frequency response of ligo interferometers andrew weber university of maryland (no relation) surf...
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Frequency Response of LIGO Interferometers
Andrew Weber University of Maryland (no relation)
SURF Student Lecture Series
Advisor: Andri Gretarsson
Introduction
To Investigate the Frequency Response of LIGO Interferometers Above the 1st FSR
•Analytically •Using the E2E model
To Describe the Angular Response Above the 1st FSR
Single Arm Fabry-Perot
Use this description for the transfer function and verify with E2E
From R. Schilling 1996
Transfer Function for Single Arm FP Cavity
Normalized Frequency
Res
pons
e
FP Cavity
• For LIGO 4 km IFO the second peak is centered about 37.5 kHz
Using the E2E Model
One 4 km FP Arm
Input:Swept Sine 0-90 kHz
Output:
Frequency Response of One Arm, 4 km IFO(E2E model)
Single 4 km FP Cavity in E2E
• 2nd Peak at 37.5 kHz Same as calculated above
Two Arm FP IFO 2 km
Two Arms Plus Recycling Cavity
• Swept Sine displacement to both
mirrors (differential mode)
Frequency Response of 2 Arm, 2 km IFO
(E2E model)
Peak at 75 kHz or at normalized frequency = 0.5
What Does This Mean?• This Shows that the sensitivity is restored again at
multiples of cavity FSR
• Suggests Search For GWs at Higher Frequencies
Might be Possible
However…
• What are the noise characteristics at high frequencies?
• Is it an interesting place to search?
Angular Response
Angle from x-y plane
Am
plit
ude
Am
plit
ude
1st Sensitivity Peak
2nd Sensitivity Peak
Angle from x-y plane
• Angular response at low frequencies is expected
• Angular Response high frequencies (37.5 kHz) has zeros at optimal orientation!
Angular Response
Angular Response of 1st and 2nd Sensitivity Peak
Further investigation
• Need to develop description of 2 arm model
• Should acquire noise profile at 37.5 kHz
Am
plit
ude
Angle from x-y axis
Earlier This Summer…
Purpose:
To suppress the 60 Hz (& higher multiples) power source noise from AS_Q to headphones.
“Twin T” Notch Filter