Michelson Noise budget

• Some noise curves to be included
  • Shot Noise
  • Dark (RFPD) Noise
  • ADC Noise
  • Laser Amplitude noise
  • Laser Frequency Noise
  • Oscillator Noises
  • DAC Noise
  • Coil Driver Noise

Measurements

• 6/Mar/2012 by KK and KI

Sensor in use

• AS55_Q

  • Gain of whitening filter = 30 dB for both the I and Q.

  • Demodulation phase = 5.4 deg (at which the I signal doesn't respond to the Michelson displacement).

  • ~ very tiny DC light is on the RFPD

  
  

• Modulation Depths
  • Gamma_11 = 0.136
  • Gamma_55 = 0.157

DC light

• port name	DC power [mW]
  AS55	~0
  REFL	1.9 mW

Sidebands

• The values noted here were estimated from the OSAs at the AS and REFL ports.

Optical gains

• Parameters
  description	values	notes
  Estimated Optical gain	57.7 W/m
  Expected optical gain	47.03 W/m
  Measured pk-pk Michelson error signal	1000 counts	Michelson was freely swinging
  Raw optical gain	5.9052 x10^9 [counts/meter]	= 4 * pi / lambda * (half of pk-pk error signals)
  demod board gain	10	AS55 has a piggy back amplifier
  ADC conversion	1638.4 counts / V	16 bit, +/-20 V
  Trans impedance at 55 MHz	556.3 Ohm	AS55 characterization
  Responsibity of diodes	0.75 [A/W]	from the spec sheet of CS3102
  Attenuation in the AS path	0.99 * 0.5	There are two BSs in front of the AS55 RFPD

• Theoretically the MICH error signal can be derived by applying the following equation

  • 

Servo filters

• UGF = 55 Hz
• Only FM5 (10:1000) was activated.
• G = -2
• No limiter in the digital path.
• Feeding the signal back to BS.
• Dewhitening filters in BS are ON.
• Assumption : BS actuator has a pole at 1 Hz with Q = 5
• Time delay = (without considering the effects from the analog circuits and the down sampleing filters.)

RAM effects

• There is a big RAM signal in the I signal. The signals float from -100 counts to 0 counts as the Michelson freely swings.
  • The amount of the RAM looks changing as a function of time.
• The Q signal looks having not so much RAM effect.
• The highest value seems to be always ~ 0, while the lowest value varies as a function of time. It went to -200 counts some times.