Contains research objectives and summary of research on eight research projects.National Science Foundation (Grant PHY75-15421-A01)U. S. Air Force - Office of Scientific Research (Grant AFOSR 76-2972)Joint Services Electronics Program (Contract DAAB07-76-C-1400)U. S. Air Force - Office of Scientific Research (Contract F44620-72-C-0057

Ahmad, Riad N.

Brunner, Timothy A.

Deutsch, Claude

Driver, Richard D.

Ducas, Theodore W.

Kleppner, Daniel

Lapatovich, Walter P.

Littman, Michael G.

McGrath, William R.

Moskowitz, Philip E.

Offner, Kurt W.

Pritchard, David E.

Smith, Neil

Spencer, William R.

Vaidanathan, A. Ganesh

Weinrib, Abel

Zimmerman, Myron L.

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V. ATOMIC RESONANCE AND SCATTERINGAcademic and Research StaffProf. Daniel KleppnerProf. David E. PritchardProf. Dieter ZimmermannRiad N. AhmadTimothy A. BrunnerWalter P. LapatovichDr. Claude DeutschDr. Richard D. DriverGraduate StudentsMichael G. LittmanPhilip E. MoskowitzJohn A. SerriDavid A. SmithDr. Theodore W. DucasDr. William D. PhillipsDr. Kermit R. WayWilliam R. SpencerA. Ganesh VaidanathanMyron L. Zimmerman1. SEEDED MOLECULAR BEAM SOURCENational Science Foundation (Grant PHY75-15421-A01)Riad N. Ahmad, Walter P. Lapatovich, William R. McGrath, David E. PritchardWe have built and started to operate a molecular beam source designed to producemolecules in a low-temperature nonequilibrium environment for laser spectroscopyand molecular scattering experiments. The source is a rare-gas beam at very highpressure (>100 atm) which can be " seeded " with various minor constituents such as Na.Fig. V-l. Sample spectrum with 7 K rotational temperature.PR No. 119(V. ATOMIC RESONANCE AND SCATTERING)We have succeeded in producing NaNe molecules which are bound by only ~0. 002 eV,and have observed several rotational bands of this molecule. We also have observedNa 2 bands with very low rotational temperatures. A sample spectrum with 7 K rota-tional temperature is shown in Fig. V-l.2. ROTATIONAL ENERGY TRANSFER MEASUREMENTS WITHVELOCITY-SELECTED MOLECULESU. S. Air Force - Office of Scientific Research (Grant AFOSR 76-2972)David E. Pritchard, Richard D. Driver, Timothy A. Brunner, Neil SmithWe are studying the processes of rotational energy transfer for Na 2 molecules incollision with Ar atoms. By using the VSDS technique proposed by Phillips andPritchard,1 we shall measure the velocity-dependent cross sections of the collision pro-cess, Na2 (v, J) + Ar = NaZ(v, J±AJ) + Ar + AE, where (v, J) are the vibrational-rotationalquantum numbers of the molecular initial state.In July 1976 we received the first commercially available Coherent RadiationModel 599 cw dye laser. This has a single-mode output bandwidth of less than 10 MHzand is continuously tunable over a 30-GHz range. The Na 2 molecules are produced ina stainless-steel oven. Approximately 10% of the sodium vapor is in molecular form.The laser and oven are both working satisfactorily. We have made a detailed study ofthe Na 2 rotational-vibrational spectrum in the 610 mm wavelength region by observingthe total fluorescent light signals as we scan the input laser beam into the oven. Wehave selected a number of lines in the total fluorescence spectrum and observed thewavelength dependence of their fluorescence with a scanning monochromator. Using sucha spectrum and available published molecular constants for Na 2 , we have been able todesignate (v,J) quantum numbers for the upper and lower energy levels of the transi-tions. We have observed collisionally induced, pressure-dependent satellites in thewavelength-dependent fluorescence spectrum corresponding to the rotational energytransfer processes of interest, and shall continue to study these processes.Data acquisition is carried out with the aid of a PDP-11 computer. The detectionsystem is buffered into the computer via a CAMAC molecular system. Computer pro-grams have been written to collect and reduce the experimental data. The preliminarywork has shown that the system is working satisfactorily.References1i. W. D. Phillips and D. E. Pritchard, "Velocity Selection by Doppler Shift: A Gen-eral Method for Studying Excited-State Collisions," Phys. Rev. Letters 33, 1254-1257 (1974).PR No. 119(V. ATOMIC RESONANCE AND SCATTERING)3. OPTICAL FREQUENCY STANDARDSJoint Services Electronics Program (Contract DAAB07-76-C-1400)Walter P. Lapatovich, Philip E. Moskowitz, Kurt W. Offner, Abel Weinrib,David E. PritchardThe Mark I optical-frequency reference system was used to make the frequencymarks shown in Fig. V-2. A new Mark II optical-frequency reference system has beendesigned and a prototype has been tested. It will provide continuous fast read-out of thefrequency so that it can be used to servo-control the laser frequency. The device willalso be interfaced to a computer.LASER SERVOSTABILIZERTO SERVO MIRRORMOUNT144FRESNEL RHOMBOPTIC AXISOPTICS ANDPHOTODIODEANALYZINGPOLARIZERQUARTZCRYSTALd c MOTOR ELECTRONICSTO COMPUTERFig. V-2. Optical-frequency reference system.The heart of the new system is an optical interferometer that rotates the linearpolarization of the incident laser light by an amount proportional to its frequency; inthe device under construction the rotation is 10 for each ~600 MHz increase in fre-quency. This interferometer has a linear polarizer, a birefringent element (a quartzcrystal is used in the prototype) whose optic axis is shifted 450 with respect to the polar-izer, a quarter-wave plate set with its optic axis parallel to the polarizer, and an auto-mated sensor for finding the angle of polarization. This device functions as follows: Twoorthogonally linearly polarized light beams with a relative phase delay proportional tothe frequency are produced by the birefringent element. These beams are convertedinto oppositely rotating circularly