united nation, ab<IUSeducational, scientific

and culturalorganization

theiInternational centre for theoretical physics

international atomicenergy agency

SMR 1302- 10

WINTER SCHOOL ON LASER SPECTROSCOPY AND APPLICATIONS

19 February - 2 March 2001

Characterization of visible, UV and NIRfemtosecond pulses

Lecture II

E. RIEDLELudwig-Maximilians-Universitaet Munich

Lehrstuhl fuer Biomolekular Optik - Sektion PhysikMunich, Germany

These are preliminary lecture notes, intended only for distribution to participants.

strada costiera, II - 34014 trieste italy - tel. +39 04022401 I I fax +39 040224163 - scijnfo@ictp.trieste.it - www.ictp.trieste.it

Characterization of visible, UV and NIR femtosecond pulses

- pulse energy

- spectral distribution

- beam profile

- intensity autocorrelation

- fringe resolved autocorrelation

- crosscorrelation

- FROG: frequency resolved optical gating

- SPIDER: spectral phase interferometry for direct electric-field reconstruction

- concluding remarks

WINTER SCHOOL ON LASER SPECTROSCOPY AND APPUCATIONS (19 February - 2 March 2001) E. Riedle

Powermeter for Femtosecond Pulses ???

Wavelength Ranges of SmartSensors

100 nm 1,000 m*\

10.000 nm 100,000 nm

Thermal Sensors250 nrn • • • • •

190 mi • • • • •190 nm BBHH

10,600 nm

6,000 nm

250 nm • • • • • • • • • •Semiconductor Sensors

400 nm

3,500 nm

400 ran0OOnm

Pyroelectrlc Sensors190 nm!

1.064 nm1,550nm

unit i

a

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i

7

s § § g

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§

§

g

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Grating Efficiency Curves

300 Unttftnm Qradngs

„ /" J, /I /

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1200 Untsftnm OraUnot

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Autocorrelation Measurements

Correlation function:oe

= JThe shape of a sample pulse is measured by observing the overlap with a shorterreference pulse at variable delay. A nonlinear detector records the signal.

Such a reference pulse is often not available and the sample pulse itself is used.

Intensity AC:oo

A AC(x) = J - x)dt

Pulse:

5(t) slowly varying envelope of the electric field

<p(t) slowly varying phase

co| carrier frequency of laser

By suitable experimental observation all fast variations of the field and all spatialdependencies are averaged. Only the terms pertaining to 5(t) are recorded.

Fundamental

100-

co

2 10-Hgooo

10-2 4

A44

/• sech2fit %

£ T =25.6 fs ?•

-100 -50 0 50 100

Delay Time (fs)

700 750 800Wavelength (nm)

AvAt = 0.47

25 fs Second Harmonic Generation

100 4

co

fio-H8(0CO

2 10-2

J Gauss Fit ';

i FWHM=47fs'

-100 -50 0 50 100

Delay Time (fs)

360 380 400

Wavelength (nm)

25 fs

AvAt = 0.55

Autocorrelation measurementof ultrashort pulses

PMT

Filter

dichroicmirror

delay time

In a Michelson interferometer (with second harmonic detection) there is nocomplete averaging and the phase of the electric field has be taken into account:

AAQinterferometric(x) ~ J dt

R e

A(x) = J d t j ^ t - x ) + g*(\) + 4£2(t-x)5|(t)l "background" + "envelope"

B(x)= Jdt

C(x)= j d t

"fringes"

"higher order terms"

interferometric autocorrelation / fringe resolved

10 fs pulses at 630 nm

AX = 63 nmAvAx = 0.5

-40 -20 0 20 40delay time (fs)

Pulse Characterization by Photodiodes

AIGaAs LED: quadratic dependence at 800 nm, AC of 80 fs-pulsesD. T. Reid, M. Padgett, C. McGowan, W. E. Sleat, and W. Sibbett, Opt. Lett. 22, 233 (1997)

GaAsP photodiode: quadratic dependence at 800 nm, AC of 6 fs-pulsesJ. K. Ranka, A. L. Gaeta, A. Baltuska, M. S. Pshenichnikov, D. A. Wiersma, Opt. Lett. 22, 1345 (1997)

SiC photodiode: quadratic dependence at 497 nm, AC of 90 and 480 fs-pulsesT. Feurer, A. Glass, R. Sauerbrey, Appl. Phys. B. 65, 295 (1997)

Advantages :

