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

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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

Time-dependent intensity dynamic range of ~50dB

Measurement of coherent contrast

“Self-referenced spectral interferometry”, T.Oksenhendler et al., APB 99, p1-6 (2010),

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Spectral interferometry

Two delayed pulses:I(t)

Pulse 1

Pulse 2

t

I()

Spectral interference pattern:

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Spectral interferometry

DC term AC term

Quadratic equation

Both pulses are completely characterized if one spectral phase is known. A reference pulse is needed, with:- flat phase- broader spectrum

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Creation of a reference pulse ?

Spectral domain

before XPWTime domain

Spectral domain

After XPW

I(t)

t

I() ()

Modulated spectrum

Spectral phase

I(t)

t

XPW

XPW pulse

Input pulse

XPW active media

Broader spectrum

Flatter phase

I() ()

Broader spectrum

Flatter phase

XPW can be used as reference pulse

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XPW filtering

Spectrometer

Birefringent plate

Polarizer

Replica generation Main pulse extinction

Polarizer

SRSI experimental setup

BaF2,1mm

“Self-referenced spectral interferometry”, T.Oksenhendler et al., APB 99, p1-6 (2010),

110m

m

Spectrometer

260mm

Iris IrisPolarizer

Polarizer

Focusingmirror

XPW crystal

Calcite plate

Focusingmirror

Input pulse replica

Reference (XPW) pulse

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Experimental results

300 350 400 4500

0.2

0.4

0.6

0.8

1

SR

SI S

pectr

um

(u.a

)

Frequency (THz)

Consistency check with the XPW spectrum enlargement and cleaning

300 350 400 4500

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1

Frequency (THz)

Sp

ectr

al in

ten

sity (

u.a

)

Input spectrumXPW spectrum

CEA laser and hollow core fiber: 810nm, 160nm, 10J, 1kHz

340 360 380 400 4200

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Frequency (THz)

Spectr

al in

tensity (

u.a

)

340 360 380 400 420-3

-2

-1

0

1

2

3

Spectr

al phase (

rad)

Input spectralamplitude and phase reconstruction

-1500 -1000 -500 0 500 1000 1500

10-4

10-3

10-2

10-1

100

Time (fs)

Tem

pora

l In

tensity (

u.a

.)

F.T-1

DC AC

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Experimental results: cross-check with SPIDER

-50 -25 0 25 500.0

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1.0

Time (fs)

Tem

pora

l Int

ensi

ty (

u.a.

)

SRSISPIDER

340 360 380 400 4200

0.2

0.4

0.6

0.8

1

Frequency (THz)

Spe

ctra

l int

ensi

ty (

u.a)

340 360 380 400 420-3

-2

-1

0

1

2

3

Spe

ctra

l pha

se (

rad)

SRSI PhaseSPIDER Phase

≈12 fs

Hollow-core fiber (Ar, 2 bar)

Amplified Ti:Sa laser

Dazzler SRSI

SPIDER

Feedback

-210fs2 were added by Dazzler to compensate for the dispersion of the optics of the SRSI device

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300 320 340 360 380 400 420 440 460-80

-70

-60

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-40

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-20

-10

0

10

Frequency (THz)

Nor

mal

ized

spe

ctra

l int

ensi

ty

Dynamic range – spectral domain

Dynamic range of spectrometer

~25dB

Dynamic range of the measurement

>50dB

XPW

Input

Spectral range of validity of the measurement (~200nm)

Spectral amplitude ( intensity) is measured on a broader spectral support than that of the pulse’s.

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Dynamic range – time domain

-400 -200 0 200 400-60

-50

-40

-30

-20

-10

0

Time (fs)

Nor

mal

ized

tim

e in

tens

ity

FWHM=14.51fsFWHM=14.59fs

Measured I(t)

FTL I(t)

Artifacts ?

Pulse duration FWHM = 14.5fs

FTL FWHM = 14.6fs

Another day, another pulse duration…

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-400 -200 0 200 400-60

-50

-40

-30

-20

-10

0

Time (fs)

Nor

mal

ized

tim

e in

tens

ity

FWHM=14.51fsFWHM=14.59fs

Dynamic range – time domain

Number of illuminated pixels (~512)

SNR of the CCD detector (~25dB)

For a measurement limited by shot-noise, the expected time dynamic range is:

=52dB

Expected dynamic range

Effect of residual spectral phase

Measured I(t)

FTL I(t)

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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:

Expected dynamic range

Before feedback

After feedback

=34.6fs =19.3fs

FTL=18.6fs

=14.6fs =14.6fs

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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

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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Our new product

Thank you for you attention

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Spectrum

Taking residual XPW phase into account: iterative algorithm

Interferogram

Spectral complex amplitude

Time complex amplitude

XPW phase

Phase difference+

FT

Spectral phase approximation

First approximation:

Hope:

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340 360 380 400 4200

0.2

0.4

0.6

0.8

1

Frequency (THz)

Spe

ctra

l int

ensi

ty (

u.a)

340 360 380 400 420-3

-2

-1

0

1

2

3

Spe

ctra

l pha

se (

rad)

SRSI PhaseSPIDER Phase

335 345 355 365 375 385 395 405 415 4250.0

0.1

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0.5

0.6

0.7

0.8

0.9

1.0

Frequency (THz)

Spe

ctra

l Am

plitu

de (

a.u.

)

335 345 355 365 375 385 395 405 415 425-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

Spe

ctra

l Pha

se (

rad)

Spectrum discrepancy

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Fourier Transform treatment - 1

I()

F.T

Numerical filter, centering

F.T-1

t0

I(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)

t

I(t)

0

I() ()

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Fourier Transform treatment - 2

I()

F.T-1

0t

I(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)

Numerical filter

t

I(t)

0

F.T

I()

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• Bandwidth:

• Time range:

• Pulse complexity:

• Dynamic range:

Limitations ?

Spectral broadening is required

(spectral resolution)

Spectrometer bandwidth

Dispersion of crystals~160nm FWHM

Birefringent delay

~±400fs FWHM

Resolution of the spectrometer

Extinction ratio of polarizers

Dynamic of the spectrometer

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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

Retrieval error with a gaussian pulse (FWHM = 20 nm)

Err

or

(%)

<10%

Large chirps must be removed before measurement

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Experimental results with a Ti:S amplified laser

F.T-1

Numerical filter, centering, FT

800nm, 40nm, 2mJ, 100Hz

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Spectrum reconstruction accuracy

Measured spectrum (dashed red) and reconstructed spectrum with SRSI calculation (blue)