1. Cavity-Enhanced Direct Frequency Comb Velocity Modulation Spectroscopy Laura Sinclair William Ames, Tyler Coffey, Kevin Cossel Jun Ye and Eric Cornell Funding: NSF and the W.M. Keck Foundation

2. Advantages of Combining Cavity-Enhanced Direct Frequency Comb Spectroscopy with Velocity Modulation Spectroscopy  Broad Simultaneous Bandwidth -- Massively Parallel Data Collection  Spectral resolution limited by width of single comb tooth  Absolute frequency accuracy of better than 30 MHz  Sensitivity to 1 ppm fractional absorption and suppression of neutral signals For more on CE-DFCS, see F. Adler, M.J. Thorpe, K.C. Cossel, J. Ye, Annu. Rev. Anal. Chem. 3 175 (2010) For more on VMS, see S.K. Stephenson, R.J. Saykally, Chem. Rev. 105 3220 (2005)

3. Survey Spectroscopy of Molecular Ions  Necessary for the JILA electron Electric Dipole Moment (eEDM) experiment explain eEDM  Molecular Ions are important for astrochemistry and tests of fundamental physics

4. Survey Spectroscopy of Molecular Ions for the JILA eEDM Experiment Predicted HfF+ Structure [2],[3]  3  1 metastable state of HfF+ and ThF+ is potential “science state” for eEDM search [1]  Use multiple excited states for state preparation and spin readout  Very little spectroscopic data exists for either species [1] E. Meyer, J. Bohn, M. Deskevich, Phys. Rev. A 73 n6, 062108 (2006) [2] A. Petrov, N. Mosyagin, T. Isaev, A. Titov, Phys. Rev. A 76 030501 (R) (2007) [3] A. Petrov, N. Mosyagin, A. Titov, Phys. Rev. A 79 012505 (2009)

5. Velocity Modulation Spectroscopy: HfF+ 550 C ~ - + + - ++ Wavelength [cm -1 ]

6. Velocity Modulation Spectroscopy: HfF+ - + + - ++

7. Frequency combs Frequency combs provide narrow lines over a wide spectral bandwidth. Only two parameters ( and ) define the comb!

8. Cavity-Enhanced Direct Frequency Comb Spectroscopy... Frequency Cavity free spectral range

9. Cavity-Enhanced Direct Frequency Comb Spectroscopy... Frequency f rep f n = f 0 + f rep

10. Our System ~ 1 m 10 kHz ~ 200 mA ~ ~

11. Our System ~ ~ Bi-Directional Ring Cavity Finesse ~ 100 FSR ~ 120 MHz

12. Our System ~ ~ 3GHz Frequency Comb + Reference CW Ti:Saph

13. 2D Frequency Dispersed Imaging System Our System ~ ~ Lock-in Detection on MANY parallel channels

14. Coupling the Comb into the Science Cavity Science Cavity Length ~ 2.5 m Free Spectral Range ~ 120 MHz Finesse ~ 100 Science Cavity Linewidth ~ 1 MHz …… Cavity FSR mm+25 frep (~ 3GHz) m+50 f = n*frep + f0 f = (n+1)*frep + f0 f = (n+2)*frep + f0

15. Coupling the Comb into the Science Cavity

16. 2D-Frequency Dispersed Lock-in Imaging [1] [1] S. Beer, P. Seitz, Research in Microelectronics and Electronics, 2005 PhD, 2 135 (2005) Heliotis

17. VIPA Etalon Direction Grating Direction 2D-Frequency Dispersed Lock-in Imaging

18. VIPA Etalon Direction Grating Direction 1300 Channels of Lock-in Detection ! 2D-Frequency Dispersed Lock-in Imaging

19. VIPA Etalon Direction Grating Direction 2D-Frequency Dispersed Lock-in Imaging Each Individual Comb Tooth Resolved ~3 GHz ~100 GHz

20. Or PBS Test of Technique with N2+ and CW Ti:Saph “Single Comb Tooth”

21. Test of Technique with N2+ and CW Ti:Saph [1] [1] A 2  -> X 2  (4,2) band molecular constants given by D. Collet et al. Chem. Phys., 286 311 (1998)

22. Or PBS Test of Technique with N2+ and CW Ti:Saph Using 2D-Frequency Dispersed Lock-in Imaging “Single Comb Tooth”

23. Test of Technique with N2+ and CW Ti:Saph Using 2D-Frequency Dispersed Lock-in Imaging

28. Conclusions  Cavity-Enhanced Direct Frequency Comb Velocity Modulation Spectroscopy provides ion sensitive detection with broad simultaneous bandwidth and high spectral resolution  2D lock-in imaging system allows for 1300 channels of lock-in detection  High absolute frequency accuracy across the full bandwidth  Cavity enhancement increases sensitivity and subtraction of counter-propagating beams reduces common mode noise and increases rejection of neutrals  Technique tested with A 2  u –X 2  + g (4,2) N2+ band

29. Extra slides follow

30. Velocity Modulation Spectroscopy: HfF+ R: J”=J’-1 Q: J”=J’ P: J”=J’+1 P(1) line missing 1  +  3  1 (0,0) R(0) and Q(1) lines present Transition is  ”=0   ’=1

31. Velocity Modulation Spectroscopy: HfF + Results of Fit offset = 13002.229 +/- 0.003 cm -1 B’ = 0.28117 +/- 0.0001 cm -1 D’ = 1x10 -7 +/- 1x10 -7 cm -1 k’ = (3.55 +/- 0.02) x 10 -4 cm -1 Rotational Energies: Upper State: F(J’) = (B’-P*(k/2))*J’(J’+1) – D’ J’ 2 (J’+1) 2 Lower State: F(J”) = B”*J”(J”+1) – D”J” 2 (J”+1) 2 Energy of a given transition= h offset + F(J’) – F(J”) Parity P=1,  J=+/- 1 P=-1,  J=0  -doubling term B” = 0.30489 +/- 0.0001 cm -1 D” = 1x10 -7 +/- 1x10 -7 cm -1 1 cm -1 = 30 GHz and at 780nm, 1 cm -1 ~ 0.06 nm Coupling of electron’s angular momentum and rotation 1  +  3  1 (0,0)