Single-shot characterization of sub-15fs pulses with 50dB dynamic range

1. Single-shot characterization of sub-15fs pulses with 50dB dynamic range A. Moulet1 , S.Grabielle1, N.Forget1, C.Cornaggia2, O.Gobert2 and T.Oksenhendler1 1FASTLITE, Centre scientifique d’Orsay Bât.503, Orsay, France2DSM/IRAMIS/SPAM/ATTO, CEA Saclay, Saclay, France forget@fastlite.com

2. Self-Referenced Spectral Interferometry Time-dependent intensity dynamic range of ~50dB Measurement of coherent contrast • SRSI is a recently demonstrated self-referenced pulse measurement technique with unique properties: • single-shot (spectrum and phase are measured) • achromatic (third order, degenerate NL effect) • collinear (no beam splitting, totally collinear) • compact footprint (A5) • accurate: no calibration step, analytical “Self-referenced spectral interferometry”, T.Oksenhendler et al., APB 99, p1-6 (2010),

3. Spectral interferometry I(w) w Spectral interference pattern: I(t) Two delayed pulses: Pulse 1 Pulse 2 t

4. Spectral interferometry DC term AC term Quadratic equation if • Both pulses are completely characterized if one spectral phase is known. A reference pulse is needed, with: • flat phase • broader spectrum

5. Creation of a reference pulse ? I(w) f(w) I(t) w t Modulated spectrum Spectral phase Broader spectrum Flatter phase Broader spectrum Flatter phase XPW I(w) f(w) I(t) XPW can be used as reference pulse Input pulse XPW pulse XPW active media w t Spectral domain before XPW Spectral domain After XPW Time domain

6. SRSI experimental setup Reference (XPW) pulse Input pulse replica Replica generation XPW filtering Main pulse extinction Spectrometer Birefringent plate BaF2,1mm Polarizer Polarizer “Self-referenced spectral interferometry”, T.Oksenhendler et al., APB 99, p1-6 (2010), Polarizer Iris Iris Focusingmirror XPW crystal Polarizer Calcite plate 110mm Spectrometer Focusingmirror 260mm

7. Experimental results F.T-1 DC AC Input spectral amplitude and phase reconstruction Consistency check with the XPW spectrum enlargement and cleaning CEA laser and hollow core fiber: 810nm, 160nm, 10J, 1kHz

8. Experimental results: cross-check with SPIDER ≈12 fs Feedback Amplified Ti:Sa laser Hollow-core fiber (Ar, 2 bar) Dazzler SRSI SPIDER -210fs2 were added by Dazzler to compensate for the dispersion of the optics of the SRSI device

9. Dynamic range – spectral domain Spectral amplitude ( intensity) is measured on a broader spectral support than that of the pulse’s. Spectral range of validity of the measurement (~200nm) XPW Input Dynamic range of spectrometer ~25dB Dynamic range of the measurement >50dB

10. Dynamic range – time domain Another day, another pulse duration… Pulse duration FWHM = 14.5fs FTL FWHM = 14.6fs Measured I(t) FTL I(t) Artifacts ?

11. Dynamic range – time domain For a measurement limited by shot-noise, the expected time dynamic range is: =52dB Number of illuminated pixels (~512) SNR of the CCD detector (~25dB) Measured I(t) Effect of residual spectral phase FTL I(t) Expected dynamic range

12. Dynamic range – time domain To check the validity of the phase measurement and assess the dynamic time range: compensation of residual phase oscillations with the pulse shaper: Before feedback After feedback Expected dynamic range t=14.6fs t=14.6fs s=34.6fs s=19.3fs sFTL=18.6fs

13. Conclusions and prospects Sub-15fs pulses were characterized by SRSI and results were cross-checked with SPIDER measurements Assessed time dynamic range over ±400fs: 50dB Std. dev. is more relevant than FWHM pulse duration for fine compression: high order phase reallymatters • Using spectrometers with cooled multiline CCD detectors, single-shot characterization with dynamic ranges as large as 85 dB on a picosecond scales could be reached.

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16. Taking residual XPW phase into account: iterative algorithm Interferogram Spectrum + Spectral phase approximation Spectral complex amplitude Phase difference FT First approximation: XPW phase Time complex amplitude Hope:

17. Spectrum discrepancy

18. Fourier Transform treatment - 1 I(w) w I(t) F.T-1  t +t - t 0 Numerical filter, centering I(t)  I(w) j(w) F.T  t w 0 +t C.Froehly, A.Lacourt, J.C.Vienot: J. Opt. (Paris) 4, 183 (1973) L.Lepetit, G.Chériaux, M.Joffre: J. Opt. Soc. Am. B 12, 2467 (1995)

19. Fourier Transform treatment - 2 I(w) w I(t) F.T-1  t +t - t 0 Numerical filter I(t)  I(w) F.T  t w 0 C.Froehly, A.Lacourt, J.C.Vienot: J. Opt. (Paris) 4, 183 (1973) L.Lepetit, G.Chériaux, M.Joffre: J. Opt. Soc. Am. B 12, 2467 (1995)

20. Limitations ? Spectrometer bandwidth Dispersion of crystals ~160nm FWHM Resolution of the spectrometer Birefringent delay ~±400fs FWHM Spectral broadening is required Extinction ratio of polarizers Dynamic of the spectrometer • Bandwidth: • Time range: • Pulse complexity: • Dynamic range: (spectral resolution)

21. SRSI properties • achromatic: the XPW effect is automatically phase-matched (collinear and degenerated 3nd order NL effect) • single beam: no beam splitting, totally collinear • single shot: spectrum and phase are measured for the same interferogram • accurate: analytical, no calibration/integration step • but… requires XPW broadening required Large chirps must be removed before measurement Retrieval error with a gaussian pulse (FWHM = 20 nm) Error (%) <10%

22. Experimental results with a Ti:S amplified laser 800nm, 40nm, 2mJ, 100Hz F.T-1  Numerical filter, centering, FT 

23. Spectrum reconstruction accuracy Measured spectrum (dashed red) and reconstructed spectrum with SRSI calculation (blue)