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					                      Advanced Virgo construction outline form

                                    Subsystem INJ
                                           Eric Genin
                                        January 2009 v3
0. Documents

Authors     Date      Title                                   Link
The         10/2007   Advanced Virgo Conceptual design        https://pub3.ego-
collabora                                                     php?doc=1900&calledFile=VIR-
tion                                                          042A-07.pdf
The         10/2008   Advanced Virgo Preliminary Design       https://pub3.ego-
collabora                                                     php?doc=2110&calledFile=VIR-
tion                                                          089A-08.pdf
LIGO        08/2007   Input Optics Subsystem                  LIGO G-07011700-00-R
Science               Preliminary Design Document
Marque,     12/2008   Advanced Virgo: INJ subsystem Design
Genin,                study.

1. Description
The INJ subsystem of Advanced Virgo takes care of the optics downstream of the high power
laser, and of the interface of these optics and the laser itself. The whole system must deliver a
beam with the required power, geometrical shape, frequency and angular stability. Given the
180-200 W power delivered by the High Power Advanced Virgo laser all the components will
have to be compliant with this high power.
An EOM system will provide the needed RF modulations (for control and sensing purposes).
A power adjustment system will be used in order to tune ITF input power (important for ITF
lock acquisition).
A matching and steering system in air will be used to couple the beam into an in-vacuum
suspended input mode cleaner (IMC) cavity.
The IMC will geometrically clean the beam and reduce its amplitude and lateral fluctuation.
The resonant IMC of which the length is locked on the reference cavity (RFC) will also serve
as a first stage of frequency pre-stabilization. After the IMC an intensity stabilization section
will provide the signal for stabilizing the laser RIN and reach the requirements (this should be
provided by PSL subsystem). An in-vacuum Faraday isolator will prevent interaction of the
ITF (interferometer) rejected light with the IMC and laser system. Finally, an ITF mode
matching telescope will give to the beam the correct dimension for matching with the
A block diagram of INJ subsystem is given in figure 1.

                                                                                          IMC Reflection

                            Figure 1 : INJ subsystem block diagram.

2. Project issues

                                        Project table
No. Task                Phase         Duration       Predecessor      Cost            Manpower
1                       Constr        6 months       Possible start   40 kE           Depends on
    Electro-optical                                  Mid 2010         (with a         the solution
    modulation                                                        spare)          chosen (see
    system                                                                            INJ Design
2                      Constr         1 month        Possible start   11 kE           0.25 opt. P or
     Input Power                                     End 2010         (with a         E
     Control                                                          spare)
3    Beam Pointing     Constr         3 months       Possible start   20 kE
     Control                                         End 2010
4    Input Beam Jitter Constr         2 months       Possible start   5 kE
     Monitoring                                      End 2010
5                      Constr         6 months       Possible start
     Input beam                                      Mid 2010

6                       Constr        7 months       Possible start   Depends on
     Input mode-                                     Jan 2010         the chosen
     cleaner (mirrors                                                 configuration
     polishing and

6                        Constr       4 months       Possible start   Depends on
     Input mode-                                     Mid 2010         the chosen
     cleaner (mirrors                                                 configuration
6    Input Mode          Inst         2 months       Possible start                   Depends on
     Cleaner                                         Jan 2012                         the solution
                                                                                      chosen (see
                                                                                      INJ Design
7    UHV Faraday         Constr       6 months       Mid 2010         80kE (with      External
     isolator                                                         one spare)      production
7    UHV Faraday         Inst         0.5 month      New SIB                          2 optical P or
     Isolator                                        ready for                        E
     installation                                    assembling
8    Other Faraday       Constr       3 months       Possible start   40 kE
     Isolators                                       End 2010
8    Other Faraday       Inst         0.25           FI compliant                     2 opt. P or E
     Isolators                        month          with high                        1 electr. E
     installation                                    power
                                                     ordering and
9    RFC vacuum          Constr       2 months       Possible start   20 kE
     pieces                                          Jan 2011
9    Reference           Inst         1.5 month      Vacuum                           Depends on
     Cavity                                          pieces                           the solution
     installation                                    purchased                        chosen (see
                                                     and ready to                     INJ Design
                                                     be installed                     finalization
10   IMC Mode            Inst         0.5 month      AdV Laser        20 kE           2 opt. P or E
     Matching                                        beam
     Telescope                                       available and
                                                     IMC cavity
11   ITF Mode            Inst         0.5 month      New SIB          5 kE            2 opt. P or E
     Matching                                        ready for
     Telescope                                       assembling
12   Assembling of      Optical      6 months        Design           245 kE          2 opt. P or E
     the various        and                          choice made
     subsystems         mechanical
     together           Design +
Legend: P=physicist, E=engineer, T=technician, ...

