MIF's Interface with IOO

Carrier

iKAGRA

Wavelength

1064nm

Comment

Power

>500mW at PRM AR

More than 1W desirable

Polarization

S

Complex beam radius at the PRM AR

9.8358048093144834+i*18.307397678406861

So called q-parameter in the unit of m. Although there is no PRM in iKAGRA, this is a beam parameter at the position where the AR surface of the PRM will be located in bKAGRA. This parameter gives the perfect mode match to the iKAGRA arm cavities. However, the MIF does not require IOO to provide 100% mode matching in iKAGRA phase. More than 60% of mode matching is the current requirement, which allows us to use the same IMMT as bKAGRA.

Frequency Noise

To be calculated from the viewpoint of lock acquisition.

Residual frequency noise after the MC.

Relative Intensity Noise

To be calculated from the viewpoint of lock acquisition.

Beam Jitter

1e-6 rad RMS

Calculated by requiring that beam spot moves less than 1mm after traveling 3km.

bKAGRA point of view

Wavelength

1064nm

Comment

Power

75W at PRM AR

Power adjustability

750mW to 75W continuous

(TODO: decide where to put variable attenuators)

Polarization

S

Complex beam radius at the PRM AR

-10.580258464886768+i*56.648923633432595

So called q-parameter in the unit of m.

Frequency Noise

BRSE, DRSE

Residual frequency noise after the MC. For more detailed discussion, see this.

Relative Intensity Noise (AF)

BRSE, DRSE

Relative Intensity Noise (RF)

< 2.7e-9 @ above f1 frequency

RF RIN at the input to the MIF (i.e. MC trans) (TODO: more detailed calculation)

RFAM amplitude

to be calculated

Static RFAM amplitude after MC.

RFAM phase jitter

to be calculated

Tolerated RFAM phase fluctuations. It should depend on the RFAM amplitude.

Beam Jitter

3e-11 rad/rtHz@10Hz, 7e-14 rad/rtHz@100Hz (Safety mergin of 20)

Detail

Modulations

iKAGRA

Name

Freqency

Type

Mod. index

Relative Amplitude to Carrier before PRM

Comment

fPMC

15MHz

PM

fIMC

51.72MHz

PM

also used for FRC locking

f1

16.88MHz

PM

0.1rad

bKAGRA

Name

Frequency

Type

Mod. index

Relative Amplitude to Carrier before PRM

Oscillator Phase Noise

Oscillator Amplitude Noise

Comment

fIMC

13.78MHz

PM

JGW-T1605493

f1

16.880961MHz

PM

0.2rad (nominal 0.15)

BRSE, DRSE

BRSE, DRSE

f2

45.0159MHz

PM

0.1rad (nominal 0.05)

f3

56.2699MHz

AM

point of view0.05

Non-resonant sidebands to be used only for lock acquisition. Modulation index value, m, means the carrier field amplitude E0 (not power) is modulated by m*E0 (so, the sideband amplitude is m/2*E0; checked with Optickle). This SB is turned off once the interferometer is locked.

2*f3

112.5398MHz

AM

less than ??

Maximum permitted 2nd harmonics amplitude of f3-AM. To be calculated from the error signal availability during lock acquisition.

f1-AM

16.880961MHz

AM

65% of PM amplitude

Optional

fIMC

??? MHz

PM

0.025?

TBD (modulation depth written is from aLIGO value); JGW-T1605493

Assumed modulator arrangement

In the Optickle modeling, f1, f2 and f3 modulations are applied in series in this order. Optickle can properly handle the generation of sidebands on sidebands. So it is confirmed that series modulation is OK for bKAGRA. In practice, it may be better to apply f3 modulation first. This is to be discussed with IOO.

RFSB transmission servo

The RFSB frequencies (f1 and f2) should be set to maximize their power inside PRC, i.e. fully resonant in the central part of the interferometer. Therefore, at first, the MC length has to be adjusted to transmit the RFSBs optimized in frequency for the main interferometer. After the DC adjustment, however, small continuous adjustment to the RFSB frequencies to minimize the RFAM generation by the transmission through the MC should be performed by a RFSB transmission servo. Note that MIF does not require this servo to be implemented in the iKAGRA phase.