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

Chou, Harry

Ezekiel, Shaoul

Hemmer, Philip H.

Hergenroeder, Leo

Jain, Sudhanshu H.

Keirstead, John

Kleinmann, Bertrand

Natoli, Vincent

O'Connor, Chris

Ontai, Guy P.

Pevtschin, Veronique

Prentiss, Mara G.

Rockoff, Lisa

Shahriar, M. Selim

Smith, Stephen P.

Zarinetchi, Farhad

DSpace@MIT

Quantum Optics and Photonics21. Quantum Optics and PhotonicsAcademic and Research StaffProf. S. Ezekiel, Dr. B. Kleinmann, Dr. P.R. Hemmer, J. KiersteadGraduate StudentsH. Chou, L. Hergenroeder, S.H. Jain, F. Long, V. Natoli, C. O'Connor, G. Ontai,V. Pevtschin, M.G. Prentiss, S. Shu, R.E. Tench, E. Young, F. ZarinetchiUndergraduate StudentsL. Rockoff, S. Miller, M. S. Shahriar, S. Smith, I. Robinson, R. Rizk21.1 Precision Studies of Stimulated Resonance RamanInteractions in an Atomic BeamU.S. Air Force - Office of Scientific Research (Contract F49620-82-C-009 1)Joint Services Electronics Program (Contract DAAG29-83-K-0003)Philip H. Hemmer, Guy P. Ontai, Vincent Natoli, Shaoul EzekielPrecision studies of stimulated resonance Raman interactions in a sodium atomic beam havebeen performed with emphasis on Ramsey's separated field excitation. Ramsey fringes wereobtained for a field separation of up to 30 cm, and the data were consistent with theoreticalpredictions. Possible applications of this Raman interaction to clock development have also beenstudied by stabilizing a microwave oscillator to a Raman/Ramsey fringe. The resulting oscillatorstability of 1.5 x 10- 1 1 for a 1000 second averaging time compares favorably with commercialcesium clocks when differences in atom transit time and transition frequency are taken intoconsideration. Finally, potential sources of long term frequency error which are important forclock applications have also been partially investigated.PublicationsHemmer, P.R., G.P. Ontai, and S. Ezekiel, "Precision Studies of Stimulated Resonance RamanInteractions in an Atomic Beam," J. Opt. Soc. Am. B, March 1986, to be published.21.2 Observation of Lineshape Asymmetry for a Two-LevelAtom in a Standing Wave FieldNational Science Foundation (Grant PHY82-10369)Joint Services Electronics Program (Contract DAAG29-83-K-0003)Mara G. Prentiss, Shaoul EzekielRLE P.R. 128139Quantum Optics and PhotonicsWe have observed intensity dependent asymmetries in the fluorescence lineshape of a two levelsodium atomic beam in the presence of either a travelling or a standing wave excitation field. Theasymmetry in the travelling wave case has been noted previously and is due predominantly to therecoil that the atoms experience in traversing the excitation field. We attribute the observedasymmetries in the standing wave field to the force experienced by the induced atomic dipoles inthe field gradient of the standing wave. Our calculations agree well with our data.Such lineshape studies are of much interest because of the important information they conveyabout basic atom field interactions and also because such lineshape asymmetries can influencethe accuracy of frequency/wavelength standards as well as the ultimate precision ofspectroscopic measurements.PublicationsPrentiss M.G., and S. Ezekiel, "Observation of Intensity Dependent Fluorescence LineshapeAsymmetry for Two-Level Atoms in a Standing Wave Field," Phys. Rev. Lett. 56, 46 (1986).21.3 Observation of Lock-in Behavior in a Passive ResonatorGyroscopeJoint Services Electronics Program (Contract DAAG29-83-K-0003)Farhad Zarinetchi, Shaoul EzekielA passive resonator rotation sensor or "gyroscope" is a ring resonator in which counterpropagating light beams within the resonator experience a nonreciprocal phase shift due to anapplied rotation rate. Because of this nonreciprocal phase shift the resonance frequencies of theresonator for counter propagating fields are not identical. This difference in resonancefrequency, A f, is measured by means external to the resonator, e.g., by locking the frequenciesof external laser beams to corresponding resonances of the cavity.Our research demonstrated that because of backscattering within the cavity, the difference inresonance frequency A f cannot be determined as long as A f is below a certain value which isset by the degree of backscattering. This behavior which is called "lock-in" has