ep-dt thin film and glass service (tfg) · ep-dt-tfg anti reflective coating dt training seminar t....

•Thin film coating

•Glass & ceramic machining

•Optics Quality Control lab

•Apprentices training (~3*3months)

•General support to DT detector projectsSee link=> https://ep-dep-dt.web.cern.ch/thin-film-glass-service

EP-DT Thin Film and Glass Service (TFG)

Jerome NoelThomas SchneiderMiranda van Stenis Laura Funder (technical student)

More than 50 years growing experience

1DT training seminar T. Schneider 8/4/2020

Florian Jenny(apprentice)

ProductionStandard service

R&D

EP-DT-TFG Anti Reflective coating


Improve Transmission of LHCb RICH1 quartz

exit window

A thin transparent layer of MgF2 (n2 different to n1

substrate) is applied via thin film coating to reduce

Fresnel reflection . By setting the thickness of the

coating to a quarter wavelength, the second

reflection R2is delayed by λ

2. This opposite light

wave reduces (cancelation) the initial reflection.

Refractive index n2

Refractive index n1

i r

r’

FRESNELReflection(R)

Refraction

I0

2

12

12

nn

nnR

λ/2

EP-DT-TFG Enhanced reflective coating


λ delay

Enhanced reflective coating

Aluminum as very uniform metallic

reflector is deposited on a polished

substrate. On top a dielectric

transparent layer is applied to enhance

the reflectance of the Aluminum layer.

In this case the layer thickness (~ λ/2)

is adjusted such that the 2nd reflection

is delayed by λ. That way the 2

waveforms overlap and add up.

In addition this dielectric layer act as

protection layer for the Aluminum.

(oxidation and mechanical handling)

EP-DT-TFG LHCb RICH1 upgrade


R&D for LHCb RICH1 optics system (status mid 2019)

• Defined recipe for enhanced protected coating according to given requirements (sensitivity of photo detector 250-500nm)

• Test coating on real size flat mirror (Cr, Al, SiO2, HfO2)

• Overcome intrinsic problem of big spherical mirrors (thinner layers @ borders)

• Test coatings on composite samples

16 flat glass mirrors(370mm*440mm) 4 spherical composite mirrors, (740mm*650mm)

Quartz window QC


The dimensions of the spherical composite substrates have been adapted to the geometrical limits of the coater.These will be the largest mirror substrates ever treated in the TFG lab.

4 spherical composite mirrors, Diagonal 965mm

5DT training seminar J. Nôel 8/4/2020


Big Coater “clean” room B108

Vacuum Tankinner space Ø970 mm

6

E beamPower rack

Process protocolLab view softwareData Acquisition

Cryo pump :Vacuum : 10E-8 mbar

Inficon module :Thickness measurementThermal source processingRotation 60 rpm

DT training seminar J. Nôel 8/4/2020


Rotating substrate holder

X-talThicknessmeasurement

T° sensors

7

Electron Beam source4 crucibles

Thermal sources2 slots :

spring or crucible

Big Coater “clean” room B108


8


LHCB spherical composite mirrors thin film recipe

Adherence layerCr

1st

Metallic reflexionAl

2ndSiO2

3rd

HfO2

4th

Ther

mal

Ther

mal

E B

eam

E B

eam

Enhancement of the reflectivity+ protecting the Al


Dielectric layers with ~30% of thickness variationAt the corners of the big spherical composite mirrors.

Big Coater 108 E beam : relative thickness distribution on a turning substrate

Dielectric layers with 10% of thickness variationAt the corners of the small rich mirror



Big Coater E beam : Thickness variation = reflective variation

Working range of the optical chain is within a wavelength of 275nm - 390nm


10

Small mirrors

Big mirrors

Agreed requirements for Work Package TFG -LHCb RICH1 (EDMS 2060758) 2017Big spherical mirrors:Reflectivity >90% in the range 280nm-380nmSmall flat mirrors: Reflectivity >90% in the range 280nm-500nm


Simulation of the thickness variation on the 4 RICH spherical composite mirrors

10% < Thickness variation < 30%

LHCB Beam pipe center


11

Coater center

Thickness variation < 10%


1- Mask the over exposed areas :Adding a mask in between the E beam and the substrate

Big coater upgrade to make dielectric layers uniform with the E beam on the big substrate


Shaping and sizing the mask.


Precise positioning of the shadow mask for the reproducibility

LED projector Mask Shadow of the Mask


Substrate target

Chrome evaporation's mapping with a fix substrate


2- Electron Beam upgrade for big substrate :


14

Our standard :Small spot

Reducing the border effect and stabilize the beam rate deposition :- Software improvement to position the beam spot with higher accuracy.- Beam spot size optimisation to keep angle distribution most constant during the process.

The walls of the deep groove acts as a mask

To achieve the thickness with the mask we need to do two deep grooves.

Two stepsSpot beam

One stepNEW square beam

Two stepsSpot beam

One stepNEW square beam



Reflectivity measured on samples with all the upgrades

15

Working range of the optical chain is nowwithin a wavelength of 260nm - 500nm

Small mirrors

Big mirrors


Reflectivity > 90% in the range of 270nm to 500nmup to Ø965mm substrate.


As good uniformity results on big spherical as on small flat mirrors!!!

16

Thickness variation < 10%

Achievements of 2019 upgrade with mask and E-beam optimisation:

Small mirrors are ongoing 4 out of 22 are done.We are ready to do the 4 big mirrors


EP-DT-TFG Questions

17DT training seminar L. Funder 8/4/2020

Questions?

ep-dt thin film and glass service (tfg) · ep-dt-tfg anti reflective coating dt training seminar t....

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