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In Search of the “Absolute” Optical Phase

In Search of the “Absolute” Optical Phase. Pete Roos (JILA, NIST, CU). JILA, NIST, CU (Boulder). U of T (Toronto). Xiaoqin (Elaine) Li Ryan Smith Jessica Pipis Steve Cundiff Rich Mirin. Tara Fortier David Jones. Ravi Bhat John Sipe. Important concepts and motivation.

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In Search of the “Absolute” Optical Phase

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  1. In Search of the “Absolute” Optical Phase Pete Roos (JILA, NIST, CU) JILA, NIST, CU (Boulder) U of T (Toronto) Xiaoqin (Elaine) Li Ryan Smith Jessica Pipis Steve Cundiff Rich Mirin Tara Fortier David Jones Ravi Bhat John Sipe

  2. Important concepts and motivation • How fast is ultrafast? • The “Absolute” optical phase. • Why do we care? Creation and control of ultrashort pulses • Modelocking. • “Absolute” phase evolution – time vs. frequency. • Detection methods. Quantum interference control (QIC) in semiconductors • Background. • Concepts and theory. • Experimental studies and stabilization using QIC. Outline

  3. 1 s 1 fs How Fast is Ultrafast? • Within an order of magnitude or two of 10 fs (1 fs = 10-15 s). • Scaling example:

  4. Optical carrier cycle (~ 3fs) Carrier-envelope (CE) phase Envelope Pulse Duration (~10 fs) Carrier “Absolute” Optical Phase • Ultrafast optics approaching interesting regime: • Pulse envelope provides “absolute” phase reference.

  5. Why do we care? 1. Can affect light-matter interactions. • Extreme nonlinear optics. • Photoionization and x-ray generation. • Photoelectron emission from metal surfaces. • Coherent control experiments. 2. Ultimate control of light. • Not only control of intensity envelope … field. • Optical waveform synthesis. • AWG at optical frequencies. 3. Precision measurements. • Optical frequency metrology. • Linear / nonlinear spectroscopy.

  6. Important concepts and motivation • How fast is ultrafast? • The “Absolute” optical phase. • Why do we care? Creation and control of ultrashort pulses • Modelocking. • “Absolute” phase evolution – time vs. frequency. • Detection methods. Quantum interference control (QIC) in semiconductors • Background. • Concepts and theory. • Experimental studies and stabilization using QIC. Outline

  7. External switch: Switch Gain Output beam Pulses Mirrors Internal switch: Switch Gain Pulses Mirrors Short Laser Pulses

  8. 30 modes all in phase 30 modes random phases Ultrashort Laser Pulses Modelocking: Intensity Frequency Intensity Time • Coherent interference effect. • Requires phase locked modes.

  9. CE Phase Instability • In laser cavity: vgroup≠ vphase • CE phase evolves from pulse to pulse outside cavity. Laser Cavity Free Space High Reflector Output Coupler

  10. Random Evolution • Uncontrolled CE phase evolution: • Limits meaningful physics and applications.

  11. No Evolution • Fixed CE phase: • Enables meaningful physics and applications.

  12. Df Df Df Df Df Controlled Evolution • Controlled CE phase evolution: • Also enables meaningful physics and applications.

  13. fce tp fce t fce fce F.T. I(n) frep=1/t fce fce Frequency Domain fce ~1/tp fce fce fce n 0 2n, fce x2 n, fce fce 2n, 2fce Time vs. Frequency Domain E(t) Time Domain t

  14. Df 2Df F.T. f0=frepDf/2p I(n) Frequency Domain n 0 2n+f0 x2 n+f0 2n+2f0 f0 Time vs. Frequency Domain E(t) Time Domain t

  15. n Second harmonic generation (n-to-2n) 2 Telle et al., Appl. Phys. B (1999); Jones et al., Science 288, 635 (2000); Apolonski et al., PRL 85, 740 (2000) 2n Photoionization of gases Durfee et al., PRL 83 2187 (1999); Paulus et al., Science 414, 182 (2002) vapor Photoelectron emission from metals metal Lemell et al., PRL 90, 076403 (2003); Apolonski et al., PRL 92, 073902 (2004) Rabi sideband interference semiconductor Vu et al., PRL 92, 217403 (2004); Mücke et al., Opt. Lett. 29 2160 (2004) 3, Rabi Some Detection Methods

