Contains reports on nine research projects.National Science Foundation (Grant PHY82-10369)Joint Services Electronics Program (Contract DAAG29-83-K-0003)U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)Litton Guidance and Control SystemNational Science Foundation (Grant PHY82-10369

Chou, Harry

Ezekiel, Shaoul

Hemmer, Philip H.

Jain, Sudhanshu H.

Kierstead, John

Kleinmann, Bertrand

Ontai, Guy P.

Prentiss, Mara G.

Shu, Roberto

Tench, Robert E.

Zarinetchi, Farhad

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Quantum Optics and Photonics20. Quantum Optics and PhotonicsAcademic and Research StaffProf. S. Ezekiel, Dr. B. Kleinmann, Dr. P.R. Hemmer, J. KiersteadGraduate StudentsH. Chou, D. DiFillipo, S.H. Jain, F. Long, R.E. Meyer, V. Natoli, C. O'Connor,G. Ontai, B.W. Peuse, D.R. Ponikvar, M.G. Prentiss, G.A. Sanders, S. Shu, R.E.Tench, E. Young, F. Zarinetchi20.1 Precision Studies of Doppler-Free LineshapesGenerated by Pump-Probe Interactions in a VaporNational Science Foundation (Grant PHY82-10369)Joint Services Electronics Program (Contract DAAG29-83-K-0003)Robert E. Tench, Shaoul EzekielThe interaction of monochromatic radiation with two and three level quantum systems is ofmuch interest because it involves basic physical processes which can be described by relativelysimple theoretical models. As part of our continuing investigations of basic atom-fieldinteraction, we have performed a precision experimental study of the interaction of twomonochromatic laser fields with a folded. Doppler-broadened three level system in 12 vapor.Studies were performed both for copropagating fields (forward scattering) andcounterpropagating fields (backward scattering); in both cases, the measured quantity was thegain induced at the frequency of a weak probe field in the presence of a pump field of arbitrarystrength.The experimental setup consisted of a CW argon ion laser operating at 5145 A (the pump), a CWdye laser operating near 5830 A (the probe), a single mode fiber and a cell containing 12 vapor.Fast frequency stabilization techniques were used to reduce the short-term linewidths of thelasers to a few kHi--z rms. Long-term frequency stability was achieved by locking the argon laser toa molecular reference and transferring the long-term stability of the argon laser to the dye laservia a transfer Fabry-Perot cavity. Precision laser tuning was then accomplished by using anacousto-o)ptic tfreIqlmency shifter which onperated at freqluencies between 100 and 200 MHz.C;ollinear pump and 'robe fields were generated by coupling both lasers into a single modelfiber,' and lineshLapes are recorded by holding the pump frequency fixed and scanning the probefrequency.Experimental studies of forward and backward scattered lineshapes were carried out in theRILE P.R. No. 127121Quantum Optics and Photonicsweak and strong pump field limits. The forward and backward lineshapes obtained with weakpump fields were found to be Lorentzians of different widths. the forward scattered line had awidth of 40 kHz. The experimental weak field lineshapes and linewidths were in excellentagreement with the predictions of a steady state theoretical model of the pump-probeinteraction.1 For intense pump fields, however, an apparent splitting was observed in thebackward scattered case which is not predicted by the steady state theory and which cannot beattributed to the AC Stark effect. Careful tests of both the experimental measurements and thetheoretical model showed that it is necessary to include the effects of velocity selective opticalpumping 2 in the calculations. When these effects were included by using a rate equationapproach, the theoretical strong field lineshapes were found to be in excellent agreement withexperiment. 