metrology with frequency comb lasers', 2007 frequency comb vernier spectroscopy 1 frequency...
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'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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Outline• Introduction:
– Frequency combs and Optical resonators
• XUV comb generation
• Optical vernier spectroscopy
• Outlook
'Metrology with Frequency Comb Lasers', 2007
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Frequency combs and optical resonators
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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Example: Hydrogen
f(1S-2S) = 2 466 061 102 474 851(34) Hz
'Metrology with Frequency Comb Lasers', 2007
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Fabry perot resonators
light source
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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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 ¡F¼
A
'Metrology with Frequency Comb Lasers', 2007
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Response function
Can be matched to FC
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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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)
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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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!
'Metrology with Frequency Comb Lasers', 2007
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Frequency Comb Vernier Spectroscopy
'Metrology with Frequency Comb Lasers', 2007
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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
'Metrology with Frequency Comb Lasers', 2007
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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