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Characterization of short pulses.

A. Yartsev

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What is good to know about short pulses?

• Energy of each pulse• Average power• Spectrum• Spatial distribution• Temporal profile

– Satellites– Duration– Shape

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Energy/Power measurements. from pico-Joule to peta-Watt

• Physics of detection

• Choice of detector

• Linearity

• Sensitivity

• Spectral response

• Response time

• Damage

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Spectral shape

• What do you need the spectrum for?• Sensitivity range.• Calibration of the spectrometer.• Dynamic range.• Optics on the way.• Fibber ”wave guides”.

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Beam profile

• Assume Gaussian?– Measure power through calibrated pinholes– Blade-edge method

• Measure real profile.– 2-D detector: CCD matrix– 1-D array detector– Linearity of response

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Temporal profile:What for?

• Satellites: quality of amplification, quality of measurements

• Pulse duration: FWHM• Instrumental response function• Transform-limited pulse• Pulses of random shape

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Electrical (direct) measurements of pulse duration:

not fast enough and (very) expensive.

• Photodiode: >10 ps (+fast Oscilloscope)• Streak Camera: 100 fs (?), ~1 ps

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All-optical methods

• Time from distance: 1 fs 0.3 m• Math: correlation function

– determines F(t) if G() is measured and F’(t) is known.

( ) '( ) ( )G F t F t dt

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Autocorrelation

• Interferometric AC• Intensity AC• Single – shot AC

• Both F(t) and F’(t) are replica’s of the same function E(t)exp

( ) '( ) ( )G F t F t dt

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Interferometric AC• F(t) = E(t)exc[it+i(t)]

• I1() = |E(t)exc[it+i(t)] +E(t-)exc[i(t- )+i(t-)]|2dt

• I2() = |{E(t)exc[it+i(t)] +E(t-)exc[i(t- )+i(t-)]}2|2dt

• First order AC: I1(=0)/I1() = 2• Second order AC: I2(=0)/I2() = 8

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Interferometric AC

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Interferometric AC

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Limitions of AC

• Non-specific: one has assume a particular pulse shape.

• Returns only amplitude.

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Spectrum

Full-field characterization of femtosecond pulses by spectrum

and cross-correlation measurements

OPTICS LETTERS / Vol. 24, No. 23 / December 1, 1999J. W. Nicholson, J. Jasapara, and W. RudolphF. G. Omenetto and A. J. Taylor

( ) '( ) ( )G F t F t dt

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Frequennsy-resolved optical gating

FROG

Rev. Sci. Instrum., Vol. 68, No. 9, September 1997R. Trebino, K. W. DeLong, D. N. Fittinghoff, J. N. Sweetser,

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FROG Rev. Sci. Instrum., Vol. 68, No. 9, September 1997R. Trebino, K. W. DeLong, D. N. Fittinghoff, J. N. Sweetser,

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Single-shot FROG

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FROG

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Limitions of FROG

• Requirements on set-up: linear detector response, step size, S/N.

• Delay-scanning technique.• Measures 2D characteristic – long.• Non-specific: needs a (complicated) retrival

to get pulse. • Does not always converge.

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X-FROG: spectrally-resolved cross-correlation of an unknown pulse with the

reference pulse.

( ) '( ) ( )G F t F t dt

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TADPOLE

Rev. Sci. Instrum., Vol. 68, No. 9, September 1997R. Trebino, K. W. DeLong, D. N. Fittinghoff, J. N. Sweetser,

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FRPP: pump-probe FROG

OPTICS LETTERS / Vol. 27, No. 13 / July 1, 2002S. Yeremenko, A. Baltuˇska, F. de Haan, M. S. Pshenichnikov, D. A. Wiersma

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Self-Referencing Spectral Interferometry for Measuring Ultrashort Optical Pulses

SPIDER

IEEE J Quant.Elctr. Vol. 35, No. 4, April 1999C. Iaconis, I.A. Walmsley

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SPIDER

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Advantages of SPIDER

• No moving parts• Direct reconstruction (>1kHz)• Noise immunity• Low sensitivity to detector spectral response• Precision and consistency mesures from data

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Limitions of SPIDER

• Has to be optimised for a particular time-and spectral range.

• Requires calibration.• Very sensitive to delay between pulses –

sensitive to alignment.

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After SPIDER: ZAP-SPIDER

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After SPIDER: SEA-SPIDER

E. M. Kosik and A. S. Radunsky I. A. Walmsley C. Dorrer OPTICS LETTERS Vol. 30, No. 3, 2005

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After SPIDER: 2DSI

OPTICS LETTERS / Vol. 31, No. 13 / July 1, 2006 J. R. Birge, R. Ell, F. X. Kärtner