Quality control facilities for large optical reflectors at ENEA-

Casaccia for physics application

Stefania Baccaro a,d, Carlo Bosio b,d, Augusto Maccari c, Marco Montecchi a,d

a) ENEA FIS-ION, Casaccia, Roma, Italyb) Dipartimento di Fisica Università La Sapienza, Roma, Italy

c) ENEA SOLTERM, Casaccia, Roma, Italyd ) 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

spectrophotometer – specular and diffused (small flat sample)

spectrometer – specular (full scale reflector)

2f optical test focal length and image spot dimension

pin-hole optical test visual inspection of the curvature

profilometer accurate measurement of the curvature

Shape performances:

Reflectance:

2f optical test:focal length and image-spot dimension

2 f

screen

image

LED ( = 5 mm)

in the ideal case, image and source have the same dimension

Pin-hole optical test:a visual inspection of the curvature

where the surface image is dark, the curvature is wrong

surfaceimage

2 f

LED

pin-hole f1

p q

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)

x

HeNe

screen

y

x0xS(xC,yC)

yS

Nikon D1X, 4.024 x 1.324 px

rotation axis

• 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

N

j S

jSS

M xErr

xxppMF

1

2expsim

1,..,

x

y

x0xS simulated

xS experimental

yS

y = f (x,p1,..,pM)

y = tg() (x - x0)

best fit by minimising

Data processing - 2nd method:iterative extrapolation (I.E.)

the next point P2 is: along the incident beam, by definition in AB, if 1; P1C, P2C P1P2

univocally determined by assuming:

yS

central point ( = 90°):

(xc,yc) directly measured

set dy/dx = 0 by tilting

x

y

x0

AB

P1

P2

C

P1

P2

C

circular:P1C =CP2

P1

P2

x1 x2xC

y = x2 parabolic:

xC = (x1+x2)/2

Example: reduced scale linear parabolic reflector (aperture 0.6 m)

60 70 80 90 100 110 12022

24

26

28

30

32

34

36

38

40

42

44

46

48

50

52

rotational measurement

XS (

cm)

(deg)

experimental best fit of 32/49 data

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

22

424 22)1(

4 ffP

f

P

high precision

comparison of the two methods

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 -10 0 10 20

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1profile

Y (

cm)

X (cm)

best fit extrapolation

-20 -10 0 10 20-40

-30

-20

-10

0

10

20

30

40slope

atan

(dY

/dx)

(de

g)X (cm)

best fit extrapolation

validation of the iterative extrapolation method

direct measurement

-20 -10 0 10 20-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

profile deviation from circle r = 376mm

rad

ial d

evi

atio

ns

(mm

)

X (cm)

comparator iterative extrapolation

comparator

rotation stage

harm

reflector

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