses in the range 0.1 – 1 THz  Pulse duration 10 – 20 ps  Available detectors Slow – semiconductor bolometers (linear) Fast – superconducting electron bolometers (linear) Fast – superlattice detector (non-linear)  Beam size a few millimeters & detector size a few micrometers

26. Antennensimulation Au-Antenne (100nm) auf Saphir S11=-18 dB bei f = 0,95 THz

27. Antennen + Filter Layout

28. Gesamtstruktur

29. Antennen + Filter S-Parameter im THz-Bereich S11 = S22 = -43 dB bei 0,95 THz S21 = S12 = -32 dB sowie S31 = S32 = -24 dB bei 0,95 THz Signal wird gut in Antenne eingekoppelt und nur wenig reflektiert

30. Folie 30 Martin-Puplett Interferometer Output Input 1 Input 2

31. Typical autocorrelation signal Detector signals seem to overlap over the whole scan length Negative autocorrelation signal Neither the peak at 0 nor the whole response corresponds with the streak camera measurements Period of about 20 ps Peak at zero shorter than the other peaks Beam parameter: 629 MeV, 480 kV, 7.05 kHz, 100mA beam current Streak camera:  FWHM) = 26ps Combination from crosstalk correlation and field correlation

32. Folie 32 Field detector

33. Folie 33 Field autocorrelation Two ultra-short pulses (a) and (b) with their respective field autocorrelation (c) and (d). Note that the autocorrelations are symmetric and peak at zero delay. Note also that unlike pulse (a), pulse (b) exhibits an instantaneous frequency sweep, called chirp, and therefore contains more bandwidth than pulse (a). Therefore, the field autocorrelation (d) is shorter than (c), because the spectrum is the Fourier transform of the field autocorrelation (Wiener-Khinchin theorem).

34. Folie 34 Autocorrelation with superlattice detector S. Winnerl et al., APL 1998 Combination from field and intensity correlation

35. Folie 35 Thank you