Contains reports on nine research projects.U.S. Energy Research and Development Administration (Contract EG-77-S-02-4370)U. S. Air Force - Office of Scientific Research (Contract F44620-72-C-0057)Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Science Foundation (Grant PHY75-15421-AO1)National Science Foundation (Grant PHY77-09155)National Science Foundation (Grant CHE76-81750)U. S. Air Force - Office of Scientific Research (Grant AFOSR-76-2972A

Ahmad, Riad N.

Al-Agil, Ibrahim

Brunner, Timothy A.

Castro Neto, Jarbas C.

Driver, Richard D.

Ducas, Theodore W.

Ely, Douglas J.

Kash, Michael M.

Kinsey, James L.

Kleppner, Daniel

Lapatovich, Walter P.

Littman, Michael G.

McGrath, William P.

Metcalf, Harold J.

Moskowitz, Philip E.

Phillips, William D.

Pritchard, David E.

Serri, John A.

Smith, Neil

Spencer, William P.

Vaidyanathan, A. Ganesh

Wainger, Mark D.

Walkup, Robert E.

Way, Kermit R.

Zimmerman, Myron L.

DSpace@MIT

V. ATOMIC RESONANCE AND SCATTERINGProf. Daniel KleppnerProf. David E. PritchardDr. Stuart S. B. Crampton:*Dr. Richard D. DriverRiad N. AhmadIbrahim Al-AgilTimothy A. BrunnerJarbas C. Castro NetoNeal S. HermanowiczAcademic and Research StaffDr. Theodore W. DucastDr. MichaelG. LittmanDr. Harold J. MetcalftGraduate StudentsMichaelM. KashWalter P. LapatovichPhilip E. MoskowitzJohn A. SerriDr. William D. PhillipsDr. Kermit R. WayDr. Haider R. ZaidiWilliam M. HamiltonNeil SmithWilliam P. SpencerA. Ganesh VaidyanathanRobert E. WalkupMyron L. Zimmerman1. FIELD IONIZATION AND PHOTOIONIZATIONU.S. Energy Research and Development Administration (Contract EG-77-S-02-4370)Daniel Kleppner, Michael G. Littman, Michael M. Kash, Harold J. MetcalfWe have constructed a new tunable dye laser system for the study of field ionizationin highly excited atoms. Pump power is provided by a Quanta Ray Nd:YAG laser withsecond, third, and fourth harmonic generators. A new type of dye laser has beendevised which has important advantages of simplicity and economy. Work has begunon a study of field ionization of lithium. The atom is prepared in a Rydberg stateby a three-step excitation process, using two fixed-frequency and one tunable dyelasers.2. HIGHLY EXCITED ATOMSU. S. Air Force - Office of Scientific Research (Contract F44620-72-C-0057)Daniel Kleppner, Theodore W. Ducas, Michael G. Littman, Myron L. ZimmermanWe have carried out a study of the Stark structure of barium. The aim of this workwas to study a two-electron atom in a region where a valence state (a low-lying stateof the excited core) interacts with a Rydberg progression. The interactions of thevalence state with the Rydberg manifolds were clearly displayed. The system was ana-lyzed by combining a simple configuration-interaction picture with a calculational methodVisiting Faculty Fellow from Williams College.TAssistant Professor at Wellesley College.T Visiting Associate Professor from State University of New York at Stony Brook.PR No. 120(V. ATOMIC RESONANCE AND SCATTERING)previously developed for analyzing one-electron Rydberg Stark structure. A paper onthe work1 will appear in J. Phys. B.References1. M. L. Zimmerman, T. W. Ducas, M. G. Littman, and D. Kleppner, "Stark Struc-ture of Barium Rydberg States."3. SUBMILLIMETER PHOTON COUNTINGJoint Services Electronics Program (Contract DAABO7- 76-C- 1400)Daniel Kleppner, Theodore W. Ducas, William P. Spencer,A. Ganesh VaidyanathanWe have constructed a FIR laser and have observed resonance transitions in Ryd-berg atoms at 118 m and 496 min. A number of transitions at CO 2 wavelengths near10 tm have also been observed. Work has begun on a study of noise sources and theresonance line shape of the proposed detection. A millimeter wave phase-locked kly-stron system is under construction; it will be used for the study of millimeter wave res-onance transitions.4. STUDIES IN OPTICAL PHYSICSJoint Services Electronics Program (Contract DAAB07-76-C-1400)Daniel Kleppner, Michael G. Littman, William P. Spencer,A. Ganesh VaidyanathanWe have developed methods for producing highly excited states of a variety of atoms,including all the alkalis and several of the alkaline earths. Both cw and pulsed lasertechniques have been used. A new apparatus has been constructed for high-resolutionspectroscopic studies, and techniques have been developed for introducing infrared andmillimeter-wave radiation to the atomic beam interaction region.5. STUDIES IN ATOMIC PHYSICSNational Science Foundation (Grant PHY75- 15421 -AO 1)Daniel Kleppner, Myron L. Zimmerman, Jarbas C. Castro NetoWe have obtained initial results on a study of a highly excited one-electron atom ina high magnetic field. The problem is of interest because the system is fundamentallyPR