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, France
CEA Saclay, Saclay, France
2DSM/IRAMIS/SPAM/ATTO,
forget@fastlite.com
Self-Referenced Spectral Interferometry
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
2010 ICUILConference, Watkins Glen
“Self-referenced spectral interferometry”, T.Oksenhendler et al., APB 99, p1-6 (2010),
Time-dependent intensity dynamic range of ~50dB
Measurement of coherent contrast
Spectral interferometry
I(t)
Two delayed pulses:
Pulse 1
Pulse 2
t
I(w)
Spectral interference pattern:
2010 ICUILConference, Watkins Glen
w
Spectral interferometry
DC term
AC term
Quadratic equation
~
~
if w E1 w   E2 w 
2010 ICUILConference, Watkins Glen
Both pulses are completely characterized if one spectral
phase is known. A reference pulse is needed, with:
- flat phase
- broader spectrum
Creation of a reference pulse ?
Spectral domain
Time domain
before XPW
f(w)
I(w)
I(t)
w
Spectral domain
After XPW
f(w)
I(w)
w
t
Modulated spectrum
XPW
Spectral phase
Broader spectrum
Flatter phase
2010 ICUILConference, Watkins Glen
I(t)
XPW can be used as
reference pulse
Input pulse
XPW active media
XPW
pulse
t
SRSI experimental setup
Replica generation
XPW filtering
Main pulse extinction
Spectrometer
Polarizer Birefringent
plate
BaF2,1mm
Reference (XPW) pulse
Polarizer
Input pulse replica
“Self-referenced spectral interferometry”, T.Oksenhendler et al., APB 99, p1-6 (2010),
Polarizer
Iris
Iris
Focusing
mirror
Calcite plate
Polarizer
Spectrometer
Focusing
mirror
260mm
110mm
2010 ICUILConference, Watkins Glen
XPW crystal
Experimental results
CEA laser and hollow core fiber: 810nm, 160nm, 10J, 1kHz
10
0.8
0.6
F.T-1
0.4
0.2
0
300
350
400
Temporal Intensity (u.a.)
SRSI Spectrum (u.a)
1
450
10
10
10
10
0
-1
-2
-3
-1500
Frequency (THz)
1
0.6
0
0.4
-1
0.2
-2
400
420
Frequency (THz)
Input spectral
amplitude and phase reconstruction
-3
Spectral intensity (u.a)
0.8
380
0
500
1000
1500
Input spectrum
XPW spectrum
2
360
-500
1
Spectral phase (rad)
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Spectral intensity (u.a)
3
340
-1000
AC
Time (fs)
1
0
DC
-4
0.8
0.6
0.4
0.2
0
300
350
400
Frequency (THz)
450
Consistency check with the
XPW spectrum enlargement and cleaning
Experimental results: cross-check with SPIDER
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
3
0.8
1.0
0.9
2
1
0.6
0
0.4
-1
0.2
-2
Temporal Intensity (u.a.)
SRSI Phase
SPIDER Phase
Spectral phase (rad)
2010 ICUILConference, Watkins Glen
Spectral intensity (u.a)
1
0.8
SRSI
SPIDER
≈12 fs
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
340
360
380
400
Frequency (THz)
420
-3
0.0
-50
-25
0
Time (fs)
25
50
Dynamic range – spectral domain
Spectral range of validity of
the measurement (~200nm)
10
XPW
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Normalized spectral intensity
0
Input
-10
-20
-30
Dynamic range
of spectrometer
Dynamic range of
the measurement
-40
~25dB
>50dB
-50
-60
-70
-80
300
320
340
360
380
400
420
440
460
Frequency (THz)
Spectral amplitude ( intensity) is measured on a broader spectral
support than that of the pulse’s.
Dynamic range – time domain
Another day, another pulse duration…
Pulse duration FWHM = 14.5fs
FTL FWHM = 14.6fs
0
Measured I(t)
FWHM=14.51fs
FWHM=14.59fs
2010 ICUILConference, Watkins Glen
Normalized time intensity
-10
-20
FTL I(t)
-30
-40
-50
-60
-400
-200
0
Time (fs)
Artifacts ?
200
400
Dynamic range – time domain
For a measurement limited by shot-noise, the expected time
dynamic range is:
=52dB
Number of illuminated
pixels (~512)
0
Measured I(t)
FWHM=14.51fs
2010 ICUILConference, Watkins Glen
Normalized time intensity
Effect of residual
spectral phase
FWHM=14.59fs
-10
-20
SNR of the CCD
detector (~25dB)
FTL I(t)
-30
-40
Expected dynamic range
-50
-60
-400
-200
0
Time (fs)
200
400
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
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t=14.6fs
t=14.6fs
s=34.6fs
s=19.3fs
sFTL=18.6fs
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 really matters
2010 ICUILConference, Watkins Glen
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.
Our new product
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Thank you for you attention
Taking residual XPW phase into account: iterative algorithm
Spectrum
Interferogram
Phase difference
Spectral phase
approximation
+
Spectral complex
amplitude
FT
First approximation:
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XPW phase
Hope:
Time complex
amplitude
Spectrum discrepancy
3
SRSI Phase
SPIDER Phase
0.8
2
1
0.6
0
0.4
-1
0.2
-2
340
360
380
400
420
-3
1.0
Frequency (THz)
3.0
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Spectral Amplitude (a.u.)
0.9
2.0
0.8
0.7
1.0
0.6
0.5
0.0
0.4
-1.0
0.3
0.2
-2.0
0.1
0.0
-3.0
335 345 355 365 375 385 395 405 415 425
Frequency (THz)
Spectral Phase (rad)
0
Spectral phase (rad)
Spectral intensity (u.a)
1
Fourier Transform treatment - 1
I(t)
I(w)
F.T-1

w
I(w)
j(w)
-t
I(t)
t
0
+t

Numerical filter,
centering
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F.T

w
C.Froehly, A.Lacourt, J.C.Vienot: J. Opt. (Paris) 4, 183 (1973)
0
+t
t
L.Lepetit, G.Chériaux, M.Joffre: J. Opt. Soc. Am. B 12, 2467 (1995)
Fourier Transform treatment - 2
I(t)
I(w)
F.T-1

w
-t
I(t)
I(w)
t
0
+t

Numerical filter
2010 ICUILConference, Watkins Glen
F.T

w
C.Froehly, A.Lacourt, J.C.Vienot: J. Opt. (Paris) 4, 183 (1973)
0
t
L.Lepetit, G.Chériaux, M.Joffre: J. Opt. Soc. Am. B 12, 2467 (1995)
Limitations ?
Spectrometer bandwidth
• Bandwidth:
• Time range:
(spectral resolution)
Dispersion of crystals
~160nm FWHM
Resolution of the spectrometer
Birefringent delay
~±400fs FWHM
• Pulse complexity:
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• Dynamic range:
Spectral broadening is required
Extinction ratio of polarizers
Dynamic of the spectrometer
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
2010 ICUILConference, Watkins Glen
Retrieval error with a gaussian pulse
(FWHM = 20 nm)
<10%
Error (%)
Large chirps must be removed
before measurement
Experimental results with a Ti:S amplified laser
800nm, 40nm, 2mJ, 100Hz
F.T-1

Numerical filter,
centering, FT

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Spectrum reconstruction accuracy
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Measured spectrum (dashed red)
and reconstructed spectrum with SRSI calculation (blue)