thz generation and transport
Post on 10-Jan-2016
38 Views
Preview:
DESCRIPTION
TRANSCRIPT
THz generation and transport
Sara CasalbuoniDESY Hamburg
S. Casalbuoni, DESY
Overview
• Motivation • Design goals • Simulation tools - POP ZEMAX
- Mathematica code (B. Schmidt, DESY)
• THz beam extraction• Optical design• Simulation of the THz radiation transfer line• Summary and outlook
S. Casalbuoni, DESY
Motivation
CDR/CTR
140 m, = 1000, Eel = 500 MeV
Bunch length measurements with interferometer
S. Casalbuoni, DESY
Design goals
• Flat frequency response
• Low frequency response limit as low as possible BUT– Finite dimensions of transfer line tube and mirrors (ɸ ≈ 200mm)– Long transfer line ~20m
• High frequency structures expected from μbunching up to 30THz(10μm)
S. Casalbuoni, DESY
30THz
Diamond window
S. Casalbuoni, DESY
Vacuum needed
0 200 400 600 800 10000.0
0.2
0.4
0.6
0.8
1.0
Transmission through 20m of Humid Air (50% RH)
Tra
smis
sio
n
(m)
vacuum pressure(mbar) 1000 100 10 1 0.1 0.01
from B. Schmidt
S. Casalbuoni, DESY
LL
yx
L
yxLd
Lyx
L
y
L
xLdyxLd
dddi
eELyxE
ikd
Surf
22
|||,|
1;)()(
),0,,(~
),,,(~
2222
222222
),(
Simulation ToolsZEMAXCommercially availablePOP (Physical Optic Propagation)
B. Schmidt (DESY)Mathematica
2 CODES
Huygens-Fresnel principle:Every point of a wave front may be considered as a centre of a secondary disturbance which gives rise to spherical wavelets, and the wave-front at any later instant may be regarded as the envelope of these wavelets. The secondary wavelets mutually interfere.
ƞ
ξy
x
L
d
first order second orderFraunhofer near field, Fresnel
≃Lfinite size screen
Kirchhoff integral
S. Casalbuoni, DESY
Input for CTR
rII
rII
ck
;)(kb/I
)(kb/K )/(k)(kr/)(kr/K )/(kIr)(k,E
~
;)(kb/I
)(kb/K )/(k)(kr/)/(kK )(kr/Ir r)(k,E
~
//2radius pipebradius beamcoordinate radialr
0
01111r
0
01111r
Fourier Transform with respect to the longitudinal coordinate ζ=z-vt of the radial electric field Er of a uniform bunch charge distribution of radius ρ moving with velocity v in straight line uniform motion (M. Geitz, PhD Thesis).
sinE~ E
~cosE
~ E
~atan(y/x)
ryrx
S. Casalbuoni, DESY
Ginzburg-Frank
L
x
Lx
LxLxI
))/(sin1(
)/(sin)/(
22
22
Valid: - if CTR screen radius ≳ effective CTR radius a ≳ λ -if L ≫ λ 2 ⇒ far field (Castellano & Verzilov, Phy.Rev.ST-Accel. Beams ,1998)
⇒ frequency independent
-8 -6 -4 -2 0 2 4 6 80.0
0.2
0.4
0.6
0.8
1.0
Inte
nsi
ty
(a.u
.)
