Frontiers in Laser Spectroscopy

ITALIAN PHYSICAL SOCIETY PROCEEDINGS OF THE INTERNATIONAL SCHOOL OF PHYSICS «ENRICO FERMI» COURSE GXX edited by T.W. HÄNSCH and M. INGUSCIO Directors of the Course VARENNA ON LAKE COMO VILLA MONASTERO 23 June - 3 July 1992 Frontiers in Laser Spectroscopy 1994 NORTH-HOLLAND AMSTERDAM - OXFORD - NEW YORK - TOKYO

INDICE T. W. HÄNSCH and M. INGUSCIO - Preface pag. xv Gruppo fotografico dei partecipanti al Corso fuori testo A. L. SCHAWLOW - Perspectives on laser spectroscopy. 1. Doppler broadening» 1 2. Simplifying spectra by laser labeling» 4 3. Observing small numbers of atoms» 6 4. Laser cooling» 6 5. Coherent-state superpositions» 8 6. Semiconductor lasers» 9 7. Measurement of optical frequencies» 11 8. Searching for weak lines» 12 LASER SPECTROSCOPY FIR -» UV W. DEMTRÖDEE, V. BEUTEL, H.-A ECKEL, H.-G. KRÄMER and E. MEHDIZADEH - Experimental techniques for high-resolution laser spectroscopy of small molecules and Clusters. 1. Introduction» 19 2. Sensitive detection techniques» 20 3. Sub-Doppler spectroscopy of Na 3» 23 4. Isotope-selective spectroscopy of silver dimers» 26 5. Lifetime measurements of selectively excited molecular levels» 31 v

M. INGUSCIO - High-resolution and high-sensitivity spectroscopy using semiconductor diode lasers. 1. Introduction 2. Overview on diode laser characteristics and Operation 3. Line narrowing and tuning with grating feedback 4. High-resolution spectroscopy of atoms 5. High-sensitivity spectroscopy of forbidden molecular transitions 6. Conclusions T. OKA - Application of laser spectroscopy to fundamental molecular species: H 3 + and solid H 2. 1. Introduction l'l. Natural constants and Orders of magnitude 1'2. Symmetry 2. Hj" in laboratory plasmas 2*1. Hydrogenic ions 2"2. TheH + 3 ion 2'3. Plasma spectroscopy 2'4. Observed spectrum 2'4.1. The v 2 fundamental band 2'4.2. Hot, overtone and forbidden bands 3. H + 3 spectroscopy in space 3'1. Astronomy and spectroscopy 3'2. H + 3 in interstellar space 3'3. H^ in Jupiter 3'4. H^ in other objects 4. Spectroscopy of solid hydrogen 4*1. Beginning 4'2. Background 4'3. Many-body absorption and high-aj spectrum 4'4. Fine structure due to intermolecular interaction 4'5. Stimulated Raman spectrum K. M. EVENSON - A history of laser frequency measurements (1967-1983): the final measurement of the speed of light and the redefinition of the meter. 1. Introduction 2. Measurement of laser frequencies 3. Project beginnings 4. World record frequency measurements 5. The speed of light 6. The fundamental constants 7. Frequency and wavelength Standards 8. The measurements of iodine 9. Iodine at the red He-Ne frequency 10. The final measurement of the speed of light 11. The new definition of the meter

