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'Metrology with Frequency Comb Lasers', 2007
Frequency Comb Vernier Spectroscopy
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Frequency Comb Vernier spectroscopy
C. Gohle, A. Renault, D.Z. Kandula, A.L. Wolf, W. Ubachs, K.S.E. Eikema
Laser Centre, Vrije Universiteit Amsterdam, DeBoelelaan 1081, 1081 HV Amsterdam
A. Ozawa, B. Bernhardt, B. Stein, A. Schliesser, Th. Udem, T.W. Hänsch
Max-Planck-Institut für Quantenoptik, Hans-Kopfermannstraße 1, 85748 Garching
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Outline• Introduction:
– Frequency combs and Optical resonators
• XUV comb generation
• Optical vernier spectroscopy
• Outlook
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Frequency combs and optical resonators
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Frequency Combs
E(t)=A(t)eict = +
m=- Am e-imrt-ict
1n = n1r + 1CE , 1CE < 1r, 7=2 1CE/1r
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Example: Hydrogen
f(1S-2S) = 2 466 061 102 474 851(34) Hz
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Fabry perot resonators
light source
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… provide stable references• Narrow Markers in
Frequency space– If high finesse
• High stability– ~10-15 @ 1 s– Hz linewidth @ 1 PHz– ~10-16m length
stability
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… enhance nonlinear conversion
• Pc=F/– Output power grows
with finesse2 or higher!
• Example:– SHG 560nm->280nm– 900mW driving power
– 20% conversion: 900mW->200mW
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… enhance sensitivity• Cavity absorbtion
spectroscopy– Increased
interaction length– Intrinsically narrow
band
• Cavity ring down– Intrinsically robust– Can be broad band
/ ¡ r
T ¡ F¼A
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Response function
Can be matched to FC
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Cavity enhanced HHG
• Obvious requirements– No dispersion
• Electric field in the pulse envelope has to look the same for both pulses -> equidistant modespacing
– frep = fFSR• Timedelay between pulses = cavity roundtrip time
– fCEO matches• HHG inside the resonator
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XUV Output
C. Gohle et al., Nature, 436, 234 (2005)R. J. Jones et al., PRL, 94, 193201 (2005)
Circ. Power 40W, intensity in the focus 5 x 1013 W/cm2
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Coherence (of the 3rd harm.)
C. Gohle et al., Nature, 436, 234 (2005)R. J. Jones et al., PRL, 94, 193201 (2005)
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… coherence!
(probably)
f
I (f )
f
log [I (f ) ]I (f )
f
high harmonic radiation frequency comb
odd harmonics
plateau
cut-off
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Possible Applications• Direct frequency comb spectroscopy in the
XUV– It is cw, so no transients
• Compact coherent XUV source for interferometry
• High repetition rate high intensity source for coincidence measurements
• BUT: power still low!• And many technical problems
• Use an amplifier!
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Frequency Comb Vernier Spectroscopy
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Direct comb spectroscopy, the good
300 THz
I(1)
1
300 THz band width and 100 MHz mode
spacing.
3,000,000 narrow band modes with 0.3 W power
1
Simultaneously tuneable and referencable
Marian et al, PRL, 95, 023001 (2005)’V.Gerginov et al. Optics Letters, 30, 1734 (2005)
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… and the bad• Large background
– for absorbtion measurements– Causing stark shifts
• Aliasing– Spectra difficult to interpret
• Small power per mode– Small signal– Nonlinear (dopplerfree) spectroscopy
difficult
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... the remedy
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Data• Single scan
(10ms)
• Blue box: unique data
• Red boxes: identified features
• Gaussian PSF much larger than airy ! Brightness~Integral of airy
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Red:HITRAN data
O2 magnetic dipole intercombinationline (760nm)arXiv:0706.1582v1 [physics.optics]
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Results*Absorbtion:•Noisefloor < 10-5/cm (100 Hz)1/2= < 10-6/cm Hz1/2 (shotnoise: <10-8)•> 4 THz bandwidth 1 GHz sampling (>4000 res. Datapoints in 10 ms)•Quantitative agreement in Amplitude and Frequency to HITRAN** database
Phase:- agrees with expectations (disp. features)-not optimized for good phase sensitivity-Still <0.1 mrad/Hz1/2
* arXiv:0706.1582v1 [physics.optics]** Rothman, L. S. et al., J. Quant. Spect. Rad. Trans., 96, 139-204 (2005)
O2 A-Band
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… and the bad• Large background
– for absorbtion measurements– Causing stark shifts
• Aliasing– Spectra difficult to interpret
• Small power per mode– Small signal– Nonlinear (dopplerfree) spectroscopy
difficult … may be possible
… reduced
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Thanks
Maximilian Herrmann(Ion Traps)Sebastian KnünzValentin Batteiga
Albert Schliesser
Akira Ozawa(fs-Cavities)Birgitta BernhardtJens Rauschenberger
Thomas Udem
Theodor W. Hänsch
Funding:
(Hydrogen)Nikolai KolachevskiJanis AlnisArthur MatveevElisabeth Peters