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Корреляционные методики измерения коротких импульсов терагерцового излучения Alexej Semenov German Aerospace Center. Outline. Коррелляция и автокорреляция Нелинейность и интерференция в автокорреляционных измерениях электромагнитных полей - электрическое поле - интенсивность - PowerPoint PPT Presentation
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N. Novgorod, IFM, 20.09.2011
Корреляционные методики измерения коротких импульсов терагерцового излучения
Alexej SemenovGerman Aerospace Center
Folie 2
Outline
Коррелляция и автокорреляция
Нелинейность и интерференция в
автокорреляционных измерениях
электромагнитных полей- электрическое поле- интенсивность- Crosstalk
Получение коротких терагерцовых
импульсов
Результаты измерений
Fluorescent Correlation Spectroscopy
Magde, D., Elson, E., and Webb, W.W. (1972) Phys. Rev. Lett. 29, 705
Flu
ore
scen
t C
orr
elat
ion
Sp
ectr
osc
op
y
Autocorrelation function
22,
2
4181
111
)(
)()()(
zyx w
D
w
DNtI
tTtIG
N – average number of the molecules in the focal volumeD – diffusion coefficient
Wx,y
Wz
Flu
ore
scen
t C
orr
elat
ion
Sp
ectr
osc
op
y
Diffusion coefficient
Folie 6
Different light - time correlation of photons
Thermal sources, gas discharge (natural light) - bunched photons (Bose statistics, strong fluctuation)
Lasers (coherent light) - random photons (Poisson distribution, low fluctuation)
Single photon sources (fluorescence, quantum dot) - anti-bunched photons
Folie 7
Correlation function with a single photon detector
Tim
e co
rrel
atio
n o
f p
ho
ton
s
Tkoh is the measure for thedegree of coherence inthermal light sources
C. Zinoni et al., APL 2007
Folie 8
Hanbury-Brown/Twiss-Experiment
Tim
e co
rrel
atio
n o
f p
ho
ton
s
Finite response time and/or dead time of a single photon detector brought upthe HBT method
Folie 9
Outline
Коррелляция и автокорреляция
Нелинейность и интерференция в
автокорреляционных измерениях
электромагнитных полей- электрическое поле- интенсивность- Crosstalk
Получение коротких терагерцовых
импульсов
Результаты измерений
Folie 10
Femtosecond pulse lasers
Autocorrelator
How to measure the pulse duration?
SHD – second harmonic generator(non-linear optical crystal)
D – any slow detector
Interferometric autocorrelation
Folie 11
Interferometric autocorrelation
Two ultra-short pulses (a) and (b) with their respective interferometric autocorrelation (c) and (d). Because of the phase present in pulse (b) due to an instantaneous frequency sweep (chirp), the fringes of the autocorrelation trace (d) wash out in the wings. Note the ratio 8:1 (peak to the wings), characteristic of interferometric autocorrelation traces.In
terf
ero
met
ric
auto
corr
elat
ion
Folie 12
Fast optical detectors
Interferometer
How to measure the response time of the detector?
L – femtosecond pulse laser
P – polarizer
V – slow voltmeter
D –detector under studyA. Semenov et al., JLTP 1996
Use the nonlinearity V(P) of the detectorresponse and do not forget to eliminateinterference
P V
Folie 13
Intensity autocorrelation
Interferometer
P. Probst et al., PRB <2012>
P V
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
-30 -20 -10 0 10 20 30
Delay (ps)
Co
rre
lati
on
sig
na
l (r.
u.)
R1fl
R2fl
GAUSS 7 ps
YBCO superconducting detector and Ti-Sapphire laser
Folie 14
Intensity autocorrelation
Inte
nsi
ty a
uto
corr
elat
ion
Two ultra-short pulses (a) and (b) with their respective intensity autocorrelation (c) and (d). Because the intensity autocorrelation ignores the temporal phase of pulse (b) that is due to the instantaneous frequency sweep (chirp), both pulses yield the same intensity autocorrelation. Here, identical Gaussian temporal profiles have been used, resulting in an intensity autocorrelation width twice as long as the original intensities. Note that an intensity autocorrelation has a background that is ideally half as big as the actual signal. The zero in this figure has been shifted to omit this background
22
2
2
1
2
)(t)E(t)E(aV(t)
IaV(I)
Folie 15
Fast optical detectors
L. Shi et al., APL 1992
Use the mutual current drain of two identicaldetectors
How to measure the linear response time?