3References1. R.E. Tench and S. Ezekiel, Chem. Phys. Lett. 96, 253 (1983).2. J.E. Bjorkholm, P.F. Liao, and A. Wokaun, "Distortion of On-Resonance Two-PhotonSpectroscopic Line Shapes Caused by Velocity-Selective Optical Pumping," Phys. Rev. A26, 2643 (1982).3. R.E. Tench and S. Ezekiel, to be published.20.2 Precision Experimental Studies of CollisionallyBroadened Lineshapes Using a Pump-Probe TechniqueNational Science Foundation (Grant PHY82-10369)Robert E. Tench, Shaoul EzekielWe have performed preliminary experimental studies of the effects of collisions on pump-probeinteractions in 12 vapor. These studies were carried out for 12 - 12 12 - He , 12 - Ar and 12 - Xecollisions in both weak and strong pump field limits. In the weak pump field case, strongnonlinear behavior was observed in pressure broadening curves for both the forward and thebackward scattered lineshapes. In the strong pump field case, an increase in height and adecrease in linewidth were observed for the backward scattered line when buffer gases wereadmitted to the 12 cell. Such lineshapes are expected to be very sensitive, high resolution probesof velocity and phase changing collisions in a vapor, and these studies are being pursued bothexperimentally and theoretically.20.3 Atom-Field interaction in Atomic BeamsNational Science Foundation (Grant PHY82 10369)Mara Prentiss, Shaoul EzekielWe have previously studied atom-field interaction using a traveling wave excitation field and aRLE P.R. No. 127 122Quantum Optics and Photonicssodium atomic beam " prepared as a two-level system. Our data showed that atomic recoilstrongly influenced the symmetry of the fluorescent lineshapes as the intensity of the excitationfield is increased. In order to reduce atomic recoil effects we have recently begun to investigatethe use of a standing wave rather than a traveling wave excitation.In this case, the fluorescence lineshapes also exhibited an asymmetry at strong fields whichcannot be explained by residual recoil effects. We attribute the observed symmetries in a strongstanding wave field to the atomic motion along the standing wave direction caused by the forceon the induced atomic dipoles in the field gradient of the standing wave. This effect is beingcarefully studied both theoretically and experimentally.References1. P.R. Hemmer, B.W. Peuse, F.Y. Wu, J.E. Thomas, and S. Ezekiel, "Precision Atomic-BeamStudies of Atom-Field Interactions," Opt. Lett. 6, 531 (1981).2. B.W. Peuse, R.E. Tench, P.R. Hemmer, J.E. Thomas, and S. Ezekiel, "Precision Studies in3-Level Systems," in A.R.W. McKellar, T. Oka, and B.P. Stoicheff (Eds.), LaserSpectroscopy V (Springer-Verlag 1981) p. 251.3. B.W. Peuse, M.G. Prentiss, and S. Ezekiel, "Distortion in Atomic Beam Absorption Lineshapes,"Journal de Physique, Colloque C8, Supplement au no 12, Tome 42, C8-53, December1981.4. B.W. Peuse, M.G. Prentiss, and S. Ezekiel, "Observation of Resonant Light Diffraction by anAtomic Beam," Phys. Rev. Lett. 49, 269 (1982).5. B.W. Peuse, M.G. Prentiss, and S. Ezekiel, "Elimination of Lineshape Distortion in LaserAbsorption Spectroscopy in Atomic Beams," Opt. Lett. 8, 154 (1983).20.4 Laser Raman Microwave ClockNational Science Foundation (Grant PHY82-10369)Joint Services Electronics Program (Contract DAAG29-83-K-0003)Philip H. Hemmer, Guy Ontai, Shaoul EzekielRecently, we have been investigating the possibility of developing an atomic clock based on alaser-induced resonance Raman transition. 1,4 The potential advantages of such a clock arisefrom the use of an all optical excitation, which eliminates the need for bulky and expensivemicrowave cavities and state selection magnets used in conventional atomic clocks. This shouldlead, for example, to the development of more accurate and more compact, portable cesiumbeam clocks.In earlier work, it was demonstrated that transit time limited Raman linewidths as narrow as 1.3kHz (FWHM) could be observed using a 1772 MHz resonance Raman transition in a sodiumatomic beam. These narrow transit time limited linewidths were obtained using Ramsey's methodof separated field excitation, in analogy with microwave