Advances on Portable Frequency Advances on Portable Frequency References in LUMOS References in LUMOS Kansas State University Kansas State University Kevin Knabe Kevin Knabe Advising Professors: Kristan Corwin & Brian Washburn Advising Professors: Kristan Corwin & Brian Washburn Colleagues: Rajesh Thapa, Andrew Jones, Aaron Pung, Asma Al- Colleagues: Rajesh Thapa, Andrew Jones, Aaron Pung, Asma Al- Rawhi Rawhi
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Advances on Portable Frequency References in LUMOS
Advances on Portable Frequency References in LUMOS. Kansas State University Kevin Knabe. Advising Professors: Kristan Corwin & Brian Washburn Colleagues: Rajesh Thapa, Andrew Jones, Aaron Pung, Asma Al-Rawhi. Outline. Goals Overview of Frequency Standards Saturated Absorption Spectroscopy - PowerPoint PPT Presentation
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Advances on Portable Frequency Advances on Portable Frequency References in LUMOSReferences in LUMOS
Kansas State UniversityKansas State UniversityKevin KnabeKevin Knabe
Advising Professors: Kristan Corwin & Brian WashburnAdvising Professors: Kristan Corwin & Brian WashburnColleagues: Rajesh Thapa, Andrew Jones, Aaron Pung, Asma Al-RawhiColleagues: Rajesh Thapa, Andrew Jones, Aaron Pung, Asma Al-Rawhi
OutlineOutline
GoalsGoals Overview of Frequency StandardsOverview of Frequency Standards Saturated Absorption SpectroscopySaturated Absorption Spectroscopy Fiber CellsFiber Cells Reflected Pump Setup (single Reflected Pump Setup (single
beam!)beam!) LockingLocking Update on the Cr:F LaserUpdate on the Cr:F Laser
GoalsGoals
Studying Studying νν11 + + νν33 vibrational band vibrational band of acetylene (optimize signal for of acetylene (optimize signal for locking)locking)
Create an acetylene cell using Create an acetylene cell using PPhotonic hotonic BBandandGGap (PBG) Fiber ap (PBG) Fiber and and SSingle ingle MMode ode FFiber (SMF)iber (SMF)
Lock a laser to absorption signalLock a laser to absorption signal
Acetylene as Frequency Acetylene as Frequency ReferenceReference
R. Thapa, K. Knabe, M. Faheem, A. Naweed, O. L. Weaver, and K. L. Corwin, "Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber," Opt. Lett. 31, 2489 (2006).
20 μm fiber shows lower fundamental width at zero pressure – larger transit time, so less broadening!
Mode field radius of
fiber
Power ResultsPower Results
Power broadening widens transition, but discrimination keeps going up
Because of availability of additional laser sources, staying under 50 mW may be a requirement (EDFA’s are expensive)
0 20 40 60 80 1000.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
D (
khz-1
)
Power (mW)
GoalsGoals
Studying Studying νν11 + + νν33 vibrational band vibrational band of acetylene (optimize signal for of acetylene (optimize signal for locking)locking)
Create an acetylene cell using Create an acetylene cell using PPhotonic hotonic BBandandGGap (PBG) Fiber ap (PBG) Fiber and and SSingle ingle MMode ode FFiber (SMF)iber (SMF)
Lock a laser to absorption signalLock a laser to absorption signal
“Arc fusion splicing of hollow-core photonic bandgap fibers for gas-filled fiber cells”R. Thapa, K. L. Corwin, and B. R. Washburn, Accepted to Optics Express 2006
LUMOS Spliced Fiber (2005) - 20 μm core
Splice Loss:PBG ->SMF ~ 2.0 dB (30%)SMF ->PBG ~ 0.5 dB (10%)
The Splice is RightThe Splice is Right
20 μm core PBG supports more than 1 mode!