  16. Important concepts and motivation • How fast is ultrafast? • The “Absolute” optical phase. • Why do we care? Creation and control of ultrashort pulses • Modelocking. • “Absolute” phase evolution – time vs. frequency. • Detection methods. Quantum interference control (QIC) in semiconductors • Background. • Concepts and theory. • Experimental studies and stabilization using QIC. Outline

  17. fb fn fd f2n fa fn fc Relative optical phase can coherently control: Semiconductor charge currents State population Haché et al, PRL 78, 306 (1997) Shapiro et al, J Chem Phys 84, 4103 (1986) Atomic photoionization Semiconductor spin currents Yin et al, PRL 69, 2353 (1992) Bhat et al, PRL 85, 5432 (2000) Molecular photodissociation Sheehy et al, PRL 74, 4799 (1995) Quantum Interference • Two distinct quantum mechanical pathways. • Connect same initial and final states. ~sin(2fn-f2n) ~sin[(fa+fb)-(fc+fd)]

  18. fce fce QIC in Semiconductors • Quantum interference between 1 and 2 photon absorption. • Asymmetry in momentum space  directional current. • Sensitive to relative phase betweenn and 2n. sin(2fn-f2n)  sin(2fce-fce) = sin(fce) • Photocurrent direction and magnitude sensitive to CE phase.

  19. Transition Amplitudes Charge { } Velocity One-photon Two-photon QIC in Semiconductors From Fermi’s Golden Rule: Atanasov et al., PRL 76, 1703 (1996); Hachéet al., PRL 78, 306 (1997)

  20. Transition Amplitudes Charge { } Quantum Interference Velocity One-photon absorption Two-photon absorption Atanasov et al., PRL 76, 1703 (1996); Hachéet al., PRL 78, 306 (1997) QIC in Semiconductors

  21. { } Quantum Interference One-photon absorption Two-photon absorption QIC in Semiconductors Even in k

  22. { } Quantum Interference One-photon absorption Two-photon absorption QIC in Semiconductors Even in k Odd in k

  23. { } Quantum Interference One-photon absorption Two-photon absorption QIC in Semiconductors Even in k Odd in k Odd in k

  24. Simplified Setup Stabilized Ti:sapphire modelocked laser ~15 fs, 93 MHz rep. rate, up to 400 mW avg. power Time delay adjust Fiber broadening Prism n Split mirror LT-GaAs 2n Lens Prism Sample Lock-in amplifier I/V RF spectrum analyzer

  25. Signal Amplitude Current ≈ 100 pA • Now have >500 pA.

  26. Incident Power • < J > ~ In (I2n)1/2 Roos et al., JOSA B (to be published)

  27. CE Phase Sensitivity • Verification that phase of QIC signal varies with shifts in carrier-envelope phase. Fortier et al., PRL 92, 147403 (2004)

  28. Detection Bandwidth • With transimpedance amplifier: 830 kHz. Roos et al., JOSA B (to be published)

  29. To phase noise analysis Simplified Stabilization Setup Ti:sapphire laser Prism High reflector Pump Output coupler Ti:sapphire crystal Prism Time delay adjust Fiber broadening n Split mirror 2n Lens Sample Mixer Stabilization electronics I/V ~ Synthesizer

  30. Stabilization via QIC • CE phase evolution stabilized. Roos et al., Opt. Lett. (to be published)

  31. Summary • “Absolute” (carrier-envelope) phase: phase difference between carrier peak and envelope peak. • Important for light-matter interactions, optical waveform synthesis, precision measurements. • Modelocked lasers enable access to “absolute” phase. • To detect: compare phase of spectral components in frequency domain through nonlinear process. • Quantum interferencecontrol (QIC) in semiconductors gives phase-sensitive photocurrent. • “Absolute” phasestabilization using QIC.

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