techniques. To reduce laser jitter effects,an acousto-optic frequency shifter was used to generate one laser frequency directly from theRLE P.R. No. 127123Quantum Optics and Photonicsother, thereby insuring a highly stable laser difference frequency.To demonstrate clock applications, a microwave oscillator was stabilized to a 2.6 kHz wideRaman transition, obtained using a 15 cm Ramsey zone separation. The fractional frequencydeviation of the stabilized oscillator was as small as 1.5 x 10-11 for a 1000 sec averaging time.This stability, which is close to the shot noise limit of the present setup, compares favorably withcommercial cesium clocks when differences in transit time and transition frequency are taken intoconsideration.For longer averaging times, the stability is not as good, due to the presence of long-termfrequency errors. Potential sources of long-term frequency error studied recently include: (1) theeffects of relative misalignments of the two laser fields away from copropagating, (2) the effects ofbirefringence related optical phase shifts produced when the relative phases of the two laserfields are different at the two Ramsey interaction zones, (3) phase shifts produced by path lengthchanges on the scale of the effective microwave wavelength, (4) laser detuning effects, (5) theeffects of external magnetic fields, including the earth's field, (6) changes in atomic beamalignment, (7) laser beam misalignments (both frequencies together), (8) laser power, bothrelative and absolute and (9) the effects of other atomic levels near the intermediate state. Whilethese potential frequency error sources are still under study, much progress has already beenmade in order to achieve such stabilities at 1000 sec averaging times.Future plans include a more detailed study of potential long-term frequency error sources.Efforts are also in progress to improve the (shot noise limited) short term stability by increasingsodium beam throughout and to improve overall stability by extending the Ramsey zoneseparation out to 1 meter. Finally, we are preparing to construct an experimental Raman cesiumclock using a very simple atomic beam and employing semiconductor laser and fiber optictechnology. With such an experimental Raman cesium clock we hope to demonstrate potentialadvantages over conventional microwave cesium clocks.References1. J.E. Thomas, S. Ezekiel, C.C. Leiby, Jr., R.H. Picard, and C.R. Willis, Opt. Lett. 6, 298 (1981).2. J.E. Thomas, P.R. Hemmer, S. Ezekiel, C.C. Leiby, Jr., R.H. Picard, and C.R. Willis,"Observation of Ramsey Fringes Using a Stimulated Resonance Raman Transition in aSodium Atomic Beam," Phys. Rev. Lett. 4, 867 (1982).3. P.R. Hemmer, S. Ezekiel, and C.C. Leiby, Jr., "Stabilization of a Microwave Oscillator Using aResonance Raman Transition in a Sodium Beam," in W.D. Phillips (Ed.), Laser-Cooledand Trapped Atoms, Nat. Bur. Stand. (U.S.). Special Publication 653, June 1983, p. 47.4. P.R. Hemmer, S. Ezekiel, and C.C. Leiby, Jr., "Stabilization of a Microwave Oscillation Using aResonance Raman Transition in a Sodium Beam," Opt. Lett. 8, 440 (1983).5. P.R. Hemmer, S. Ezekiel, and C.C. Leiby, "Performance of a Microwave Clock Based on a LaserInduced Stimulated Raman Interaction," Technical Digest XIII, International QuantumElectronics Conference, June 18, 1984, p. 114.RLE P.R. No. 127 124Quantum Optics and Photonics20.5 Passive Resonator "Gyroscope"U.S. Air Force -Office of Scientific Research (Contract F49620-82-C-0091)Joint Services Electronics Program (Contract DAAG29-83-K-0003)Farhad Zarinetchi, Shaoul EzekielPrecision measurement of inertial rotation is of much interest in a number of areas, such asnavigation, geophysics, and relativity. The geophysical applications include the measurement ofthe various effects that cause fluctuations in the earth's rotation rate 2 E' ranging from 10 ' to10 -9 E' for example, nutation, precession, wobble, and tidal-friction effects. The