INDICE VII 12. The rydberg pag. 99 13. The ]\HM and the synthesisoffar-infrared radiation» 100 14. The future» 101 B. P. STOICHEFF - Laser spectroscopy in the far-ultraviolet region. 1. Introduction» 105 2. Resume of theory» 106 3. Sources for generating tunable, coherent radiation» 108 31. VUV source developed at Toronto» 108 3'2. Sources of high brightness and monochromaticity» 113 4. Spectroscopic studies in the far ultraviolet» 114 4'1. Spectra of rare-gas excimers» 115 4'2. Radiative lifetimes of rovibronic levels in the A 1!^ = 0) state of CO» 119 4'3. Dependenceof Ar 2 radiative lifetimes on internuclear distance» 122 4'4. Dissociation energy of molecular hydrogen» 124 4'5. Second-harmonic generation (SHG) at 121.6 nm in atomic hydrogen» 128 4'6. SHG of Lyman-a radiation with reduced absorption» 131 SPECTROSCOPY AND SURFACE EFFECTS Y. R. SHEN - Surface spectroscopy by nonlinear optics. 1. Introduction» 139 2. Theory» 141 3. Experimental considerations» 147 4. Applications» 148 41. Buried interfaces» 150 4'2. Conformational changes of adsorbed molecules» 151 4'3. Polar orientations of molecules at interfaces» 153 4'4. Pure-liquid surfaces» 154 4'5. Hydrogen on Silicon and two-phonon bound states» 156 4'6. Hydrogen on diamond» 158 47. Dynamics of surface vibrations» 159 L. Moi - Gas manipulation by light. Introduction» 167 1. Resonance radiation pressure in a gas» 168 2. Light-induced drift» 173 21. Light-induced vapour jets» 174 2'2. White-light-induced drift» 177 2'3. LID-induced isotope Separation» 182 2'4. Light-induced atom desorption» 185 3. Conclusions» 187

VIII INDICE ULTRAHIGH RESOLUTION V. P. CHEBOTAYEV - High-resolution laser spectroscopy. 1. New possibilities of superhigh-resolution spectroscopy pag. 191 l'l. Narrowingofmultiphotonabsorptionresonances» 191 1'2. Application of the optical methods to microwave spectroscopy» 194 1'3. Method of separated optical fields and atomic interferometry» 196 1'4. Time Fourier high-resolution spectroscopy» 202 2. Second-order Doppler-free spectroscopy» 205 3. Laser stabilitron» 211 J. L. HALL - Frequency-stabilized lasers a driving force for new spectroscopies. 1. Introduction and overview» 217 2. The gas laser epoch» 218 2*1. Lamb-dip stabilization» 218 2'2. Intracavity saturated absorption atoms and molecules» 219 2'3. Saturated-absorption wavelength/frequency Standards redefinition of c» 222 2'4. Optical selection of the slowest atoms» 223 3. The tunable laser arrives» 225 3"1. Frequency stabilization is a severe problem for tunable lasers» 225 3'2. Cavity stabilization of tunable lasers» 225 3'3. Precision of locking to a cavity resonance» 227 4. Stability of the cavity resonance itself '..» 228 41. Estimating environmental requirements» 228 4'2. Active Vibration isolation» 229 4'3. Long-term cavity length/frequency stability» 230 5. Tuning the laser relative to a fixed cavity» 231 5T. Using an acousto-optic modulator for tuning» 231 5'2. Example 1: Line-narrowing and scanning a Ti:sapphire laser» 232 5'3. Example 2: Phase-locking laser diodes» 233 5'4. Moving to higher/wider frequency scans» 233 5'4.1. R.f. harmonic mixing in photodetector» 233 5'4.2. Broad-band modulation: modulator-in-a-cavity approach..» 234 6. Applications of stable lasers» 234 7. Conclusions» 236 FUNDAMENTAL EXPERIMENTS C. E. WIEMAN, S. GILBERT, CH. NOECKER, P. MASTERSON, C. TANNER, CH. WOOD, DONGHYUN CHO and M. STEPHENS - Measurement of parity nonconservation in atoms. 1. Introduction» 243 2. PNC neutral currents in atoms» 245 3. Experimental approaches» 248

