1. Institute of Atomic and Molecular Science, IAMS, Taiwan, ROC Wang-Yau Cheng, Chien-Ming Wu, Tz-Wei Liu and Yo-Huan Chen Progressive report on portable Ti:sapphire comb laser based on cesium-stabilized diode lasers

2. Chemistry laboratory Hubble observatory Keck observatory Hard to incorporate VIS-UV comb laser into 。。。

3. Ti:sapphire laser  most popular comb laser light source from NIR to UV Difficulties for being conveyable Conventionally, extending comb spectrum or 1f-2f interferometer is needed Inconvenient pump laser Mode frequency is actually not accurate enough and also sensitive to the environments LOCKED Self-reference m~10 6 When  ~2 mHz instability  f m ~ 2 kHz instability Directly referring  and f m to narrow atomic two-photon transitions

4. I(f) f  F=4 6 P 6 S F=3 6 D 8S 822 nm 884 nm 822 nm 884 nm 822 nm 884 nm A project locking all comb laser parameters by cesium cells Accuracy, comb-based CPT Opt. lett. 32, 563 (2007) Apply Physics B 92, 13-18 (2008) submitted

5. -12 -11  (sec, log) 30 MHz day Beat note (kHz) 05101520 -2 0 1 012 -13 off lock P+A P Allan deviation: 4*10 -13 ~150 Hz frequency uncertainty 822 nm optical frequency reference Opt. lett. 32, 563 (2007)

6. To PMT Cs cell PZT 17 cm 30 MHz 6S  8S F=3  F=3 Cs spectrometer Extended-cavity diode laser Paper submitted

7. 6S 1/2  6D 5/2 ;F=4~f’=6-2 6S 1/2  6D 5/2 ;F=3~f’=5-1 6S 1/2  6D 3/2 ;F=4~f’=2-5 6S 1/2  6D 3/2 ;F=3~f’=2-5 20 MHz 884 nm optical frequency reference

8. f  Difficulties: How to referring comb laser repetition rate directly to atomic spectrum

9. Population coherence between a and c states is thus built up Cesium Ground state hyperfine splitting  Clock frequency Coherent population trapping

10. Cesium Ground state hyperfine splitting  Clock frequency CPT signal by comb laser is extremely sensitive to repetition rate

12. Summary main marker from 884nm laser scale: Cmob-CPT clock Paper submitted 6S 1/2  6D 5/2 ;F=4~f’=6-2 6S 1/2  6D 5/2 ;F=3~f’=5-1 6S 1/2  6D 3/2 ;F=4~f’=2-5 6S 1/2  6D 3/2 ;F=3~f’=2-5 main marker from 822 nm laser Opt. lett. 32, 563 (2007) 30 MHz 6S  8S F=3  F=3 30ms time constant Cs spectrometer 1. no 1f-2f scheme 2. all comb parameters referring to atomic cesium transitions

13. On going works

14. 170 mm portable comb clock is now under construction 1. stable and small reference laser 3. small pump laser 2. small Ti:sapphire laser criteria: fiber laser + waveguide crystal + Optics letters 34, 1561 (2009) 10*30 mm

15. AOM2 Ti:S laser #1 Ti:S laser #2 532 nm Pump laser Second harmonic crystal Color filter Interference filter C 3 Molecule Mirrors in UV AOM1 PZT Signal reference Low noise detector (D1) Low noise detector (D2) Multi-heterodyne comb laser spectroscopy (Collaborate with Dr. Yen-Chu Hsu’s group ) Reference:NIST, PRL 100, 013902 (2008)

16. With C3 molecules– UV comb references

17. Gergly Cs MOTHand-size laser 宥寰 822 nm standard 子維 comb laser 建宏 建明 宗翰 852 nm CPT 芝佑 聖輝 彥龍 theory modeling 郁菁 建中 884 nm spectra 麗晶 It is a team work ! Acknowledge the funding support from NSC, Taiwan NSC94-2112-m-001-022- MY3