relativisticeffects range in sensitivity from 10-9 to 10 - '' E and include measurements of the preferredframe and the drag parameters.The advent of the laser in 1960 rekindled the interest in the use of the Sagnac effect for sensinginertial rotation by optical means. Several approaches of implementing the Sagnac effect havebeen under investigation. These include active techniques, such as the ring laser gyro, andpassive techniques employing passive ring resonators15 or multiturn fiber-optic interferometers.In all these approaches, the measurement sensitivity scales with the area enclosed by the lightpath. Typically, to reach the sensitivity needed to measure the geophysical and relativistic effectsmentioned previously, it is necessary to consider areas between 102 and 104m 2 .Our research effort at present centers around a passive 10 cm square resonator with a Finesseof 12000 (kindly made available to us by Litton). The differences between the resonancefrequencies of the cavity for clockwise and counterclockwise propagation that is induced byinertial rotation is measured by a low power He-Ne laser mounted external to the cavity. So far wehave demonstrated excellent short term drift of 0.010/hr for averaging times of 100 seconds whichis consistent with the photon shot noise noise limit applicable to our set-up. In addition we havedemonstrated the cross-coupling between the counter propagating beams due to back scatterand showed how to eliminate such an effect. We are also studying various configurations forprobing such a resonator, in particular, the relative merits of observing the transmitted lightversus the reflected light.References1. G.A. Sanders, M.G. Prentiss, and S. Ezekiel, "Passive Ring Resonator Method for SensitiveInertial Rotation Measurements in Geophysics and Relativity." Opt. Lett. 6, 569 (1981).2. R.E. Meyer, G.A. Sanders, and S. Ezekiel. "Observation of Spatial Variations in the ResonanceFrequency of an Optical Resonator," J. Opt. Soc. Am. 73, 939 (1983).3. G. Sanders and S. Ezekiel, "Measurement of Fresnel Drag in Moving Media Using a RingResonator Technique," Technical Digest XIII, International Quantum ElectronicsConference June 18-21, 1984, p. 114.4. F. Zarinetchi. R.E. Meyer, G.A. Sanders, and S. Ezekiel, "Passive Resonator Gyro," Fiberopticand Laser Sensors, SPIE publication No. 478 (1984).RLE P.R. No. 127125Quantum Optics and Photonics5. S. Ezekiel, "An Overview of Passive Optical Gyros," Proceedinos of the Snowbird Conferenceon Optical RinQ Gyros, SPIE publication No. 487 (1984).20.6 Fiberoptic Ring Resonator "Gyroscope"U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)Roberto Shu, John Kierstead, Shaoul EzekielWe are investigating the use of an all-fiber ring resonator as a sensor of absolute rotation. 1-4The principle here is similar to that of the discrete mirror resonator method that has been underdevelopment in our laboratory for several years. In brief the mirror resonator is simply replacedwith a single mode fiber resonator and the input-output coupling is accomplished by means ofevanescent wave fiber couplers. The presence of rotation perpendicular to the plane of theresonator causes a difference in the frequencies of the resonator when observed along counterpropagating directions.To achieve high performance consistent with shot noise prediction a number of problems mustbe studied and solved. in particular we are studying the effects of cross coupling between thecounter propagating beams, fiber birefringence and non-linear phenomena such as the opticalKerr effect and stimulated Brilloun scattering.References1. R.E. Meyer and S. Ezekiel, "Fiberoptic Resonator Gyroscope," presented at the FirstInternational Conference on Optical Fiber Sensors, lEE, London, England, April 1983.2. R.E. Meyer. S. Ezekiel. D.W. Stowe, and V.J. Tekippe, "Passive Fiberoptic Ring Resonator forRotation Sensing." Opt. Lett. 8, 644 (1983).3. S. Ezekiel, "An Overview of Passive