1. High resolution spectroscopy with a femtosecond laser frequency comb
Vladislav Gerginov1
Scott Diddams2, Albrecht Bartels3, Carol E. Tanner1 and Leo Hollberg2
1Department of physics, University of Notre Dame, Notre Dame, IN 46556
2National Institute of Standards and Technology, 325 Broadway M.S. 847, Boulder, CO 80305
3Gigaoptics GmbH (see exhibit)

2. Pulsed laser spectroscopy
1970s: Ideas of 2-photon spectroscopy with pulsed sources from T. W. Hänsch and
V. P. Chebotaev;
“Narrow resonances of two-photon absorption of super-narrow pulses in a gas”
Y. V. Baklanov and V. P. Chebotaev, Appl. Phys. 12, 97 (1977).
“Coherent Two-Photon Excitation by Multiple Light Pulses” R. Teets, J. Eckstein, and T. W. Hänsch Phys. Rev. Lett. 38, (1977).
“Two-photon spectroscopy of laser-cooled Rb using a mode-locked laser”,
M. J. Snadden, A. S. Bell, E. Riis, A. I. Ferguson,
Opt. Commun, 125, 70-76, (1996).
“High sensitivity phase spectroscopy with picosecond resolution”
J. –C. Diels, B. Atherton, S. Diddams; Proceedings of 5th European Quantum Electronics Conference, 29 195–195, (1994).
“United Time-Frequency Spectroscopy for Dynamics and Global Structure”,
A. Marian, M. C. Stowe, J. R. Lawall, D. Felinto, J. Ye, Science Express, , 2004.

3. Direct single-photon spectroscopy using a femtosecond laser
Bartels et al., Opt. Lett. 27(20) 1839, 2002
Bartels et al., Opt. Lett. 29,10,1081,2004

4. 133Cs energy diagram and
FLFC output spectrum

5. Optical frequency measurements
Experimental setup
Optical frequency measurements

6. D1 14nW power
D2 1.5 nW power

7. D1 line measurements F-F’ Previous1 (kHz) This work (kHz)
Difference (kHz)
F3-F3
(4.9)
(85.0)
-6.0 ( 0.1 sigma)
F3-F4
(5.3)
(16.4)
17.6 (1 sigma)
F4-F3
(4.6)
(10.5)
16.1 (1.4 sigma)
F4-F4
(4.0)
(28.0)
7.8 ( 0.3 sigma)
1V. Gerginov, K. Calkins, C. E. Tanner, A. Bartels,
J. McFerran, S. Diddams, L. Hollberg, in preparation

8. D2 line measurements F-F’ Previous1 (kHz) This work (kHz)
Difference (kHz)
F3-F2
(5.5)
(9.7)
-5.2 (0.5 sigma)
F3-F3
(5.5)
(98.5)
-79.8(0.8 sigma)
F3-F4
(5.6)
(34.2)
-16.3 (0.5 sigma)
F4-F3
(5.5)
(21.7)
-15.4 (0.7 sigma)
F4-F4
(5.5)
(167.8)
-25.3( 0.2 sigma)
F4-F5
(5.5)
(4.5)
-22.2( 3 sigma)
1V. Gerginov, C. E. Tanner, S. Diddams, A. Bartels, L. Hollberg, PRA 70, , 2004

9. Cs D2 line optical clock  
Experimental setup
Cs D2 line optical clock  

10. Cs D2 line optical clock performance

11. Conclusions
Optical frequency measurements using a single comb component;
A stable array of optical and microwave frequencies;
Potential for femtosecond-laser based optical clocks;

12. Typical optical references performance
Typical optical frequency reference uncertainties:
This system: 852nm (1.7×10-10)
I2 stabilized He-Ne laser: nm (2.5×10-11)
I2 stabilized SHG of Nd:YAG: nm (9×10-12)
Rb 2-photon stabilized diode laser: nm (1.2×10-11)
GPS: <1kHz with 1-2 days of averaging

13. Conclusions
One-photon high resolution spectroscopy using the output of a femtosecond laser;
Optical frequency measurements with accuracy better than 100kHz, reaches below 10 kHz;
SubDoppler spectroscopy with 1nW laser power;
Optical and microwave output with absolute accuracy at level;
Potential for femtosecond-laser based optical clocks.

14. Doppler shift compensation

15. D2 line excitation