18. Cesium ground state become mixed state The wavefunction of mixed state will decay with a quantum beat (clock frequency) When the phase of repetition rate matches the phase of this quantum beat, a stable mixed state or ground-state coherence will then be built up Periodic-driven swing

20. Thanks for your attention

21. Our laser is uniquely suited for coherent multi-photon process  f n =n  -    I(f) f   f n = n  Apply Physics B 92, 13-18 (2008)

22. PMT Lock-in amplifier AOM Spatial light modulator grating  -metal (3 layers) chopper Solenoid coil grating Cs cell (Wall temperature 1000.001 0 C) C) 1/4 852 nm Pump laser Synthesizer Function Generator Loran-C Comb laser PZT CTSDL Control f n Control f rep Spectrum analyzer (FFT) Repetition rate Monitor f n, f rep PD Submit to PRL

23. experimental results 1500 Pascal N 2 +1500 Pascal He, mixed buffer gas

24. H=H 0 +H EM Dressed atom + H de radiative collision  Not a stable mixed state Brief introduction on Coherent Population Trapping (CPT) Ground state Not dipole allowed transition Clock frequency

25. PMT Lock-in amplifier AOM Spatial light modulator grating  -metal (3 layers) chopper Solenoid coil grating Cs cell (Wall temperature 1000.001 0 C) C) 1/4 852 nm Pump laser Synthesizer Function Generator Loran-C Comb laser PZT CTSDL Control f n Control f rep Spectrum analyzer (FFT) Repetition rate Monitor f n, f rep PD

26. Problems of CPT clocks 1.light shift and laser power broadening problem 2.need narrow linewidth as a frequency discriminator 3.buffer gas caused pressure shift H0=H0= 0 00 0 00 H EM = 0 0 0 00 H de = 0 0 0 0 0 0 0 CW CPT 86 kHz without buffer gas CW CPT with buffer gas 150 Hz

27. 050010001500200025003000 0 200 400 600 800 CW-light shift comb-light shft laser power (  W) light shift (Hz) Power insensitive character of comb-CPT (1)

28. Viewpoint in time domain Laser pulse Atom / molecule Dressed Atom/molecule Mixed state Time 1 ps 10 ns 1 ps 10 ns 1 ps 10 ns dressed wavefunction relaxes at quantum beat (clock frequency)

29. Theoretical simulation CW-CPT (140  W) 500 Hz -1.51.51-0.500.5 Normalized upper-level population Detuning from clock frequency (kHz) Comb-CPT (140  W) 40 Hz -0.4-0.200.20.4 Normalized upper-level population Detuning from clock frequency (kHz) Due to quantum interference effect

30. Comb laser CW laser

31. CW-CPT Power broadening (with buffer gas) CW-CPT Light shift (with buffer gas) - 80 - 60 - 40 - 20 0 20 406080 0.95 0.96 0.97 0.98 0.99 1.00 1.01 Fluorescence (Arb. unit) Detuning from clock frequency (mHz) 5.6 Hz Comb-CPT (with buffer gas) 2-order of magnitude narrower linewidth 2-order of magnitude improved light shift insensitive to pressure shift 45 Hz shift 950 Hz linewidth 0.8 Hz shift

32. Peak power: 1400 mW/cm 2 Kinetic energy of Ne collision cell~0.1 eV 852 nm, 1.46 eV 1 ps 100 mW/cm 2 (peak power) Ne Effective collision time: 0.3 ms CPT signal quenched One-photon saturation power (1 mW/cm 2 ) 6D 3/2 8S 1/2 0.2 eV 852 nm

33. Apply Physics B 92, 13-18 (2008) Pump laser PZT 1 Ti:S crystal PZT 2 Output coupler Translational stage prism 1 prism 2 A novel way on orthogonally controlling carrier-envelop phase