No. 120(V. ATOMIC RESONANCE AND SCATTERING)simple, yet no comprehensive theory exists. An atomic beam of sodium was excited bytunable dye lasers in the center of a superconducting solenoid, and the structure of levelswith principal quantum numbers in the vicinity of n = 25 was studied in magnetic fieldsup to 65 kG. The diamagnetic interaction, normally an extremely small perturbation,was large enough to mix several terms. We have analyzed the data using a perturbativeapproach based on all terms in the range 22 < n < 31. Quantitative agreement is good.The work is being extended to larger values of n, where the structure starts to resembleLandau levels.6. SPECTROSCOPY OF VAN DER WAALS MOLECULESNational Science Foundation (Grant PHY77-09155)Riad N. Ahmad, Walter P. Lapatovich, William P. McGrath,Philip E. Moskowitz, David E. PritchardThe sodium neon (NaNe) data obtained from our seeded molecular beams machinelhas been analyzed in some detail. The ground state well depth of this weakly bound mol--3ecule is found to be DOX = 10 eV, and the equilibrium separation of Na and Ne atoms-8 O-2is re = 5. 3 10 . 8 cm; for the first excited state we find DA = 1. 74 x 10 - Z eV and R --82. 7 x 10 - . This means that NaNe is, by almost an order of magnitude, the weakestdiatomic molecule to be studied in an isolated condition. Experimental determinationof these interatomic potentials shows several theoretical calculations 2 ' 3 to be in errorand provides a method of determining the applicability of certain techniques used to ana-lyze earlier rare gas-alkali scattering data.4 Our apparatus is now undergoing substan-tial modification so that we may conclude our study of the NaNe complex and continueon to investigate other systems.References1. RLE Progress Report No. 119, January 1977, p. 13.2. W. E. Baylis, J. Chem. Phys. 66, 3778 (1977).3. J. Pascale and J. Vanderplanque, J. Chem. Phys. 60, 2278 (1974).4. G. M. Carter, D. E. Pritchard, M. Kaplan, and T. W. Ducas, Phys. Rev. Let-ters 35, 1144 (1975).PR No. 120(V. ATOMIC RESONANCE AND SCATTERING)7. COLLISIONAL BROADENING OF THE Na D LINESNational Science Foundation (Grant PHY77-09155)Douglas J. Ely, William D. Phillips, Robert Walkup, David E. PritchardCollisional broadening of the Na D lines has long been a subject of intensive theoret-ical and experimental investigation, both because of interest in the fundamental processand for application to the study of such lines in stellar atmospheres. We have begunexperiments which, in contrast to most previous work on the subjects, employ techniquesto study sub-Doppler collision broadening. One is saturated absorption spectroscopy,which can be used selectively to observe only those atoms having a specific velocity alonga given axis. Thus the velocity dependence of line broadening processes can be studiedwith increased resolution over current methods which use temperature dependence toinfer velocity dependence. Four-wave mixing, a technique in which three laser beamscreate a polarization in Na vapor which radiates a fourth coherent beam, can also beused to study line broadening and has the advantage of being able to select more thanone component of the Na velocity. Finally, using photon counting techniques to observelaser- induced fluorescence in Na vapor, one can detect the small Lorentzian absorptionwings of the collisionally broadened Na line at frequencies well beyond the Dopplerwidth. These various techniques all yield information about the collisional linewidthfor widths small compared with the Doppler width. The last technique can also easilybe used for linewidths greater than the Doppler width, so we can make contact betweenthe two regimes of collisional broadening. Work is in the preliminary stages. We haveobserved saturated absorption and fluorescent signals, as well as four-wave mixingsignals.8. DIFFERENTIAL CROSS-SECTION MEASUREMENTS USINGDOPPLER SELECTIVE LASER FLUORESCENCE ANALYSISNational Science Foundation (Grant CHE76- 81750)David E. Pritchard, Douglas J. Ely, William D. Phillips, John A. Serri,Kermit R. Way, James L. Kinsey[James L. Kinsey is Professor in the Department of Chemistry, M. I. T.]By placing a cw narrow-band dye laser along the relative velocity axis of two atomicbeams in a crossed-beam experiment, we are able to detect the scattered velocity dis-tribution of one of the beams by Doppler-tuning the atoms into resonance and detectingtheir subsequent fluorescence. Atoms are excited into resonance when the projectionof their velocity along the direction of the laser beam, vp = v cos 0cm, is equal toPR No. 120(V. ATOMIC RESONANCE AND SCATTERING)c(v-vo)/ o0 . The frequency vo represents the rest frame resonance frequency and vselects a certain