Crosstalk correlation
Folie 16
Crosstalk correlation
Cro
ssta
lk c
orre
lati
on
I = const0
I1
R1
I2
R2
(t) (t+ )
021
2211
02,1
)(
),()(
))(1()())(()(
iII
tVRIRI
ItRRtR
tPItIItItR nC
nC
Folie 17
Outline
Коррелляция и автокорреляция
Нелинейность и интерференция в
автокорреляционных измерениях
электромагнитных полей- электрическое поле- интенсивность- Crosstalk
Получение коротких терагерцовых
импульсов
Результаты измерений
THz Synchrotron Radiation
Synchrotronradiation
Folie 19
Signal appearance
J. Feikes et al., PR ST AB 2011
Bending magnet
Folie 20
Synchrotron radiation
Typical valuesfst
ps
e
e
035.0
25
Folie 21
Coherent synchrotron radiation
re(x)
orbit acceptance portion
c
v
25 ps
bunch length ( x) 10 ps
Coherence condition x < l
Coherent THz Radiation from a Synchrotron
momentum compaction factor: p/p = L/L fs
2
reference orbit: L = 240 m
L
bunch, p
intensity vs. number of electronslongitudinal bunch length
h
h
z > l
z l
intensity vs. number of electronslongitudinal bunch length
low alpha optics
z 1 mm
t < 7 ps
10-4
normal user optics
z > 5 mm
t > 35 ps
= 7·10-3
h
h
z > l
z l
v c
Single electron1 ps window
THz -pulse
10 ps
Folie 23
MLS data sheet
Syn
chro
tro
n
Folie 24
Outline
Коррелляция и автокорреляция
Нелинейность и интерференция в
автокорреляционных измерениях
электромагнитных полей- электрическое поле- интенсивность- Crosstalk
Получение коротких терагерцовых
импульсов
Результаты измерений
Folie 25
Problems
Radiation pulses in the range 0.1 – 1 THz
Pulse duration 10 – 20 ps
Available detectors
Slow – semiconductor bolometers (linear)
Fast – superconducting electron bolometers (linear)
Fast – superlattice detector (non-linear)
Beam size a few millimeters & detector size a few
micrometers
Antennensimulation
Au-Antenne (100nm) auf Saphir
S11=-18 dB bei f = 0,95 THz
Antennen + Filter Layout
Gesamtstruktur
Antennen + Filter S-Parameter im THz-Bereich
• S11 = S22 = -43 dB bei 0,95 THz• S21 = S12 = -32 dB sowie S31 = S32 = -24 dB bei 0,95 THz
Signal wird gut inAntenne eingekoppeltund nur wenig reflektiert
Folie 30
Martin-Puplett Interferometer
Output
Input 1
Input 2
Typical autocorrelation signal
Detector signals seem to overlap over the whole scan lengthNegative autocorrelation signalNeither the peak at 0 nor the whole response corresponds with the
streak camera measurementsPeriod of about 20 psPeak at zero shorter than the other peaks
-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60
0.0
0.5
1.0
Normalize to [0, 1] of B GaussAmpFit von C
Nor
mal
ized
Aut
ocor
rela
tion
sign
al
Time (ps)
Beam parameter: 629 MeV, 480 kV, 7.05 kHz, 100mA beam current
Streak camera: FWHM) = 26ps
Combination from crosstalk correlationand field correlation
Folie 32
Field detector
0.0 0.2 0.4 0.6 0.8 1.0-5
0
5
10
TH
z re
spo
nse
(m
V)
Time (ns)
Dielectric mirror Metallic mirror
I = const0
I1
R1
I2
R2
(t) (t+ )
Folie 33
Field autocorrelation
Two ultra-short pulses (a) and (b) with their respective field autocorrelation (c) and (d). Note that the autocorrelations are symmetric and peak at zero delay. Note also that unlike pulse (a), pulse (b) exhibits an instantaneous frequency sweep, called chirp, and therefore contains more bandwidth than pulse (a). Therefore, the field autocorrelation (d) is shorter than (c), because the spectrum is the Fourier transform of the field autocorrelation (Wiener-Khinchin theorem).
Folie 34
Autocorrelation with superlattice detector
S. Winnerl et al., APL 1998
Combination from field and intensity correlation
Folie 35
Thank you