DazScope
manual
Chapter 5 : Theory
Added second order (fs
2
)
S
H
G
s
pe
ct
ru
m
(
nm
)
-3000 -2000 -1000
0
1000
2000
3000
380
385
390
395
400
405
410
415
420
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Fourier-transform limited
Added second order (fs
2
)
S
H
G
s
pe
ct
ru
m
(
nm
)
-3000 -2000 -1000
0
1000
2000
3000
380
385
390
395
400
405
410
415
420
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Fourier-transform limited
Figure 5.2: Chirp scan - Fourier transform limited case. White dots: second order derivative of
the spectral phase as a function of wavelength.
•
one with a pure third order only +50 000fs
3
•
one with a pure fourth order only +2 000 000fs
4
•
one with a sinusoidal spectral phase (
For the first example of distorted pulse, a purely chirped pulse, the compensation of the spectral
phase occurs for the same chirp value at every wavelength. So compared to the Fourier transform
limited pulse, on the SHG spectra vs chirp image, it only shifts the image laterally. The value
of the shift corresponds directly to the chirp. For the purely third order spectral phase pulse,
as the local chirp in a 3rd order is linear, the image corresponds to a linear chirp optimization
vs wavelength. For a more complex phase, the image is distorted but still corresponds for each
wavelength to the chirp value that flatten the phase at this wavelength. The image looks like the
second order phase value vs wavelength:
•
2nd order: lateral shift,
•
3rd order: linear spread,
•
4th order: horse shoe. . .
As for FROG the map image gives a good qualitative information about the phase. The quan-
titative value of the phase (more precisely of the second order derivative of the spectral phase)
is determined by the estimation for each wavelength of the center of symmetry as the first order
momentum:
The determination by the center of symmetry is robust to noise and requires very few points
(11 points per scan is enough for optimization process). It is especially efficient on the wings of
FASTLITE-9 september 2008
