Lock Acquisition with Auxiliary Lasers Main Question to be answered for the design : What is the goal of auxiliary lasers ? 1. lock independently the arms before respective switch to B7/B8 2. lock both arms before switch to SSFS and DARM control 3. maintain arms locked during lock acquisition of small degrees of freedom 4. something else ?  Impact on laser stability and so, on optical design of the end benches If answer 1 or 2 is correct, some simulations are needed to rule out (or not) a standard lock acquisition of Fabry-Perot cavity using a servo. simulation of transition to main laser in the AdV case has to be done. Transition scheme will also be tested in CALVA : offset in the control loop, frequency shift (controlled or free)

Transition from auxiliary laser to main laser Simulation performed on a single CALVA cavity using e2e : Shotnoise, laser frequency noise and radiation pressure effect included 1 FP ( F =1200) cavity illuminated by a 1 W, =1.064  m laser Auxiliary laser, P= 1 mW, l=1.6  m. Two finesses have been tested 1.6 and 4 Lock Sequence: 1.Lock auxiliary laser 2.Bring auxiliary laser to the main laser resonance using a frequency shift 3.Switch the control from auxiliary signals to main signals

Deliveries : 1.Design of optical benches a.Laser frequency stabilization b.Injection of auxiliary beams c.Detection of beams 2.Purchase of lasers 3.Purchase of optical components (modulators, Faraday isolators, rigid cavities, …) 4.Lab tests 5.Installation Planning :

Manpower and costs : Project table No.TaskPhaseDurationPredecessorCostManpower 1Design of optical benches Construction120.5 optical engineer 2Purchase of lasersConstruction optical engineer or physicist 3Purchase of optical components Construction optical engineer or physicist 4Lab testsConstruction62;30.5 optical engineer 0.5 optical technician 5Installation optical engineer 0.5 optical technician Remarks : Optical design and installation in CALVA have been performed by ESPCI group No skill at LAL for this activity.

Dependencies : MIR : Optical properties of coating at the auxiliary wavelength OSD : For the definition of optical parameters DET : Integration of the auxiliary lasers on the end benches Photodiodes for auxiliary lasers DAQ : acquisition of Pound-Drever signals generated by auxiliary lasers The most critical part is the integration on the end benches. The design has to be done with great care in order to avoid spurious beams and diffused light which can bring some noise

Conclusions Auxiliary lasers : what for ? Simulations needed to insure the need of the technique Competences to be found for bench design Validation of design and transition strategy on CALVA