It is not possible for the moment to give an accurate estimation of time and cost required for
each tasks since there are a lot of open points where an answer should come the design study
that should be completed not before May 2009.

A. Deliverables
EOM: We should provide and EOM system able to modulate the laser beam as required by
ISC subsystem (for ITF and IMC control and locking purpose). The modulation electronics
will have to be properly designed and characterized to be compliant with AdV requirements.

Input Power Control (IPC): With this system we should be able to remotely tune the laser
power from low (a few watts) up to full power. This system will be based on Virgo+ IPC
system. The laser power should be adjusted in two points of INJ subsystem. Before the IMC
cavity and on the suspended injection bench after optical elements that are sensitive to laser
beam heating in order to adjust the laser power at the interferometer input port.

Beam Pointing Control: The aim of this control loop is to reduce angular beam jitter and shifts
of the beam at low frequency before entering vacuum vessels. Dedicated sensors will have be
developed starting from Virgo experience in this field.

Input Beam Jitter Monitoring: We should provide a system that monitors beam shifts and tilts
on the whole sensitivity curve bandwidth. The main concern is about the sensor choice and
the proper design of the dedicated electronics to detect very low jitter noise on the 10 kHz

Input Beam Spatial and Spectral Characterization system: It should provide some useful tools
to characterize ITF input beam properties. This characterization should be done by different
    - Beam imaging in order to extract geometrical properties of the beam
    - Beam quality (higher order modes content beam spectral characterization ).
    - Sidebands characterization before entering the ITF.

Input Mode Cleaner cavity: The input mode cleaner should provide active frequency
stabilization through feedback to the Laser, passive frequency noise suppression above its
cavity pole frequency, and passive spatial stabilization at all frequencies. The input mode
cleaner should also reduce higher order modal content of the laser beam entering the vacuum
vessels. A locking electronics will have to be provided as well as an automatic aligment
system (opto-electronic control loops will have to be designed and carried out).

Faraday Isolators:
High power compatible in-vacuum faraday isolator compensated in term of thermal lensing
and depolarization. A remote adjustment of the isolation should also be provided.

Reference cavity: A cavity used a reference to control and the IMC cavity length and lower
the laser frequency noise in order to lock the Fabry-Perot cavities should be provided.
According to preliminary calculations Virgo reference cavity should fulfil AdV requirements.

IMC Mode Matching Telescope:
A telescope to match the laser beam and maximize the coupling into the IMC cavity should be
designed and carried out. It could be interesting to have this device remotely adjustable.

ITF Mode Matching Telescope:
The same kind of telescope has to be built to match the IMC output beam onto the
interferometer (ITF). This telescope has to be vacuum compatible and should be remotely
adjustable. Choosing a non-degenerate power recycling cavity will relax a lot the work on this

Assembling of the various subsystems together:
All the various subsystems of INJ have to be assembled. A general layout of in-air and in-
vacuum benches has to be given. From the layout, optics, electronics and mechanics parts will
be designed, selected and purchased (optics mounts, optical benches, actuators, sensors,…).
These parts will have to fulfil AdV requirements. In particular, low scattering optics and
mechanical mounts specially designed to avoid low frequency resonances should be used in
order to reduce environmental noise coupling.

B. Time planning

This time planning will be given later on.

C. Subsystem interdependencies
External predecessors
For all the different parts of INJ system, we will need:
    - Infrastructures ready (Air conditioning, room)
    - INJ and MC tower super attenuators upgraded as required for AdV.