Optical "Gyros", Proceedings of the Snowbird Conferenceon Ontical Ring Gyros, SPIE No. 478 (1984).4. R.E. Meyer and S. Ezekiel, "High Finesse Fiber Ring Resonator for Rotation Sensing,"Technical Digest, Conference onr Fiberoptic Communication, OFC '84, January 23-25, p.42.20.7 Long-Term Wavelength Stabilization of BroadbandSemiconductor Light SourcesLitton Guidance and Control SystemHarty Chuu, Shaoui EzekielWork is under way to develop techniques for long-term stabilization of the average wavelengthof broadband semiconductor sources, for example, super luminescent diodes. in the 0.8 [tmwavelength range. These sources are important for minimizing coherent back-scattering andnon-linear index effects in fiber-optical interferometric rotation sen~ors that make use of theRLE P.R. No. 127 126Ouantum Optics and PhotonicsSagnac effect. We are currently pursuing an indirect stabilization scheme in which a Michelsoninterferometer is first stabilized with respect to a HeNe laser of known wavelength, and theinterferometer is then used to stabilize the semiconductor light source. The HeNe laser may bereplaced by a stabilized single frequency semiconductor laser for compactness and ruggedness.We are also considering the use of an integrated optic Mach-Zender interferometer with unequalarms as a reference with or without a stable secondary light source.In addition, a number of characteristics of broadband semiconductor sources are beinginvestigated. These include the optical spectrum, the noise spectrum, and the shift of the averagewavelength with temperatures and injection current.20.8 Linewidth Reduction and Stabilization of SingleFrequency Semiconductor LasersJoint Services Electronics Program (Contract DAAG29-83-K-0003)Sudhanshu Jain, John Kierstead, Shaoul EzekielSingle frequency semiconductor lasers have inherently a broad linewidth as compared with gaslasers. Considerable effort has gone into the study of the properties of these lasers and thedevelopment of methods for the reduction of the laser linewidth.1.2At present we are exploiting the simple techniques of linewidth narrowing by optical fe-edbackfrom an external mirror. The magnitude of linewidth reduction depends on both the magnitudeand phase of the light feedback into the laser. In addition to linewidth narrowing, we are alsoevaluating various schemes for the stabilization of the phase of the optical feedback so as tomaintain narrow linewidth operations.References1. R. Lang and K. Kobayashi, "External Optical Feedback Effects on Semiconductor InjectionLaser Properties," IEEE. J. Quant. Electron. ClE-16, 3, March 1980.2. G.A. Acket, D. Lenstra, A.J. denBoef, and B.H. Verbeek. "The Influence of Feedback Intensityon Longitudinal Mode Properties and Optical Noise in Index-Guided SemiconductorLasers," IEEE J. Quant. Electron. QE-20, 10, October 1984.20.9 Optical Phase Conjugation in a Ring ResonatorNational Science Foundation (Grant PHY82-10369)Bertrand Kleinmann, Shaou! EzekielUsed in a four-wave mixing configuration, a non-linear medium may have a reflection and atransmission coefficient higher than one.' Therefore, we should be able to observe a coherentRLE P.R. No. 127127Quantum Optics and Photonicsoscillation in a ring resonator containing such a medium. We plan to study the variouscharacteristics of the emitted light as a function of the direction of propagation and of any kind ofreciprocal or non-reciprocal phase shifts that could be experienced by the light in the resonator.Aside from fundamental interest, such research may be of use in the development of verysensitive optical rotation sensors based on the Sagnac effect2 and in the generation andobservation of "squeezed states".References1. B. Kleinmann, Ph.D. Thesis, Ecole Normale Superieure, Paris, France, June 1984.2. M.M. Tehrani, "The Phase Conjugate Ring Laser Gyro (P *RLG)," SPIE No. 412 (1983).RLLE P.R. No. 127 128

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