united nation, educational, scientific and cultural organization the ab<ius i International centre for theoretical physics international atomic energy agency SMR 132-1 WINTER SCHOOL ON LASER SPECTROSCOPY AND APPLICATIONS 19 February - 2 March 21 Characterization of visible, UV and NIR femtosecond pulses Lecture II E. RIEDLE Ludwig-Maximilians-Universitaet Munich Lehrstuhl fuer Biomolekular Optik - Sektion Physik Munich, Germany These are preliminary lecture notes, intended only for distribution to participants. strada costiera, II - 3414 trieste italy - tel. +39 42241 I I fax +39 4224163 - 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 21) E. Riedle Powermeter for Femtosecond Pulses??? Wavelength Ranges of SmartSensors 1 nm 1, m* \ Thermal Sensors 25 nrn 19 mi 19 nm BBHH 25nm Semiconductor Sensors 4 ran 4 nm OOnm Pyroelectrlc Sensors 19 nm! 1.64 nm 1,55nm 3,5 nm 1. nm 1, nm 1,6 nm 6, nm unit i
7 1 Grating Efficiency Curves a / s i g / ", / J I / \ 3 Unttftnm Qradngs s 12 Untsftnm OraUnot 6 UrmMm OraUnot i s g. \ f» \ 1: \ 24 UntsAnm OraHnos 36 UnMMm Gratings I: A 'Si : A
o g CD o 3 O" Autocorrelation Measurements Correlation function: oe = J The shape of a sample pulse is measured by observing the overlap with a shorter reference 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) <p(t) co slowly varying envelope of the electric field slowly varying phase carrier frequency of laser By suitable experimental observation all fast variations of the field and all spatial dependencies are averaged. Only the terms pertaining to 5(t) are recorded.
c o 1-2 g 1-H o oo 1-2 4 A Fundamental 4 4 / sech 2 fit % T =25.6 fs? -1-5 5 1 Delay Time (fs) 7 75 8 Wavelength (nm) AvAt =.47 25 fs Second Harmonic Generation Autocorrelation measurement of ultrashort pulses Filter PMT dichroic mirror 1 4 c o fio-h 8 ( CO 2 1-2 J Gauss Fit '; i FWHM=47fs' 36 38 4 Wavelength (nm) -1-5 5 1 Delay Time (fs) 25 fs AvAt =.55 delay time
In a Michelson interferometer (with second harmonic detection) there is no complete averaging and the phase of the electric field has be taken into account: A AQinterferometric( x ) ~ J dt Re A(x) = J dtj^t-x) + g*(\) + 4 2(t-x)5 (t)l "background" + "envelope" B(x)= Jdt "fringes" C(x)= jdt "higher order terms" interferometric autocorrelation / fringe resolved 1 fs pulses at 63 nm AX = 63 nm AvAx =.5-4 -2 2 4 delay time (fs)
Pulse Characterization by Photodiodes AIGaAs LED: quadratic dependence at 8 nm, AC of 8 fs-pulses D. T. Reid, M. Padgett, C. McGowan, W. E. Sleat, and W. Sibbett, Opt. Lett. 22, 233 (1997) GaAsP photodiode: quadratic dependence at 8 nm, AC of 6 fs-pulses J. 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 9 and 48 fs-pulses T. 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 IFAC, CC: UG5
Autocorrelation Traces at 51 nm Unchirped Pulses I Counter Chirped Pulses 1 nm BBO 1p.m BBO SiC: T = 15.1 fs BBO: T = 14.7fs CC: 24 fs CC: 26 fs -6-3 3 6-6 -3 3 6 25 nm BBO CC: 29 fs 25 nm BBO CC: 52 fs i i i i i I i i i i 1 i i i i I i i i i I 48 51 54 nm SiC-Diode CC: 28 fs SiC-Diode CC: 62 fs 2 delay time (fs) -1-5 5 1-1 -5 5 1 delay time (fs) delay time (fs)
2 * i experiment 8 -" simulation & eo-- 6 4 o 2 - HBBO SiC - 25 nm 1 xm - iii 11 no chirp red pulse chirped pulses counter chirped _ SiC BBO BBO 25}im 1 im SiC BBO 25 nm BBO 1 urn" Gaussian pulses: At = 18fs Chirp: 1.9fs/THzat6nm -2.1fs/THzat5nm * A. M. Weiner, IEEE J. Quantum Electron. 19,1276 (1983), SVA-appr. Frequency Resolved Sum Frequency Signal no chirp red pulse chirped pulses parallel chirped pulses counter chirped no phase matching phase matching in 1 nm BBO 114 112 g 11 b 18 % 16 ^ 114 3 112 11 18 16-8-4 4 8-8-4 4 8-8-4 4 8-8-4 4 8 delay time x (fs)
Conclusions Bandwidth limitation of 1 xm nonlinear crystals can result in observed crosscorrelations much shorter than the real ones Reliable and simple auto- and crosscorrelation measurements of sub-2 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: comparison between nonlinear crystals and SiC photodiodes Opt. Commun. 184,321-328 (2) Frequency Resolved Optical Gating Schematic setup for Kerr (polarization) FROG BS PI 11 Kerr, L1 9 medium L2 Monochromator 1 I 2 Peter Dietrich Delay line FROG signal
FREQUENCY-RESOLVED OPTICAL GATING (FROG) 3.Q J ncl/ Ise lengtf Transform-Limited = No Chirp 2.- 1.5-1.-.5-.- -.5- -1.- -1.5- -7.5-5.-2.5. 2.5 5. 7.5 Time Delay (pulse lengths) 123-1 -6 «-4 4 6 8 1 12 K.W. DeLong, DJ. Kane, R. Trebino (Sandia National Laboratories, Livermore,CA) ) ) CO a CO CO (pea) esaqd (PBJ) 9SBt d Linear Chirp = Quadratic Phase a Q i -7.5-5. -2.5. 2.5 5. 7.5 12-1 -6-6 -4-2 2 4 6 8 1 12 CO O Spectral Quartic Phase ) o J3 C(D 3 O -7.5-5.-2.5. 2.5 5. 7.5.8".6".4" 1.- 2- Mamity - - Phaas A / n / \ f J 4-2 Time 2-25 -2-15 -1-5 < (OIU) L }6ue 9ABM
Characterisation of Laser Pulses with SPIDER (Spectral Phase Interferometry for Direct Electric-Field Reconstruction) Principle Experimental Setup Results Conclusion Intensity (counts) Length a. t Delay CO I( 1 C 5
p o o13 C/)" CL > Imsle O a tt. IO CO 1998 II ^ x f f s S i m - nil O" *T1 JLI (D a Rec tio w73 O ctr SL "D IT fi> ( D' erfei 3 a o 1 "HI CD r Spectral Shearing Interferometry Spectrum 1 Spectrum 2 Interference Spectral Shear Q, 15-1- 5- - 97 98 99 1 11 Frequency (THz) 12 13
Window Frequency Fourier transform / S Time i Select temporal sideband Frequency i Unwrap phase - Subtract calibration - Concatenate Retrieve argument of inverse Fourier transform.l Time CO 15 a> o CL X LU Fourier transform Frequency Time
Spectral Phase of NOPA after Chirped Mirror - -5- Reflexes 18 Reflexes 4 Reflexes g -1- -15- -2- -25-98 99 1 11 Frequency (THz) 12 13 Pulse Shape of NOPA after Chirped Mirror -1. -.8 -.6 -.4 Time (a.u.).