Frequency Comb Vernier spectroscopy Frequency Comb Vernier Spectroscopy

Frequency Comb Vernier spectroscopy 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, De. Boelelaan 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 1

Outline • Introduction: – Frequency combs and Optical resonators Frequency Comb Vernier Spectroscopy • XUV comb generation • Optical vernier spectroscopy • Outlook 'Metrology with Frequency Comb Lasers', 2007 2

'Metrology with Frequency Comb Lasers', 2007 3 Frequency Comb Vernier Spectroscopy Frequency combs and optical resonators

Frequency Combs E(t)=A(t)eiwct = S Am e-imwrt-iwct m=-¥ 1 n = n 1 r + 1 CE , 1 CE < 1 r, 7=2 1 CE/1 r 'Metrology with Frequency Comb Lasers', 2007 4 Frequency Comb Vernier Spectroscopy +¥

Example: Hydrogen Frequency Comb Vernier Spectroscopy f(1 S-2 S) = 2 466 061 102 474 851(34) Hz 'Metrology with Frequency Comb Lasers', 2007 5

Fabry perot resonators Frequency Comb Vernier Spectroscopy light source 'Metrology with Frequency Comb Lasers', 2007 6

… provide stable references • Narrow Markers in Frequency space Frequency Comb Vernier Spectroscopy – If high finesse • High stability – ~10 -15 @ 1 s – Hz linewidth @ 1 PHz – ~10 -16 m length stability 'Metrology with Frequency Comb Lasers', 2007 7

… enhance nonlinear conversion • Pc=F/ Frequency Comb Vernier Spectroscopy – Output power grows with finesse 2 or higher! • Example: – SHG 560 nm->280 nm – 900 m. W driving power – 20% conversion: 900 m. W->200 m. W 'Metrology with Frequency Comb Lasers', 2007 8

… enhance sensitivity • Cavity absorbtion spectroscopy Frequency Comb Vernier Spectroscopy – Increased interaction length – Intrinsically narrow band • Cavity ring down – Intrinsically robust – Can be broad band 'Metrology with Frequency Comb Lasers', 2007 9

Response function Frequency Comb Vernier Spectroscopy 'Metrology with Frequency Comb Lasers', 2007 Ca e nb m e h c at o dt FC 10

Cavity enhanced HHG – No dispersion • Electric field in the pulse envelope has to look the same for both pulses -> equidistant modespacing – frep = f. FSR • Timedelay between pulses = cavity roundtrip time – f. CEO matches • HHG inside the resonator 'Metrology with Frequency Comb Lasers', 2007 11 Frequency Comb Vernier Spectroscopy • Obvious requirements

XUV Output Circ. Power 40 W, intensity in the focus 5 x 1013 W/cm 2 Frequency Comb Vernier Spectroscopy C. Gohle et al. , Nature, 436, 234 (2005) R. J. Jones et al. , PRL, 94, 193201 (2005) 'Metrology with Frequency Comb Lasers', 2007 12

Coherence (of the 3 rd harm. ) Frequency Comb Vernier Spectroscopy C. Gohle et al. , Nature, 436, 234 (2005) R. J. Jones et al. , PRL, 94, 193201 (2005) 'Metrology with Frequency Comb Lasers', 2007 13

… coherence! Frequency Comb Vernier Spectroscopy (probably) 'Metrology with Frequency Comb Lasers', 2007 14

Possible Applications • Direct frequency comb spectroscopy in the XUV • 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 15 Frequency Comb Vernier Spectroscopy – It is cw, so no transients

'Metrology with Frequency Comb Lasers', 2007 16 Frequency Comb Vernier Spectroscopy

Direct comb spectroscopy, the good I(1) 300 THz 1 3, 000 narrow band modes with 0. 3 m. W power Simultaneously tuneable and referencable 1 Marian et al, PRL, 95, 023001 (2005)’ V. Gerginov et al. Optics Letters, 30, 1734 (2005) 'Metrology with Frequency Comb Lasers', 2007 17 Frequency Comb Vernier Spectroscopy 300 THz band width and 100 MHz mode spacing.

… and the bad • Large background • Aliasing – Spectra difficult to interpret • Small power per mode – Small signal – Nonlinear (dopplerfree) spectroscopy difficult 'Metrology with Frequency Comb Lasers', 2007 18 Frequency Comb Vernier Spectroscopy – for absorbtion measurements – Causing stark shifts

. . . the remedy Frequency Comb Vernier Spectroscopy 'Metrology with Frequency Comb Lasers', 2007 19

Data Single scan (10 ms) • Blue box: unique data • Red boxes: identified features • Gaussian PSF much larger than airy ! Brightness~Int egral of airy 20 Frequency Comb Vernier Spectroscopy 'Metrology with Frequency Comb Lasers', 2007 •

ar. Xiv: 0706. 1582 v 1 [physics. optics] O 2 magnetic dipole intercombinationline (760 nm) Frequency Comb Vernier Spectroscopy Red: HITRAN data 'Metrology with Frequency Comb Lasers', 2007 21

Results* Absorbtion: • Noisefloor O 2 A-Band Frequency Comb Vernier Spectroscopy < 10 -5/cm (100 Hz)1/2= < 10 -6/cm Hz 1/2 (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/Hz 1/2 * ar. Xiv: 0706. 1582 v 1 [physics. optics] ** Rothman, L. S. et al. , J. Quant. Spect. Rad. Trans. , 96, 139 -204 (2005) 'Metrology with Frequency Comb Lasers', 2007 22

… and the bad • Large background • Aliasing – Spectra difficult to interpret • Small power per mode – Small signal – Nonlinear (dopplerfree) spectroscopy difficult … may be possible 'Metrology with Frequency Comb Lasers', 2007 23 Frequency Comb Vernier Spectroscopy – for absorbtion measurements – Causing stark shifts … reduced

Thanks Akira Ozawa (fs-Cavities) Birgitta Bernhardt Jens Rauschenberger Theodor W. Hänsch Albert Schliesser Thomas Udem Funding: 'Metrology with Frequency Comb Lasers', 2007 24 Frequency Comb Vernier Spectroscopy Maximilian Herrmann (Ion Traps) Sebastian Knünz Valentin Batteiga (Hydrogen) Nikolai Kolachevski Janis Alnis Arthur Matveev Elisabeth Peters