S. Casalbuoni, DESY
from P. Schmüser
Both conditions satisfied
=300μmL=10m
a=30mm
S. Casalbuoni, DESY
from P. Schmüser
Finite size CTR screen
=1.5mmL=20m
a=30mm
S. Casalbuoni, DESY
from P. Schmüser
Near field
=300μm
L=0.5m
a=30mm
S. Casalbuoni, DESY
L=0.5m a=30mm
from P. Schmüser
Both conditions violated
=1.5mm
and exact SQRT
S. Casalbuoni, DESY
ZEMAXCommercially availablePOP (Physical Optic
Propagation)
B. Schmidt (DESY)Mathematica
Both make use of scalar Fresnel diffraction theory
2 CODES
Valid if objects and apertures >> λ|x-ξ|,|y-η|<<L
ξ
ƞ
x
y
L
Fourier transform of
ck
ddeeEeLi
LyxE LyxikLik
Surf
Lyxik
2;
2
2/)(2/)(
),(
2/)( 2222
),0,,(~1
),,,(~
ddeEdi
LyxE ikd
Surf
),(
),0,,(~1
),,,(~
Simulation Tools
S. Casalbuoni, DESY
Free propagation
0 20 40 60 80 1000.0
0.2
0.4
0.6
0.8
1.0 (mm) f(THz) 1 0.3 0.1 3 0.01 30 0.001 300
Inte
nsity
(a.
u.)
X (mm)
if a ≲ λ and/or L ≲ λ 2 ⇒ I (x, L,ω) frequency dependent
L=1 m; a=10 mm; =1000
S. Casalbuoni, DESY
Dimensions of the CTR screen
-10 -5 0 5 100
1
2
3
ZEMAX Mathematica
screen intensity @window/@screen (mm)
10 0.74 20 0.84 25 0.83 30 0.79 40 0.70
Inte
nsity
(a.
u.)
X (mm)
window =20mm
L=40mm; =1000λ=1.5mm ⇒ f=200GHz
S. Casalbuoni, DESY
CDR screen
intensity @window/@screen 0.75 0.55 0.78
20 mm
ɸ=20 mm, slit=1mm
ʘ ʘʘ
window =20mmL=40mm; =1000λ=1.5mm ⇒ f=200GHz
ɸ=20 mm
S. Casalbuoni, DESY
Optical design: technical drawing
from O. Peters
S. Casalbuoni, DESY
Optical design
CTR screen ɸ=25mm
diamond window ɸ=20mm
M1 f=630mm ɸ=188mm
M2 f=4500mm ɸ=188mm
M3 f=3500mm ɸ=188mm
M4 f=3000mm ɸ=188mm M5 f=100mm
ɸ=100mmfinal screen
40mm 560mm 3410mm 8990mm 3100mm 2400mm 100mm
M1600mm
M2 M3
M4M5
8990mm
2400mm100mm
3100mm
3410mm
S. Casalbuoni, DESY
Simulation of the THz radiation transfer line with ideal thin lenses
λ=1.5mm ⇒ f=200GHz; =1000
Intensity @final screen/@window=0.49
CTR screen ɸ=25mm Diamond window ɸ=20mm M1 M2
M3 M4 M5 final screen ɸ=8mm
S. Casalbuoni, DESY
-10 0 100.000
0.001
0.002
0.003
-60 0 600.00000
0.00002
-100 -50 0 50 1000.00000
0.00001
0.00002
-100 -50 0 50 1000.000000
0.000005
0.000010
-100 -50 0 50 1000.00000
0.00002
0.00004
0.00006
-50 0 500.00000
0.00005
-10 -5 0 5 100.000
0.005
0.010
M5M4M3
M2
Inte
nsity
(a.
u.)
Mathematica ZEMAX
M1
final screen
Inte
nsity
(a.
u.)
X (mm)
X (mm)
Inte
nsity
(a.
u.)
X (mm)
diamond window
Simulation of the THz radiation transfer line with ideal thin lenses
λ=1.5mm ⇒ f=200GHz =1000CTRscreenɸ=25mmDiamond windowɸ=20mm
Intensity @final screen/@window=0.49
S. Casalbuoni, DESY
-10 0 100.000
0.001
0.002
0.003
-60 0 600.00000
0.00002
-100 -50 0 50 1000.00000
0.00001
0.00002
-100 -50 0 50 1000.000000
0.000005
0.000010
-100 -50 0 50 1000.00000
0.00002
0.00004
0.00006
-50 0 500.00000
0.00005
-10 -5 0 5 100.000
0.005
0.010
M5M4M3
M2
Inte
nsity
(a.
u.)
intensity @final screen/@CTR screen
CTR 0.49 Gauss beam 0.85
w0=9mm
M1
final screen
Inte
nsity
(a.
u.)
