Contains reports on seven research projects.Air Force Rome Air Development Center (in collaboration with C.C. Leiby, Jr.)U.S. Air Force-Rome Air Development Center (Contract F19628-80-C-0077)National Science Foundation (Grant PHY79-09739)Joint Services Electronics Program (Contract DAAG29-80-C-0104)U.S. Air Force Geophysics Laboratory (Contract F19628-79-C-0082

DiFillipo, David

Ezekiel, Shaoul

Hemmer, Philip R.

Kierstead, John D.

Meyer, Raymond E.

Peuse, Bruce W.

Ponikvar, Donald R.

Prentiss, Mara G.

Sanders, Glen A.

Tench, Robert E.

DSpace@MIT

Photonics8. PhotonicsAcademic and Research StaffProf. S. Ezekiel, J. KiersteadGraduate StudentsD. DiFillipo, P.R. Hemmer, R.E. Meyer, B.W. Peuse, D.R. Ponikvar, M.G. Prentiss,G.A. Sanders, R.E. Tench8.1 Ultrahigh-Resolution Spectroscopy and FrequencyStandards in the Microwave and MM Wave Regions UsingOptical LasersAir Force Rome Air Development Center (in collaboration with C.C. Leiby, Jr.)U.S. Air Force -Rome Air Development Center (Contract F19628-80-C-0077)Philip R. Hemmer, Shaoul EzekielIn this program we are considering an attractive possibility for obtaining ultrahigh resolution in themicrowave and mm regions using optically induced Raman transitions in atomic beams. Theresearch is centered around the interaction of two laser fields with a three level system in an atomicbeam. Of particular interest is the basic study of coherent two-photon excitations in a folded threelevel system in which exceedingly narrow resonances can be obtained when the initial and final levelsare long lived states. As is well known, the linewidth is determined only by the initial and final leveldecay rates for a Doppler Free system such as an atomic beam.In order to achieve such narrow linewidths, laser frequency jitter must be eliminated and the timethe atom spends in the excitation field must be made as long as possible to reduce the transit timelinewidth. We eliminate laser jitter by correlating the jitter in the two lasers since the transitionfrequency of interest depends on the difference in the laser frequencies. In summary, we are able tomake a transition from the first level to the final level indirectly via the intermediate level and achieve alinewidth equivalent to that obtained by a direct transition from the first to the final level using amicrowave or mm wave source.Our initial experiments have been conducted with an atomic beam of sodium and dye lasers. In thiscase the difference in the laser frequencies is 1772 MHz. Laser jitter in each beam was correlated bysimply deriving one laser frequency from the other by an acousto-optic frequency shifter driven at1772 MHz. A linewidth of 650 Hz was achieved by using Ramsey's separated oscillator method with a30 cm separation between the interaction regions. We have also stabilized the 1772 MHz oscillator toRLE P.R. 125Photonicsthe Ramsey resonance and achieved a stability of 5.6 x 10'11 for an averaging time of 100 seconds.Future work is concerned with the study of level shifts in the resonance Raman scheme whichinfluence the ultimate performance of such a stabilization system. In addition we are consideringvarious techniques for cooling the Na Beam so as to achieve narrower transit time linewidths.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, "Observationof Ramsey Fringes Using a Stimulated Resonance Raman Transition in a Sodium AtomicBeam," Phys. Rev. Lett. 4, 867 (1982).3. P.R. Hemmer, S. Ezekiel, and C.C. Leiby, Jr., "Stabilization of a Microwave Oscillation Using aResonance Raman Transition in a Sodium Beam," in W.D. Phillips (Ed.), Laser-Cooled andTrapped 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., August 1983, to be published.8.2 Resonant Light Diffraction by an Atomic BeamNational Science Foundation (Grant PHY79-09739)Joint Services Electronics Program (Contract DAAG29-80-C-0104)Bruce W. Peuse, Mara G. Prentiss, Shaoul EzekielWe have observed resonant light diffraction by an atomic beam of 2-level sodium atoms. This grewout of an effort to develop new techniques of performing absorption spectroscopy in low densityatomic beams, that are capable of achieving quantum noise limited sensitivity. As a result of usingsuch techniques, we found that the absorption lineshape exhibited an asymmetry even for weak fieldsand the magnitude of this asymmetry depended on the position and size of the detector. In contrast,the lineshape determined by collecting the fluorescence for the same atoms did not exhibit anyasymmetry. Moreover, we measure the on-resonance and also the off-resonance absorption as afunction of detector position.We explain the observed distortion in the absorption lineshape and the spatial absorption behavioras a manifestation of the interference between light scattered by the atoms with the excitation beamat a given position of the detection plane. In other words, we have observed a diffraction-like patterndue to the laser beam propagating across a thin atomic beam. The difference between on-resonanceand off-resonance behavior is explained by the dependence of the phase of the scattered field onfrequency. Our calculations are in good agreement with the experimental data.The above diffraction phenomena along with the resulting