velocity component. By recording the fluorescence signal as a functionof v, we directly obtain the center of mass differential cross section versus cos 0cmTransformation from laboratory angles to center-of-mass angles is not required in theanalysis. The collision we studied wasNa (3P 1/ 2 ) + Ar - Na (3P 3 / 2 ) + Ar - .002 eV.The first excited state of sodium was produced by a velocity selective laser beam,Doppler-tuned to excite the 3S 1/2 to 3P1/2 transition. Another laser, tuned to the 3P3/ 2to 4D transition, detected Na (3P 1/ 2 ) that underwent the fine structure changing colli-sion. The detection signal resulted from the 4P - 3S transition after the atom decayedfrom the 4D - 4P state. Our measured cross sections yielded oscillatory structurewhich seems to be in approximate agreement with recent theoretical calculations. Con-struction of a new beams machine is now under way to use this technique (coined VADS,Velocity Analysis using the Doppler Shift) on molecular systems. We plan to measurethe angular differential cross section for state-to-state, vibrational, and rotationalchanging collisions of Na 2 upon collision with a rare gas atom. Supersonic oven sourceswill be utilized to provide a cold Na2 beam of high density, and to provide a narrowvelocity distribution for both beams.9. STUDIES OF ROTATIONAL ENERGY TRANSFERU. S. Air Force - Office of Scientific Research (Grant AFOSR-76-2972A)Ibrahim Al-Agil, Timothy Brunner, Richard D. Driver, David E. Pritchard,Neil Smith, Mark D. WaingerWe have studied the rotational energy transfer processNa 2 (vj) + Xe = Na(v, j+ A j) + Xe - AEwhere a Na 2 molecule, in the excited A electronic state and with vibrational and rota-tional quantum numbers v and j, respectively, collides with a xenon atom and changesits rotational quantum number to j + Aj with a corresponding loss AE in translationalenergy. We have used the velocity selection by Doppler shift techniquel to obtain thevelocity dependence of the rotational changing rate constants. The experimental rateconstants obtained using the VSDS technique have some thermal averaging present fromthe velocity components which are unspecified by the exciting laser. We have developeda Fourier transform deconvolution technique which permits us to obtain the dependenceof the rate constants on relative velocity from the experimental data. An example ofthis experimental data, together with the deconvoluted rate constant, is shown inPR No. 120(V. ATOMIC RESONANCE AND SCATTERING)Fig. V-I for the v = 18, j = 38 state for a collision with Aj = -2. A paper describingthis work is in preparation.We have studied the dependence of the cross sections for a given initial j on Aj andnoted how our data change with different initial j within a given vibrational state. ThesexlO-10o5.0Fig. V-1.E 4 .o Plots of the experimental and deconvoluted rateconstants with collision velocity for jinitial= 38o and Aj = -2.2 --- Deconvoluted data vs v .,' Experimental data vs vrel.150 xIl4VELOCITY (cm/s)I.OO~F-1.0U) FZ-0 ZtI "0.0UjZ0(n0UZ100ENERGY DEFECT I AE, IN cm-,Plot of the cross section/density of final states against theenergy defect of the collision. The density of the final statesis the product of the rotational final state density (Zj'+l) andthe momentum state density a = [E-E ,/E-E ]1/2A Experimental data Aj < 0 collisions.+ Experimental data Aj > 0 collisions.Parametrized fits of the form +In [r-jj/(Zj'+l)a] =-a In AEjj - bAEjj, - c.For Aj < 0 the parameters are a = -0. 789, b = -0.00219,c = 1.142. For Aj > 0 the parameters are a = -0. 642, b =-0.0095, c = 0. 754.PR No. 120Fig. V-2.(V. ATOMIC RESONANCE AND SCATTERING)data are extremely valuable in the light of recent theories of rotational energy transferusing the information-theoretic-based prediction of surprisal theory. 2 We have provedconclusively that the linear surprisal model is not adequate to describe our experimentaldata, and we will shortly be in a position to differentiate between a number of the alter-native surprisal theories recently proposed (see Fig. V-2). Our experiment representsthe most definitive experimental study of atom-diatom energy transfer so far undertaken:selections of the initial and final vibrational-rotational levels of the diatomic have beenmade and we have studied the velocity dependence of the collision cross section.References1. W. D. Phillips and D. E. Pritchard, Phys. Rev. Letters 33, 1254 (1975).2. R. D. Levine, R. B. Bernstein, P. Kahana, I. Piscaccia, and E. T. Upchurch,J. Chem. Phys. 64, 1796 (1976).PR No. 120

Atomic Resonance and Scattering

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Atomic Resonance and Scattering

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