polarized light beams by the quarter-wave plate,PR No. 119(V. ATOMIC RESONANCE AND SCATTERING)and they interfere to give a linearly polarized beam whose angle increases linearly withthe phase delay. This angle is then converted into electrical information suitable forcontrolling or indicating the frequency.4. SUBMILLIMETER PHOTON COUNTINGJoint Services Electronics Program (Contract DAAB07-76-C-1400)Daniel Kleppner, Myron L. Zimmerman, Michael G. LittmanWe have started to develop a new technique for detecting millimeter and submilli-meter radiation, using a gas of highly excited atoms as the working medium. Resonancetransitions are induced between suitably chosen levels, and detected by field ionizationof the final state. Under certain conditions, the system gives promise of allowing effi-cient and quiet photon counting in the millimeter and submillimeter ranges. Continuoustuning is possible by using the first-order Stark effect.Experimental work includes construction of a CO 2 10 p.m laser, and of a CH3F496 pim laser for use as spectral sources. Resonance transitions have been detected at10 pm. Calculations of transition moments for Stark-shifted levels are in progress.5. STUDIES IN OPTICAL PHYSICS AND EXCITED-STATEINTERACTIONSJoint Services Electronics Program (Contract DAAB07-76-C-1400)Theodore W. Ducas, William R. Spencer, A. Ganesh Vaidanathan,Daniel KleppnerNew methods for exciting atoms to high Rydberg states are needed in a variety ofexperiments and for practical applications. We have undertaken the cw excitation ofRydberg states in an atomic beam, using two-photon transitions and single-photon tran-sitions with frequency-doubled light. The frequency-doubling system has been broughtinto operation, and a new atomic beam apparatus has been constructed. This apparatusis designed to allow motion of Rydberg atoms from an excitation region to interactionand detection regions. The system should soon be fully operable.6. THEORETICAL STUDY OF ATOMIC RYDBERG STATESJoint Services Electronics Program (Contract DAAB07-76-C-1400)Claude DeutschIn order to lend theoretical support to the experimental study of the Rydberg statesof light elements and alkalies undertaken by Daniel Kleppner and his co-workers, wePR No. 119(V. ATOMIC RESONANCE AND SCATTERING)have reconsidered and generalized the polarization model determination of the highly1located hydrogenic levels. First, we considered neutral helium, and obtained non-adiabatic corrections to the R - 6 and R 7 polarization potential. The extension of thisresult to the alkalies by retaining the fine-structure term in the zero-order approxima-tion is straightforward. We have also studied the behavior of hydrogen Rydberg statesin the presence of a magnetic field so strong that perturbation theory is no longer valid.This problem has been approached by factorizing the nonrelativistic wave function intoa product of a two-dimensional harmonic oscillator and a one-dimensional coulombhydrogen atom. Extensions of this basic scheme to allow for the inclusion of magneticintensities of any intermediate value are now being investigated.References1. C. Deutsch, "Rydberg States of HeI Using the Polarization Model," Phys. Rev. A 13,2311-2313 (1976).7. FIELD IONIZATIONU. S. Air Force - Office of Scientific Research (Contract F44620-72-C-0057)Michael G. Littman, Daniel KleppnerThe problem of finding out how an atom ionizes in an applied electric field hasreceived much attention for several years, and now the theory for hydrogen is welldeveloped. We have carried out the first precise study of field ionization by measuringionization rates for highly excited states of sodium. We have obtained excellent agree-ment with hydrogenic theory for some states, but the ionization rates are in seriousdisagreement for most states. The source of the disagreement was found to be theeffects of level mixing that had been neglected previously. The problem is of theoret-ical interest and of considerable practical importance because field ionization is widelyused for detecting highly excited atoms.1Further details of this work have been published recently.References1. M. G. Littman, M. L. Zimmerman, and D. Kleppner, "Tunneling Rates for ExcitedStates of Sodium in a Static Electric Field," Phys. Rev. Letters 37, 486-489 (1976).PR No. 119(V. ATOMIC RESONANCE AND SCATTERING)8. ATOMS IN VERY HIGH MAGNETIC FIELDSNational Science Foundation (Grant PHY75-15421-A01)Myron L. Zimmerman, Daniel KleppnerThe effect of magnetic fields on atoms is usually so weak that it can be treated as afirst-order perturbation. At high fields diamagnetic terms become important. The22 2 2 2interaction is of the form 3 Cd = e B (x +y )/8mc . The diamagnetic energy WB scalesas (r ) B Z . For an atom in a Rydberg state (a highly excited state), ( r ) n4, wheren is the principal quantum number. The electrostatic energy WE scales as 1/n , so6 B2Zthat the ratio of electron and magnetic interactions, WB/WE, scales as n B . For n 30,it is possible to achieve the condition WB > WE with a field of 100 kG. In such a situa-tion the atom loses many of its familiar properties and becomes essentially a new quan-tum system.We have undertaken a study of Rydberg atoms in high magnetic fields, using pre-1viously developed techniques for exciting and detecting atoms. An atomic beam appara-tus has been constructed for use in conjunction with a 100 kG superconducting solenoid.The apparatus is essentially complete and we plan to start high-field measurementssoon.References1. T. W. Ducas, M. G. Littman, R. R. Freeman, and D. Kleppner, "Stark Ionizationof High-Lying States of Sodium," Phys. Rev. Letters 35, 366-369 (1975).PR No. 119

Atomic Resonance and Scattering

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Atomic Resonance and Scattering

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