lineshape distortion can be eliminated byplacing the detector very close to the interaction region, but this is clearly not feasible. However, it isRLE P.R. 125Photonicspossible to achieve the same results by imaging the fields in the interaction region at the detectionplane. In our experiment this was accomplished by placing two lenses of equal focal length f in thelaser beam after the interaction region. In this way, the fields in the interaction region are faithfullyreproduced at the image or detection plane. When the apertured detector is scanned along theimage plane while the laser is held on resonance, the spatial pattern that results no longer shows anydiffraction behavior. Moreover, the lineshape distortion was also eliminated by using this imagingtechnique.References1. B.W. Peuse, M.G. Prentiss, and S. Ezekiel, "Distortion in Atomic Beam Absorption Lineshapes,"Journal de Physique Colloque C8, Supplement au n'12, Tome 42, C8-53, December 1981.2. B.W. Peuse, M.G. Prentiss, and S. Ezekiel, "Observation of Resonant Light Diffraction by anAtomic Beam," Phys. Rev. Lett. 49, 269 (1982).3. B.W. Peuse, M.G. Prentiss, and S. Ezekiel, "Elimination of Lineshape Distortion in LaserAbsorption Spectroscopy in Atomic Beams," Opt. Lett. 8, 154 (1983).8.3 Precision Atomic Beam Studies of Atom-Field InteractionsNational Science Foundaton (Grant PHY79-09739)Joint Services Electronics Program (Contract DAAG29-80-C-0104)Bruce W. Peuse, Mara G. Prentiss, Shaoul EzekielThe interaction of radiation with two and three level quantum mechanical systems is of muchinterest because it involves basic processes. So far we have studied the interaction of 2-level and3-level sodium atoms with one and also with two monochromatic fields provided by stable, singlefrequency dye lasers. One laser acts as the pump and interacts primarily with two of the levels. Thesecond laser then probes the absorption between either one of these levels to a third level. In thisway, we have studied a cascade system, a Vee system and also an inverted Vee system. In the case ofa weak pump field, our probe data was in very good agreement with theoretical calculations.However, when the pump was made very intense the probe data could not be explained by the a.c.stark effect alone. Atomic recoil had to be included in the calculations in order to explain thepeculiarities observed.References1. R.E. Tench, B.W. Peuse, P.R. Hemmer, J.E. Thomas, and S. Ezekiel, "Two Laser Raman DifferenceTechniques Applied to High Precision Spectroscopy," Journal de Physique, Colloque C8,Supplement au n0 12, December 1981.2. P.R. Hemmer, B.W. Peuse, F.Y. Wu, J.E. Thomas, and S. Ezekiel, "Precision Atomic-Beam Studiesof Atom-Field Interactions," Opt. Lett. 6, 531 (1981).3. B.W. Peuse, R.E. Tench, P.R. Hemmer, J.E. Thomas, and S. Ezekiel, "Precision Studies in 3-LevelSystems," in A.R.W. McKellar, T. Oka, and B.P. Stoicheff (Eds.), Laser Spectroscovy V(Springer-Verlag 1981) p. 251.RLE P.R. 125Photonics8.4 Measurement of Natural Predissociation Effects in IodineMoleculesJoint Services Electronics Program (Contract DAAG29-80-C-0104)National Science Foundation (Grant PHY79-09739)Robert E. Tench, Donald R. Ponikvar, Shaoul EzekielIn our continuing study of the interaction of two monochromatic fields with folded 3-level systemsin vapors, we have performed extremely high resolution measurements of Doppler free resonances in12. With weak copropagating pump and probe fields we have observed linewidths as narrow as 50kHz, vapors, we have performed extremely high resolution measurements of Doppler free resonancesin 12. With weak copropagating pump and probe fields we have observed linewidths as narrow as 50kHz, determined, in principle, by the relaxation rates of the first and final levels with a smallcontribution from the relaxation rate of the intermediate level. For counterpropagating fields we haveobserved a probe linewidth of about 150 kHz that is determined primarily by twice the relaxation rateof the intermediate level. We are using this doubling of the intermediate level relaxation rate toperform precision measurements of the nature linewidths of the many hyperfine transitions in theP(13) 43-0 and R(15) 43-0, B-X transitions at 5145 A. Because of natural predissociation effects inthe 12 molecule, the natural width of each hyperfine component will be different. Our precisionmeasurements will therefore enable us to study in more detail such predissociation phenomena.Since molecular iodine is being considered as a reference molecule in the visible region of thespectrum, precision linewidth and lineshape measurements of individual hyperfine components aswell as the spacing between components is of much interest.References1. R.E. Tench, B.W. Peuse, P.R. Hemmer, J.E. Thomas, and S. Ezekiel, "Two Laser Raman DifferenceTechniques Applied to High Precision Spectroscopy," Journal de Physique, Colloque C8,Supplement au n°12, Tome 42, December 1981.2. R.E. Tench and S. Ezekiel, "Precision Measurements of Hyperfine Predissociation in 12 VaporUsing a Two-Photon Resonant Scattering Technique," Chem. Phys. Lett., to be published.8.5 Passive Ring Resonator Method for Sensitive InertialRotation Measurements in Geophysics and RelativityU.S. Air Force Geophysics Laboratory (Contract F19628-79-C-0082)Glen A. Sanders, Raymond E. Meyer, John Kierstead, 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 of theRLE P.R. 125Photonicsvarious effects that cause fluctuations in the earth's rotation rate 0 E, ranging from 10.7 to 10-99F, forexample, nutation, precession, wobble, and tidal-friction effects. The relativistic effects range insensitivity from 10. 