Interferometric autocorrelation Optical autocorrelation

setup interferometric autocorrelator, similar field autocorrelator above, following optics added: l: converging lens, shg: second-harmonic generation crystal, f: spectral filter block fundamental wavelength.

as combination of both previous cases, nonlinear crystal can used generate second harmonic @ output of michelson interferometer, in collinear geometry. in case, signal recorded slow detector is

i

m


(
τ
)
=

∫

−
∞


+
∞



|

(
e
(
t
)
+
e
(
t
−
τ
)

)

2




|


2


d
t


{\displaystyle i_{m}(\tau )=\int _{-\infty }^{+\infty }|(e(t)+e(t-\tau ))^{2}|^{2}dt}

i

m


(
τ
)


{\displaystyle i_{m}(\tau )}

called interferometric autocorrelation. contains information phase of pulse: fringes in autocorrelation trace wash out spectral phase becomes more complex.

two ultrashort pulses (a) , (b) respective interferometric autocorrelation (c) , (d). because of phase present in pulse (b) due instantaneous frequency sweep (chirp), fringes of autocorrelation trace (d) wash out in wings. note ratio 8:1 (peak wings), characteristic of interferometric autocorrelation traces.