  - Modulation frequencies and modulation depth are need from ISC.
  - Prototype from HPIO R&D (crystal selection, modulation electronics).
  - Information on laser output beam size is required from LAS.

Input Power Control (IPC):
   - AdV laser should be installed.

Beam Pointing Control:
   - Requirements on beam jitter should be given before designing the system (sensors and
      actuators selection and optical design).

Input Beam Jitter Monitoring:
   - Requirements on beam jitter monitoring should be given before designing the system
       (sensors selection and electronics realization).

Input Beam Spatial Characterization system:
   - Characterization means have to be defined (scanning cavity, beam imaging and beam
       size measurement systems,…).

Input Mode Cleaner cavity:
   - Requirements on laser frequency prestabilization, Intensity noise filtering and passive
       beam jitter filtering should be given to freeze IMC cavity parameters (Finesse, mirrors
       reflectivity,…). These requirements should be given by OSD and ISC subsystems.

Faraday Isolators:
   - Requirements on Faraday isolator isolation should come from IMC cavity design
   - UHV compatible faraday isolator that is compensated for depolarization, thermal
       lensing and where the isolation is remotely tuneable (as done in Virgo+) should be
       studied by IAP group (Novgorod, Russia).
   - From the design study, a prototype should be built.
   - SIB optical design (faraday integration).

Reference cavity:
   - Simulation (RFC FEM simulation).
   - Evaluation of EIB-SIB differential motion.
   - EIB optical design.
   - SIB optical design.
   - Requirement for locking (locking strategy) given by ISC subsystem.

IMC Mode Matching Telescope:
  - IMC cavity parameters (waist size, waist location).
  - Optical simulations using an optical simulation software (Zemax, Code V,…).

ITF Mode Matching Telescope:
   - ITF parameters (waist size, waist location).
   - Optical simulations using an optical simulation software (Zemax, Code V,…).

Assembling of the various subsystems together:
   - Laser output beam and ITF input beam characteristics (waist size, waist location) are
      required from LAS and OSD.
   - Optical simulations using an optical simulation software (Zemax, Code V,…).

External successors

  - IMC cavity and Interferometer locking and alignment activities will require the
     installation of the EOM system.

Input Power Control (IPC):
   - IMC and ITF locking strategy at different laser power levels.

Beam Pointing Control:
   - Required to commission the ITF and reach high sensitivity at low frequency.

Input Mode Cleaner cavity:
   - Power stabilization and Laser frequency pre stabilization loops commissioning.
   - Interferometer installation (core optics installation and alignment) and commissioning.

Faraday Isolators:
   - Required to lock the interferometer to avoid sending back the ITF reflection in the
       IMC cavity (can be uncontrollable) and in the laser (can be damaged).

Reference cavity:
   - Laser frequency stabilization loop commissioning.
   - AdV Interferometer locking activities.

IMC Mode Matching Telescope:
  - IMC cavity commissioning (locking and alignment system).

ITF Mode Matching Telescope:
   - Interferometer commissioning (locking and alignment system).

Assembling of the various subsystems together:
   - INJ subsystem installation and commissioning.
   - Interferometer alignment and commissioning.

D. Cost
A rough estimation of INJ subsystem cost is given in Table 1.

Item                                                                    Price (kE)
Ultra high vacuum Faraday isolator                                                                             80
EOM system                                                                                                     40
Input power control                                                                                            11
Beam pointing control                                                                                          20
Quadrant photodiodes                                                                                            4
Actuators                                                                                                      12
Mechanics                                                                                                       3
Input beam jitter monitoring                                                                                    5
Quadrant photodiodes                                                                                            4
Mechanics                                                                                                       1
Input beam spatial and spectral characterization system                                                        30
In-air high power compliant faraday isolators                                                                  40
RFC (vacuum pieces(pump,...))                                                                                  20
IMC mode matching telescope (optics, electronics, mechanical
mounts,...)                                                                                                    20
ITF mode matching telescope (optics, electronics, mechanical                  Depends on Recycling cavity optical
mounts,...)                                                                          configuration (5 kE if NDRC)
Assembling of the various INJ parts together                                                                  245
Polarizers                                                                                                     20
Low-scattering in-air optics                                                                                   50
In-air mechanics                                                                                               60
Suspended injection bench mechanics (excluded IMC and PR mirrors
suspensions)                                                                                                   30
Other optics (waveplates, mirrors, lenses,...)                                                                 20
Vacuum compatible electronics                                                                                  50
In-air electronics (photodiodes (single element and quadrant), locking
electronics)                                                                                                   15
New resonant Input Mode-Cleaner (mirrors, mechanics,
electronics,…)                                                                                                150
TOTAL                                                                                                         666
                      Table 1 : Rough cost estimation of INJ subsystem by construction task.

