Download Quality control facilities for large optical reflectors at ENEA

Quality control facilities for large
optical reflectors at ENEACasaccia for physics application
Stefania Baccaro a,d, Carlo Bosio b,d, Augusto Maccari c,
Marco Montecchi a,d
a) ENEA FIS-ION, Casaccia, Roma, Italy
b) Dipartimento di Fisica Università La Sapienza, Roma, Italy
c) ENEA SOLTERM, Casaccia, Roma, Italy
d ) INFN – Sezione di Roma1, Roma, Italy
Large optical reflectors are used in…
• Astronomy: in telescope (imaging)
• High Energy Physics: in RICH, to
focus Cherenkov radiations on
optical sensor (quasi-imaging)
• ……
• Solar Energy: as sun-power
collectors (collecting)
… for information completeness
• How large? Single panel, up to some
meters
• Imaging use is much more demanding
than collecting one
• Composition and shape are designed for
the specific application and .....
... HAVE TO BE TESTED !!!
Irradiation plants at
ENEA – Casaccia
• TAPIRO: fast neutrons
• TRIGA: thermal neutrons
• CALLIOPE: 1.17 and 1.33 MeV 
Optical laboratory tender to Calliope:
 spectrophotometers and spectrometer
 Light-Yield
 damped optical top with light sources, lenses,
mirrors, detectors, etc..
 custom set-up
Optical tests at ENEA-Casaccia
Reflectance:
 spectrophotometer – specular and diffused (small flat sample)
 spectrometer – specular (full scale reflector)
Shape performances:
 2f optical test
 pin-hole optical test
 profilometer
focal length and image spot dimension
visual inspection of the curvature
accurate measurement of the curvature
2f optical test:
focal length and image-spot dimension
LED ( = 5 mm)
image
screen
2f
in the ideal case, image and source have the same dimension
Pin-hole optical test:
a visual inspection of the curvature
LED
surface
image
pin-hole f1
2f
p
q
where the surface image is dark, the curvature is wrong
LHCb RICH mock-up: carbon fiber
+ honeycomb
 ~ 600 mm 2f = 1700  20 mm
 image spot ~ 15 mm
LHCb mock-up : polymethylmethacrylate
(PMMA) hot bended and honeycomb
 ~ 400 mm 2f = 2370  20 mm
image spot ~ 25 mm
LHCb RICH mock-up:
PMMA poured liquid on master
 ~ 350 mm 2f = 2330  20 mm
LHCb mock-up: electrodeposited Ni
 = 200 mm 2f = 315  5 mm
Accurate test of the reflector
curvature: profilometer
 In the framework of the Concentrating Solar
Power Project, ENEA is providing with an optical
profilometer to test large linear parabolic reflectors
 the measurement is automatic - PC controlled
 the profilometer can be used also for reflectors
differently shaped (e.g. spherical reflector)
 actually the instrument performs 1D scanning
 2D upgrade is imminent
ENEA optical profilometer (1D)
rotation axis
x
screen

xS
(xC,yC)
x0
HeNe
Nikon D1X,
4.024 x 1.324 px
y
yS
• the
surface is scanned by tilting the incident beam () with a
high precision rotation stage (20 rad repeatability)
• the intersection of the reflected beam with the screen (XS) is
deduced by processing the digital image
Data processing – 1th method: fit
y = f (x,p1,..,pM)
x

x0
xS simulated
xS experimental
y
yS
best fit by minimising

 xS  xS
MF  p1 ,.., pM    
 Err  xS 
j 1

N
sim
exp
 
j


2
Data processing - 2nd method:
iterative extrapolation (I.E.)
A P
2
central point ( = 90°):
x
B
C
set dy/dx = 0 by tilting
x0
P1
the next point P2 is:
 along the incident beam, by definition
 in AB, if  1;  P1C, P2C  P1P2
 univocally determined by assuming:
P2
P1
C
y
P2
y = x2
circular:
P1C =CP2


(xc,yc) directly measured
P1
x1 xC x2
yS
parabolic:
xC = (x1+x2)/2
Example: reduced scale linear
parabolic reflector (aperture 0.6 m)

P4 2
  (1  P4 ) 2 f 

4f
rotational measurement
52
50
XS (cm)

best fit parameters:
2 = 1.23 (32/49 data)
P4 = 0.32  0.04
= 11.3  0.8 deg
f = 185.5  0.5 mm
experimental
best fit of 32/49 data
48
46
44
42
2 f 2   2 
40
38
36
34
32
30
28
26
24
22
high precision
60
70
80
90
 (deg)
100
110
120
comparison of the two methods
profile
slope
1
40
0
30
-1
20
atan(dY/dx) (deg)
-2
-3
Y (cm)
best fit
extrapolation
-4
-5
-6
-7
best fit
extrapolation
-8
10
0
-10
-20
-30
-9
-40
-20
-10
0
10
20
-20
X (cm)
-10
0
10
X (cm)
 I.E. method gives a realistic profile of the reflector
 I.E. method allows to evaluate the locale deviations from the project
specifications of both profile and slope
20
validation of the iterative
extrapolation method
profile deviation from circle r = 376mm
3.5
3.0
comparator
iterative extrapolation
2.5
radial deviations (mm)
direct measurement
comparator
2.0
1.5
harm
1.0
rotation stage
0.5
0.0
-0.5
reflector
-1.0
-20
-10
0
X (cm)
10
20
Conclusions
The ENEA-Casaccia facilities allow to
measure the most important features of
large optical reflectors:
 specular and hemispherical reflectance
 focal length
 surface profile
2D upgrade of the profilometer is imminent