Metrology with Frequency Comb Lasers', 2007 Frequency Comb Vernier Spectroscopy 1 Frequency Comb Vernier spectroscopy C. Gohle, A. Renault, D.Z. Kandula,

'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


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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 ¡F¼

A


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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

Documents

Metrology with Frequency Comb Lasers', 2007 Frequency Comb Vernier Spectroscopy 1 Frequency Comb Vernier spectroscopy C. Gohle, A. Renault, D.Z. Kandula,