“Half Cell”
Making Fiber CellsMaking Fiber Cells
SMFPBGSMF
Vacuum Chamber filled to a low
pressure with C2H2
CO2 Laser
Arc Fusion Splicer
We will have a robust portable fiber cell!Aaron
Pung
GoalsGoals
Studying Studying νν11 + + νν33 vibrational band vibrational band of acetylene (optimize signal for of acetylene (optimize signal for locking)locking)
Create an acetylene cell using Create an acetylene cell using PPhotonic hotonic BBandandGGap (PBG) Fiber and ap (PBG) Fiber and SSingle ingle MMode ode FFiber (SMF)iber (SMF)
New GoalNew Goal: Check quality of half : Check quality of half cellscells
Lock a laser to absorption signalLock a laser to absorption signal
Saturated Saturated Absorption Absorption
Spectroscopy With Spectroscopy With Only 1 Beam in PBG Only 1 Beam in PBG
Fiber*Fiber*
*Patent pending
ECDL EDFA EDFA
PC
PBGF
PBS PBS 2
λ
PD
Iso .
Diagnostics
VC 4
λ
2
λ
SMF
Splice
2x AOM
Pump-Probe Setup for Pump-Probe Setup for Spliced Half-CellsSpliced Half-Cells
High Loss
Low Loss
Pump
Probe
-800 -600 -400 -200 0 200 400 600 800
0.0
0.2
0.4
0.6
0.8
Ab
sorp
tio
n (
Arb
. u
nit
s)
Frequency Offset (MHz)
P11 line at 0.9 torr, 23 mW pump power
Pump-Probe Setup for Pump-Probe Setup for Spliced Half-Cells – No Spliced Half-Cells – No
AOMAOM
ECDL EDFA EDFA
PC
PBGF
PBS PBS 2
λ
PD
Iso .
Diagnostics
VC 4
λ
2
λ
SMF
Splice
-500 0 500
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Frequency Offset (MHz)
High Loss
Low Loss
Pump
Probe
ECDL EDFA
PBGF
BS 2λ
PD
40%
60%
Diagnostics
VC SMF
Splice
Reflected Pump SetupReflected Pump Setup
Pump
Probe
-500 0 500
0.0
0.1
0.2
0.3
0.4
0.5
0.6
*L
(Arb
. Uni
ts)
Frequency Offset (MHz)
R-Pump Results: R-Pump Results: Signal QualitySignal Quality
-1000 -500 0 500 1000
0.0
0.2
0.4
0.6
0.8
*L
(uni
tless
)
Frequency (MHz)
0.31 t 0.39 t 0.45 t 0.50 t 0.55 t 0.66 t
Keeping saturated absorption feature centered with Doppler broadened profile has locking benefits
Wings exhibit very small interference pattern which has a free spectral range associated with the length of the PBG fiber
Reflections occurring at front end of splice, causing interference
R-Pump Results: R-Pump Results: Comparison Of WidthsComparison Of Widths
R-Pump : P11 Line : Pump Power = 30 mW
Pump-Probe : P11 Line : Pump Power = 29 mW
0.00 0.25 0.50 0.75 1.00
20
25
30
35
L (M
Hz)
Pressure (torr)
R-Pump : P11 Line : Pressure = 0.5 torr
Pump-Probe : P11 Line : Pressure = 1 torr
0 25 50 75 100
25
30
35
40
45
L (M
Hz)
Power (mW)
GoalsGoals
Studying Studying νν11 + + νν33 vibrational band of vibrational band of acetylene (optimize signal for acetylene (optimize signal for locking)locking)
Create an acetylene cell using Create an acetylene cell using PPhotonic hotonic BBandandGGap (PBG) Fiber and ap (PBG) Fiber and SSingle ingle MMode ode FFiber (SMF)iber (SMF)
Check quality of half cellsCheck quality of half cells Lock a laser to absorption signal, Lock a laser to absorption signal,
then compare with locked Cr:F then compare with locked Cr:F frequency combfrequency comb
LockingLocking
– Lock laser to sat. abs feature.Lock laser to sat. abs feature.– Measure with comb referenced to GPS.Measure with comb referenced to GPS.– Lock comb to fiber-based reference, output Lock comb to fiber-based reference, output