INDICE IX 4. Design concepts of Colorado experiments pag. 252 5. Details of apparatus» 255 5*1. Signal and noise analysis» 255 5'2. Atomic beam» 257 5'3. Laser power build-up» 258 5'4. Detection» 260 5'5. Technical noise» 262 5*6. Servo Systems» 264 5'7. Field reversal and signal processing» 269 6. Systematic errors» 270 7. Implications» 275 8. Future improvements» 279 81. Near term» 279 8'2. Long term» 283 L. JULIEN, F. NEZ, M. D. PLIMMEE, S. BOURZEIX, R. FELDER and F. BIRABEN - High-resolution spectroscopy of the hydrogen atom; measurement of the Rydberg constant. 1. The Rydberg constant» 287 2. Spectroscopic measurements in atomic hydrogen» 288 3. The Paris experiment» 290 4. Study of the Signals» 291 5. Wavelength measurement» 292 6. Frequency measurement» 293 7. Result and perspectives» 294 T. W. HÄNSCH - Laser spectroscopy of atomic hydrogen. 1. Introduction» 297 2. Doppler-free two-photon spectroscopy of the 1S-2S transition» 299 3. Precision. measurement of the ISLamb shift» 303 4. Hydrogen-deuterium isotope shift of the 1S-2S frequency» 307 5. Absolute frequency of hydrogen 1S-2S and a new Rydberg constant» 308 6. Outlook» 312 S. CHU - Precision atom interferometry and an improved measurement of the 1 s S r 2 3 Si transition in positronium. 1. Stimulated Raman transitions and atom interferometry» 317 l'l. Stimulated Raman transitions» 318 1"2. Velocity selection with Raman transitions» 319 1*3. Optical Ramsey fringes» 322 1'4. Atom interferometry» 323 1*5. Interferometer phase shifts» 325 1'6. Fringe visibility» 326 1"7. The atomic-fountain apparatus» 327 1"8. Mechanical vibrations» 329

X INDICE 1'9. Results pag. 330 l'lo. Limits to resolution and accuracy.» 331 l'll. Speculations» 332 2. An interferometer measurement of the photon recoil velocity» 333 21. The interferometricmethodofmeasuring the photon recoil» 333 2'2. Experimental apparatus» 335 2'3. Experimental data» 337 2'4. Systematic effects» 338 2'5. Future work» 339 3. Positronium spectroscopy with a c.w. dye laser» 340 31. Status of theory» 341 3'2. Earlier optical spectroscopy of positronium» 343 3'3. Experimental apparatus» 344 3'4. Experimental results and analysis» 347 3'5. Future improvements» 351 ION TRAPS J. C. BERGQUIST, W. M. ITANO and D. J. WINELAND - Laser stabilization to a Single ion I. Spectrally narrow optical oscillators» 359 II. Frequency references» 359 F2. Reference cavity limitations» 360 F3. Experimental results: cavity comparisons» 366 II. Single-atom spectroscopy» 372 III. Single-ion results» 372 H. WALTHER - Single-atom experiments and the test of quantum physics. 1. Introduction» 377 2. Review of the one-atom maser» 377 3. The generation of nonclassical light in the one-atom maser» 381 4. Experimental results sub-poissonian statistics of atoms and photons» 382 5. A new probe of complementarity in quantum mechanics the one-atom maser and atomic interferometry» 387 6. Experiments with trapped ions the Paul trap» 391 7. Order vs. chaos: crystal vs. cloud» 393 8. The ion storagering» 398 9. Ordered structure in the storage ring» 400 10. Comparison with theory» 402 P. E. TOSCHEK - Single ions for metrology and quantum optics. 1. Introduction» 407 2. Line shapes of a Single ion» 409 3. Line shifts» 416

INDICE XI 4. Detectionof photon correlation as dynamic spectroscopy pag. 418 5. A trapped ion as a Schrödinger cat» 422 6. Observations on Single trapped ytterbium ion» 425 7. Summary» 427 G. WERTH - Precision hyperfine spectroscopy in ion traps. 1. Introduction» 431 2. Hyperfine structure of 207 Pb +» 434 3. Hyperfine structure of Eu + isotopes» 438 4. Conclusion» 440 COOLING J. DALIBARD and Y. CASTIN - Laser cooling from the semi-classical to the quantum regime. 1. Introduction» 445 2. Semi-classical description of laser cooling» 447 21. Validity of the semi-classical treatment» 447 2'2. The average radiative forces» 448 2'3. Fokker-Planck equation for the atomic phase space distribution» 449 2'4. Doppler cooling» 450 2'5. Sisyphus cooling» 452 3. The quantum regime of Sisyphus cooling» 456 3*1. Experimental and numerical results» 456 3'2. Principle of a quantum treatment» 458 3'3. Eigenstates of the Hamiltonian H» 459 3'4. Steady-state populations» 461 3"5. Conclusions for this approach» 463 4. A Monte Carlo wave function approach» 464 41. The MCWF procedure» 464 4'2. Equivalence with the master equation» 467 4'3. Connection with previous works» 469 4'4. Application to laser cooling» 470 4'4.1. The model» 470 4'4.2. Numerical results» 472 4'5. Conclusion for the MCWF approach» 473 ATOM INTERFEROMETERS M. SIGEL, C. S. ADAMS and J. MLYNEK - Atom optics. 1. Introduction» 479 11. Motivation for atom optical experiments» 479 1"2. Optical elements for atoms» 480 1*3. Outline» 482

