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pykat
Commits
dc607288
Commit
dc607288
authored
May 24, 2019
by
Phil Jones
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Adding function for filter cavity optimisation.
parent
f6256af2
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pykat/tools/filter_cavity.py
pykat/tools/filter_cavity.py
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pykat/tools/filter_cavity.py
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dc607288
import
numpy
as
np
def
filter_cavity_parameters
(
P
,
lambda0
,
m
,
Titm
,
Tsrm
,
L
,
loss
=
0
):
"""
Compute the optimal filter cavity detuning phase and input mirror
transmissivity for frequency-dependent squeezing in a tuned, dual-recycled
interferometer.
P - Arm cavity circulating power [W]
lambda0 - main laser wavelength [m]
m - mass of test masses (mirrors) [kg]
Titm - Power transmissivity of input test mass
Tsrm - Power transmissivity of signal recycling mirror
L - Filter cavity length [m]
loss - Filter cavity round-trip power loss
See Kwee et al. `Decoherence and degradation of squeezed states in
quantum filter cavities` Physical Review D, 2014, 90, 062006
"""
c
=
299792458.0
w0
=
2
*
np
.
pi
*
c
/
lambda0
FSR
=
c
/
(
2.0
*
L
)
# Approximate frequency at which IFO reaches SQL
# (i.e. radiation pressure noise = shot noise)
w_sql_0
=
8
/
c
*
np
.
sqrt
(
P
*
w0
/
(
m
*
Titm
))
w_sql
=
np
.
sqrt
(
Tsrm
)
/
(
1
+
np
.
sqrt
(
1
-
Tsrm
))
*
w_sql_0
if
loss
>
0
:
epsilon
=
4
/
(
2
+
np
.
sqrt
(
2
+
2
*
np
.
sqrt
(
1
+
(
2
*
w_sql
/
(
FSR
*
loss
))
**
4
))
)
else
:
epsilon
=
0
# Filter cavity bandwidth
gamma_f
=
(
np
.
sqrt
(
2
/
((
2
-
epsilon
)
*
np
.
sqrt
(
1
-
epsilon
)))
*
w_sql
/
(
2
*
np
.
pi
*
np
.
sqrt
(
2
))
)
# Detuning
delta
=
np
.
sqrt
(
1
-
epsilon
)
*
gamma_f
phi
=
-
delta
/
FSR
*
180.0
T
=
2.0
*
gamma_f
/
FSR
*
2
*
np
.
pi
return
phi
,
T
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