# Lock Acquisition

Lock acquisition scheme has to be planed carefully because it was a big problem in the first generation large-scale interferometers.

Probabilistic lock (a.k.a. lucky lock) won't probably work. Other locking schemes such as the arm pre-locking has to be considered.

## Auxiliary Lock System

Also known as green laser lock, this scheme will make use of auxiliary lasers to lock the arm cavities first.

## Purchase List

See here.

### Description of the blocks

#### Phase Comparison

• When you combine two beams with power P, we get the beat note with amplitude of 2 alpha P Sin phi, where alpha is the contrast (0~1) and phi is the relative phase between the fields. Thus, the phase sensitivity is 2 alpha P [W/rad]. e.g. Two 1mW beams geneartes 4mWpp beat if the contrast is 1. The slope is 0.002 alpha W/rad.

• For the broadband PD, InGaAs is not relevant because of the high junction capacitance. If we use Si PD (like FFD-100 phi=2.5mm), the responsivity is eta = 0.08 [A/W].

• BBPD Transimepedance and the shotnoise intercept current are assumed to be 1e3 [V/A] and 0.3 [mA], from the experience of LIGO BBPD.
• Total gain is 1 [V/rad] if we assume alpha and P to be 0.5 and 12.5mW respectively.

• Shot noise
• Shot noise of the modulated beam is described by <in^2> = 2 e [I0+1/2 dI Sin(phi)], according to N. Mio and K. Tsubono, Physics LettersA 164 (1992) 255-258.　Does nonstationary part cancel because of the orthogonality of the RF and LO signals???

• Consider only the stationary part, in = sqrt(2 e I0). Thus in/eta/(2 alpha P) = sqrt(e / eta / alpha / P) [rad/rtHz]. This corresponds to 2.5e-8 rad/rtHz.

#### Frequency noise of NPRO

• 1e4/f [Hz/rtHz] according to R. Adhikari's PhD thesis.

#### Shot noise

LCGT/subgroup/ifo/ISC/TaskList/LockAcquisition (last edited 2012-05-08 16:20:01 by YoichiAso)