This estimation has been given without taking into account the taxes and the total cost is
about 666 kEuros with spare parts.
For the specific item of ITF mode matching telescope, a contingency of about 100 kEuros has
to be considered if it is decided not to use the Non Denegerate Recycling Cavity
configuration. In this case, the ITF mode matching telescope will have to be an off-axis
parabolic telescope of the same kind that what is currently used in Virgo. Due to cavity
geometry, the second mirror of this telescope will have to be at least 300 mm diameter to
avoid clipping losses.
A 10 % contingency for the rest should be foreseen since a lot of parts should be bought in the
USA and are obviously depending on Euro/Dollar exchange rate.

E. Manpower
The manpower given in the project table is very rough and based on past experience in Virgo.
This will be completed once we will know the technical solution chosen for each part of INJ

F. Construction/installation responsibilities

EOM: EGO lab, who has an extensive experience on this item and that is the principal
investigator of HPIO R&D program that aims to select and carry out a prototype compliant
with AdV needs, is the best institute to take care of this system.

Input Power Control (IPC): The responsibility should be assigned to EGO lab since this lab
has already carried out Virgo+ IPC system.

Beam Pointing Control & Input Beam Jitter Monitoring: Virgo Beam Monitoring System that
aims to monitor and control the beam jitter is well known by EGO. EGO optics group can be
responsible for this task.

Input Beam Spatial Characterization system:
EGO group has already installed some Beam characterization tools for Virgo

Input Mode Cleaner cavity: Concerning the IMC mirrors, LMA that is already responsible for
the selection and the purchase of ITF core optics could be responsible for AdV IMC mirrors
selection and for the coating of these objects.
IMC input mirrors assembling and IMC mirrors suspension lower part : Nikhef.
For the mirrors alignment and AdV IMC installation and commissioning, EGO is the right
group to be responsible for this activity.

Faraday Isolators:
A collaboration has started in September 2008 with the Institute of Applied Physics,
Novgorod, Russia that is the specialist of High power faraday isolators. They should provide
an UHV compliant faraday isolator under the supervision of EGO staff working on HPIO
They could provide some other smaller faraday isolator to be used on the laser and external
injection benches.

Reference cavity: No particular work to be done. The only thing is to include this object in
INJ subsystem optical layout.

IMC Mode Matching Telescope:

EGO group has an extensive experience in this kind of telescope and could be responsible for
this task.

ITF Mode Matching Telescope:
APC lab has expressed the wish to work on the ITF Mode Matching Telescopes, one of these
telescopes is on the suspended injection bench and could be of the responsibility of APC even
if EGO has the required experience to deal with this task.

Assembling of the various subsystems together:
This task should be assigned to EGO group that has a lot of experience in designing Virgo and
Virgo+ optical benches (Virgo+ Laser bench, Virgo and Virgo + EIB and SIB and Virgo+ end

3. Risk
Give a list of potential problems. List first the risks during construction/installation (delays of
external firm ...) and then eventual risks during operation (failure ...).

Problem 1 (C/O) C=Construction/installation risk, O=operation risk
Describe the potential problem. Try to assess the probability that the problem occurs.
Describe to consequences of the problem. In the following table, try to give quantitative
estimates in terms of Euros, man-days of extra workforce needed, days of delay, reduced
performance of the subsystem or part of it.
Enter text here.

Extra cost
Extra needed manpower
Performance of subsystem/AdV

Describe possible solutions.
Enter text here.

Problem 2
Copy from Problem 1...


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