• no phase matching => no angle tuning, broad acceptance bandwidth

• no polarization dependence

• no photomultiplier needed

• robust and compact

• readily available and inexpensive

Experimental Setup

UG5

IFAC, CC: 0

Autocorrelation Traces at 510 nm

SiC: T = 15.1 fs BBO: T = 14.7fs

-60 -30 0 30 60 -60 -30 0 30 60

480 510 540 nm

00 2 0 delay time (fs)

Unchirped Pulses

100 nm BBO

CC: 24 fs

25 nm BBOCC: 29 fs

SiC-DiodeCC: 28 fs

I

i i i i i I i i i i 1 i i i i I i i i i I

Counter Chirped Pulses

100p.m BBO

CC: 26 fs

25 nm BBOCC: 52 fs

SiC-DiodeCC: 62 fs

-100 -50 0 50 100 -100 -50 0 50 100delay time (fs) delay time (fs)

2 *

80 -

& eo-

6 40o

20 -

• i experiment" • • simulation•-

_ SiC BBO BBO25}im 100 |im

SiC BBO25 nm

• •HBBO

100 |xm

iSiC BBO

25 nm

|

11IIBBO

100 urn"

-

-

Gaussian pulses:

At = 18fs

Chirp:

1.9fs/THzat600nm

-2.1fs/THzat500nm

no chirp red pulse chirped pulses counter chirped

* A. M. Weiner, IEEE J. Quantum Electron. 19,1276 (1983), SVA-appr.

no phase

matching

phase

matching in

100 |nm BBO

Frequency Resolved Sum Frequency Signal

no chirpred pulse

chirped

pulses parallel

chirpedpulses counter

chirped

1140

1120 g1100 b

1080 %

1060 ^

1140 3

1120

1100

1080

1060

-80-40 0 40 80 -80-40 0 40 80 -80-40 0 40 80 -80-40 0 40 80

delay time x (fs)

Conclusions

• Bandwidth limitation of £ 100 |xm nonlinear crystals can result in

observed crosscorrelations much shorter than the real ones

• Reliable and simple auto- and crosscorrelation measurements of

sub-20 fs visible pulses in SiC photodiodes (two-photon conductivity)

• Crosscorrelation at the sample position of the spectroscopic

experiment

S. Lochbrunner, P. Huppmann, and E. Riedle

Crosscorrelation measurements of ultrashort visible pulses: comparisonbetween nonlinear crystals and SiC photodiodes

Opt. Commun. 184,321-328 (2000)

Frequency Resolved Optical GatingSchematic setup for Kerr (polarization) FROG

BS

PI

Delay line

11 Kerr , 9L 1 medium L 2

Mono-chromator

1 I

©2000 Peter Dietrich

FROGsignal

oJ3C(D3O

FREQUENCY-RESOLVED OPTICAL GATING

(FROG)

Transform-Limited = No Chirp

3.Q

J

ncl/

Iselen

gtf

2.00-1.50-1.00-0.50-0.00-

-0.50--1.00--1.50-

-7.5-5.0-2.5 0.0 2.5 5.0 7.5

Time Delay (pulse lengths)

K.W. DeLong,DJ. Kane,R. Trebino

(Sandia NationalLaboratories,

Livermore,CA)•123 -100 -60 • « -40 40 60 80 100 120

Linear Chirp = Quadratic Phase

-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5

•120 -100 -60 -60 -40 -20 0 20 40 60 80 100 120

Spectral Quartic Phase

-7.5-5.0-2.5 0.0 2.5 5.0 7.5

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Characterisation of Laser Pulseswith SPIDER

(Spectral Phase Interferometry for Direct Electric-Field Reconstruction)

• Principle• Experimental Setup• Results• Conclusion

Intensity (counts) Length

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Spectral Shearing Interferometry

Spectrum 1Spectrum 2Interference

150-

100-

— 5 0 -

0-

Spectral Shear Q,

970 980 990 1000 1010

Frequency (THz)

1020 1030

Fouriertransform

Frequency

Frequency

i

Retrieveargument of

inverseFourier

transform

• Unwrap phase- Subtract calibration

- Concatenate

Fouriertransform

Frequency

Window

/

STime

iSelect

temporalsideband

.LTime

Time

CO

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oCLX

LU

Spectral Phase of NOPA after Chirped Mirror

0-

-5 -

g -10-

-15-

-20-

-25-

0 Reflexes18 Reflexes40 Reflexes

980 990 1000 1010Frequency (THz)

1020 1030

Pulse Shape of NOPA after Chirped Mirror

-1.0 -0.8 -0.6 -0.4

Time (a.u.)0.0