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Transcript of Tunable Laser Spectroscopy Referenced with Dual Frequency Combs International Symposium on Molecular...
![Page 1: Tunable Laser Spectroscopy Referenced with Dual Frequency Combs International Symposium on Molecular Spectroscopy 2010 Fabrizio Giorgetta, Ian Coddington,](https://reader030.fdocuments.us/reader030/viewer/2022033022/56649ce45503460f949b1650/html5/thumbnails/1.jpg)
Tunable Laser Spectroscopy Referenced with Dual Frequency Combs
International Symposium on Molecular Spectroscopy 2010
Fabrizio Giorgetta, Ian Coddington, Esther Baumann, William Swann, Nathan Newbury
NIST, Boulder, CO
![Page 2: Tunable Laser Spectroscopy Referenced with Dual Frequency Combs International Symposium on Molecular Spectroscopy 2010 Fabrizio Giorgetta, Ian Coddington,](https://reader030.fdocuments.us/reader030/viewer/2022033022/56649ce45503460f949b1650/html5/thumbnails/2.jpg)
Introduction• Motivation: calibrated, fast, broadband, and sensitive spectroscopy
• Tunable laser spectroscopy– Highly sensitive
– Broadband measurement
– ‘Jump’ between spectral regions of interest
• Dual comb spectroscopy– High frequency accuracy
– Broadband measurement
• Combine both for– High sensitivity
– Broadband measurement
– High frequency accuracy
Gas
cell
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Measuring rapidly tuned cw lasers• Goal: measure instantaneous laser frequency spectrum
– Accuracy & resolution = instantaneous laser linewidth
• Conventional OSA, FTIRs: inadequate resolution, accuracy, and speed
• Comb assisted diode laser spectroscopy [Del’Haye et al., Nat. Phot. 3, 529 (2009)]– Highly linear frequency sweep with MHz resolution– Significant improvement over etalon techniques, but– Only works with continuously tuned lasers
• Dual comb spectroscopy of dynamic laser– Absolute frequency accuracy of a referenced frequency comb– Frequency resolution can be time-bandwidth limited– Fast update times (down to 30 μs demonstrated)– Can support arbitrary cw waveforms– Works with frequency-switchable lasers (MG-Y, SG-DBR)
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(fr)-1
J.-L. Peng et al. Appl. Phys. B 92, 513 (2008).Coddington et al. Phys. Rev. Lett. 100, 013902 (2008)Wideband
Intensity Measurement
- Resolution: fr (100 MHz)
- Accuracy: ~ 1 kHz
- Update: TU = 1/ fr (300 μs)
- Span: 1/ (2T)=TU fr2/2
(1.5 THz)
Dynamic cw laser
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fr+f ~ 100 MHz + 3 kHz
ELO
Tight phase locking of both combsRequire residual linewidth << Δf (3 kHz):
• Phase lock combs to two cw lasers– For high frequency accuracy, lock cw lasers to cavity
• Achieves sub-radians optical coherence
fr ~ 100 MHz
Esignal
1535 nm1560 nmCavity stabilized Lasers
frequency
field
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High Resolution Measurement
cw
TU : 300 μs
Dynamic cw laser
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Instantaneous optical frequency
Instantaneous frequencyon fast time scale
Inst freq. FFT
TimeVol
tage
~ f
ield
Frequency
Inte
nsity
Frequency domain comb picture Measured data
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Frequency Measurement of Tuned Laser
Measurements mutually independent
Arbitrary / discontinuous waveforms
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Gas Spectroscopy with a Step-tuned Laser
• Step-tune laser frequency– Fine steps across line– One coarse step between lines
• Frequency comb accuracy• Span: 5.2 THz (42 nm)
AD
CDynamic cw laser
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Gas Spectroscopy
• Total measurement time: ~ 5 s (limited by cw laser)• Frequency axis accuracy ~ 1 kHz• Line center frequency accuracy ~ 1 MHz (fit residual)
HiTran data
CO(115 Torr)
CO2
(1000 Torr)C2H2
(50 Torr)
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Conclusion• Demonstrated coherent dual-comb spectroscopy of tunable cw laser
– High frequency resolution (3 kHz) and accuracy (~1 kHz)
– High time resolution (down to TU = 30 μs)
– Minimal a priori frequency knowledge required: 3 THz for TU = 300 μs
• Future improvements– Higher comb repetition rate to track faster lasers
– Other spectral regions
– Real-time processing
• Applications– Metrology of lasers with fast frequency tuning / hopping
– Dynamic, wide band optical sensing
Thank you
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Frequency combsT. W. Hänsch, Rev. Mod. Phys. 78, 1297 (2006).
J. L. Hall, Rev. Mod. Phys. 78, 1279 (2006).
Stabilization of any two degrees of freedom → Entire comb stabilized→ Entire pulse train stabilized
t
1/frepetition
offset
PassivelyMode-locked LaserTi:sapphireCr:forsteriteEr FiberYb fiber…
fcw=fbeat+ fceo + N fr
cw
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Data II
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Instantaneous optical frequency
Instantaneous frequencyon fast time scale
Inst.freq
FFTTime
Fie
ld