X (mm)
X (mm)
Inte
nsity
(a.
u.)
X (mm)
diamond window
Good also for a Gaussian beam
λ=1.5mm ⇒ f=200GHz =1000CTRscreenɸ=25mmDiamond windowɸ=20mm
S. Casalbuoni, DESY
Simulation of the THz radiation transfer line at different frequencies
-4 -2 0 2 40.000
0.005
0.010
(mm) f(THz) 1.5 0.2 0.3 1 0.01 30
= 1000 CTR screen = 25mmdiamond window = 20mm
final screen =8mm
Inte
nsity
(a.
u.)
X (mm)
Intensity @final screen/@window
0.490.900.99
S. Casalbuoni, DESY
Transfer function
0.1 1 10
1E-5
1E-4
1E-3
0.01
0.1
1
Inte
nsi
ty @
fina
l scr
ee
n/@
win
do
w
f(THz)
λ(mm) 3 0.3 0.03
S. Casalbuoni, DESY
Half screen and horizontal polarization: frequency response
-4 -2 0 2 40.00
0.01
0.02
(mm) f(THz) 1.5 0.2 0.3 1 0.01 30
= 1000 CTR screen = 25mmdiamond window = 20mm
final screen =6mm
Inte
nsity
(a.u
.)
X (mm)
Intensity @final screen/@window
0.520.91 0.99
ʘ
S. Casalbuoni, DESY
Gaussian beam λ=500nm
M3 M4 M5 final screen
w0=1mm Diamond window ɸ=20mm M1 M2
S. Casalbuoni, DESY
Summary and outlook
• 2 simulation tools: very good agreement
• Optical design for the THz beam line transfer @140m in TTF2: tested for CTR, CDR and Gaussian beam
• Outlook
-”ideal” mirror surface
-tests for stability against beam displacement and mirrors misalignment
-effect of tilting CTR screen
S. Casalbuoni, DESY
Electric field of a charge in the laboratory system
krK
kqrkE
derkErkE
ctzvtz
rvtz
rqEE
r
rqrE
r
ikrr
rz
10
2/32220
32/322
2
0
4),(
~
),(),(~
)(4;0
sin1
)1(
4)(
q
)(rE
observation point
r
vθ
S. Casalbuoni, DESY
L ≫ λ 2 far field⇒
22
22222
1)(
)(12
)(
LL
L
k
characteristic size of theCTR screen
S. Casalbuoni, DESY
Paraboloid mirrorsCTR screen ɸ=25mm Diamond window ɸ=20mm M1 M2
M3 M4 M5 final screen
S. Casalbuoni, DESY
Paraboloid mirrors
-10 0 100.000
0.001
0.002
0.003
-60 0 600.00000
0.00002
-100 -50 0 50 1000.00000
0.00001
0.00002
-100 -50 0 50 1000.000000
0.000005
0.000010
-100 -50 0 50 1000.00000
0.00002
0.00004
0.00006
-50 0 500.00000
0.00005
-10 -5 0 5 100.000
0.005
0.010
m4m3
m2
Inte
nsity
(a.
u.)
m1
m5
final screen
paraxial lenses paraboloids
Inte
nsity
(a.
u.)
X (mm)
X (mm)
Inte
nsity
(a.
u.)
X (mm)
window
S. Casalbuoni, DESY
Transfer function
0.1 1 10
1E-5
1E-4
1E-3
0.01
0.1
1
lenses paraboloids
Inte
nsi
ty @
fina
l scr
ee
n/@
win
do
w
f(THz)
S. Casalbuoni, DESY
Paraboloid mirrors: half screen and horizontal polarization
Half CTR screen ɸ=25mm Diamond window ɸ=20mm M1 M2
M3 M4 M5 final screen
Intensity @final screen/@window 0.64
top related