9 to 10"11 E and include measurements of the preferred frame and the dragparameters.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 to implementing the Sagnac effect have beenunder investigation. These include active techniques, such as the ring laser gyro, and passivetechniques employing passive ring resonators or multiturn fiber-optic interferometers. In all theseapproaches, the measurement sensitivity scales with the area enclosed by the light path. Typically, toreach the sensitivity needed to measure the geophysical and relativistic effects mentioned previously,it is necessary to consider areas between 102 and 104 m2.Our research effort centers around the passive resonator technique. Our present setup is a squarecavity, 70 cm on a side, mounted on a super invar table. The difference between the resonancefrequencies of the cavity for clockwise (cw) and counterclockwise (ccw) propagation induced byinertial rotation is measured by a 1/2-mW He-Ne laser, mounted external to the cavity. We havereduced the short-term random drift to about 3 x 10-4 E (where 2 E is earth rotation rate) in anaveraging time of 30 seconds which is close to the photon shot noise limit in our setup. The study oflong-term drift is in progress.References1. G.A. Sanders, M.G. Prentiss, and S. Ezekiel, "Passive Ring Resonator Method for Sensitive InertialRotation 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. of Am., to be published.8.6 Closed Loop, Low Noise Fiberoptic Rotation SensorJoint Services Electronics Program (Contract DAAG29-80-C-0104)U.S. Air Force - Rome Air Development Center (Contract F19628-80-C-0077)David Di Fillipo, Mara G. Prentiss, Shaoul EzekielThe fiberoptic gyroscope has been receiving considerable attention for the past several years. Anumber of different approaches have been studied, and as these studies progress a number ofproblems were uncovered.Our present approach employs a 200 m long fiber wound around a 19 cm diameter spool andoperated in a closed loop mode. Our measurement approach is based on the use of twoacousto-optic frequency shifters placed within the fiber interferometer for providing nonreciprocalRLE P.R. 125Photonicsphase modulation as well as nonreciprocal frequency offsets needed in closed loop operation.Short-term random drift is about 0.03 0/hr for averaging times of 30 seconds which is close to thatpredicted by the photon shot noise limit in our setup. The long-term performance departs from thephoton noise limit and considerable effort is at present directed into the sources of long-term drift. Inthis connection, we have predicted and observed an intensity-induced nonreciprocity in thefiberoptic gyro. We found that a nonreciprocal phase shift of 1.4 x 10.6 radians can be generated by aone microwatt power difference between the oppositely propagating light beams. Our fiber is 200 mlong with a core diameter of 4.5 microns, and wound on a 19 cm diameter spool. The intensitydependent nonreciprocal phase shift, which is attributed to a four wave mixing process in the quartzmedium, is equivalent to a rotation rate of 0.20 /hr in the present geometry, and therefore stresses theneed for a strict intensity control in precision fiber rotation sensors.References1. J.L. Davis and S. Ezekiel, "Closed Loop, Low Noise Fiberoptic Rotation Sensor," Opt. Lett. 6, 505(1981).2. M.G. Prentiss, J.L. Davis, and S. Ezekiel, "Closed Loop, High Sensitivity Fiber Gyroscope," inS. Ezekiel and H.J. Arditty (Eds.), Fiberoptic Rotation Sensors (Springer-Verlag 1982).3. S. Ezekiel, J.L. Davis, and R.W. Hellwarth, "Observation of Intensity-Induced Nonreciprocity in aFiberoptic Gyroscope," Opt. Lett. Z, 457 (1982).8.7 Fiberoptic Ring Resonator GyroscopeU.S. Air Force Geophysics Laboratory (Contract F19628-79-C-0082)Joint Services Electronics Program (Contract DAAG29-80-C-0104)Raymond E. Meyer, John Kierstead, Shaoul EzekielIn addition to the fiber interferometer method described in the previous section we are alsoinvestigating the use of an all-fiber ring resonator as a sensor of absolute rotation. The principle hereis similar to that of the discrete mirror resonator method that has been under development in ourlaboratory for several years. In brief, the mirror resonator is simply replaced with a single mode fiberresonator and the input-output coupling is accomplished by means of a fused evanescent wave fibercoupler. At present the finesse of the 3 meter fiber resonator is 140. Preliminary data on short-termnoise is about 0.50/hr (7 = 1 second) (rms) which is 10 times greater than the shot noise limit in ourpresent setup.References1. R.E. Meyer and S. Ezekiel, "Fiberoptic Resonator Gyroscope," presented at First InternationalConference on Optical Fiber Sensors, lEE, London, England, April 1983.RLE P.R. 125

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