XII INDICE 2. General principles ; pag. 483 21. Refraction and reflection of matter waves» 483 2'2. Diffraction of matter waves» 484 2'3. Interaction of atoms with light fields» 487 3. Beam Splitters for atoms» 490 31. Motivation» 490 3'2. Reflection from a crystal surface» 491 3'3. Diffraction from a transnlission grating» 491 3'4. Diffraction from an optical standing wave» 492 3"5. Bragg scattering» 495 3'6. Magneto-optical beam Splitter» 496 37. Optical Stern-Gerlach effect» 498 3'8. Beam Splitters based on single-photon recoil '.» 501 4. Interferometers for atoms» 501 41. Motivation» 501 4'2. Double-slit interferometer» 503 4'3. Three-grating interferometer» 504 4'4. Ramsey interferometer» 505 4'5. Interferometer using stimulated Raman transitions» 507 4'6. Longitudinal Stern-Gerlach interferometer» 509 5. Lenses for atoms» 509 51. Motivation» 509 5'2. Focussing using a Fresnel zone plate» 511 5'3. Focussing in static electric or magnetic fields» 512 5'4. Focussing in a co-propagating laser beam» 513 5'5. Cylindrical lens based on an optical standing wave» 514 5'6. Focussing using a curved mirror» 515 6. Mirrors for atoms» 516 61. Motivation» 516 6'2. Reflection from surfaces» 516 6'3. Reflection from an evanescent wave» 517 7. Conclusion» 519 QUANTUM OPTICS S. HAROCHE - Cavity quantum electrodynamics. 1. Introduction. Aim of this lecture» 527 2. Control of spontaneous emission in a cavity. Two complementary interpretations» 529 3. Energy shifts in cavity QED: van der Waals forces and other effects» 532 4. Resonant coupling of a two-level atom and a cavity: normal-mode Splitting effect» 536 5. «Rabi oscillation» and the micromaser» 539 6. Dispersive effects and manipulation of photons in cavity QED» 544 7. Extension to optical effects in microcavities» 549 8. Concluding remarks» 550

INDICE XIII E. GIACOBINO - Squeezed states of light. 1. Introduction pag. 555 2. Quantum fluctuations and squeezed states» 555 21. Coherent state and vacuum state» 557 2'2. Squeezed states» 558 2'3. Intensity measurements» 559 2'4. Model for a laser beam» 559 3. Quantum noise at the Output of a beamsplitter» 560 31. Homodyne measurements» 561 3'2. Effects of linear losseson squeezed light» 562 4. Generation of squeezed states» 563 41. Degenerate parametric generation» 563 41.1. Theory» 563 41.2. Experiments» 565 4'2. Bistability» 566 4'3. Nondegenerate parametric generation» 569 4'3.1, Theory» 569 4"3.2. Experiment» 571 5. Applications of squeezing to optical measurements» 573 51. Interferometric measurements» 573 5'2. Intensity measurements» 573 6. Conclusion» 573 CHAOS D. KLEPPNER - Quantum chaos and laser spectroscopy. 1. Introduction» 579 2. Energy levels and energy level statistics» 581 3. The diamagnetic hydrogen atom» 585 31. The classical diamagnetic hydrogen atom» 585 3'2. The quantum diamagnetic hydrogen atom» 587 4. High-resolution spectroscopy of the diamagnetic Rydberg atom» 587 5. Orderly structures» 589 6. Periodic-orbit spectroscopy» 592 7. Conclusion» 596