long beenobserved in ring laser gyros where a laser amplifier is placed within the resonator. In our passiveapproach lock-in occurs if all the information about backscattering is fed faithfully to the servoloops which hold the external laser frequencies to the cavity resonance.Lock-in was observed using mechanical rotation and also nonmechanical rotation, e.g., bysweeping the frequency of one of the external lasers. The theory of lock-in relative to our passiveresonator set-up was developed and used to understand the observed behavior in theneighborhood of lock-in. Finally, we demonstrated several nonmechanical schemes ofeliminating lock-in in a passive resonator gyro.RLE P.R. 128 140Quantum Optics and PhotonicsPublicationsZarenetchi F., and S. Ezekiel, "Observation of Lock-in Behavior in a Passive ResonatorGyroscope," Opt. Lett., June 1986, to be published.21.4 Fiber Ring Resonator "Gyroscope"Joint Services Electronics Program (Contract DAAG29-83-K-0003)Litton Guidance and Control SystemChris O'Connor, M. Selim Shahriar, Lisa Rockoff, John Kierstead, Shaoul EzekielWe are continuing our investigation of an all-fiber ring resonator as a sensor of absoluterotation. The principle here is similar to that of the discrete mirror resonator method that hasbeen under development in our laboratory for several years. In brief, the mirror resonator isreplaced with a single mode fiber resonator and the input-output coupling is accomplished byevanescent wave fiber couplers. The presence of rotation perpendicular to the plane of theresonator causes a difference in the frequencies of the resonator when observed alongcounterpropagating directions.We have studied a number of problem areas such as back-scattering, fiber birefringence andnonlinear phenomena such as the optical Kerr effect. In addition, we have constructed ahomemade polarization holding resonator to eliminate birefringence effects but the finesse of thisresonator has been low, so far, around 10, due to coupler losses.21.5 Fiber Interferometer GyroscopeJoint Services Electronics Program (Contract DAAG29-83-K-0003)Litton Guidance and Control SystemLeo Hergenroeder, Stephen Smith, John Kierstead, Shaoul EzekielIn a multiturn fiber interferometer gyroscope a broadband light source, e.g., a superluminescentdiode (SLD), is used to reduce any undesirable backscatter and also the optical Kerr effect.However, SLDs do not produce a lot of power and their lifetime is limited because they operate ata much higher current density than semiconductor lasers.We are investigating the use of a chirped frequency semiconductor laser to produce aneffectively broad width so as to replace the SLD. The frequency of a semiconductor laser may bechirped by varying the injection current. A number of techniques for chirping the laser are beingstudied with emphasis on the effect of mode hopping and on any broadband noise created by thechirping.RLE P.R. 128141Quantum Optics and Photonics21.6 Wavelength Stabilization of Broadband SemiconductorLight SourcesLitton Guidance and Control SystemHarry Chou, Shaoul EzekielBroadband semiconductor light sources, e.g., superluminescent diodes (SLDs) have beensuggested for use in fiberoptic rotation sensor to reduce the noise arising from backscattering inthe fiber and from the optical Kerr effect. For precision rotation sensing, the wavelength of such asource must be stabilized to about 1 part in 106 since the scale factor of the sensor involves thesource wavelength.Since the spectral width of SLDs is extremely wide in the neighborhood of 10 nm and alsoasymmetric, conventional stabilization schemes based on molecular absorption are not veryuseful. The scheme we developed is based on the use of a 2-beam interferometer technique inwhich the average wavelength of the broadband source is stabilized to a short path difference in aMichelson interferometer. This path difference is held fixed by stabilizing it to the wavelength of astable laser. Using such a technique we demonstrated a stability of the SLD wavelength to betterthan one part in 106 in an averaging time of 1 second. If the Michelson interferometer wereconstructed on an integrated optic chip the reference laser could be dispensed with. Thisscheme has the merit of being easily extendible to any wavelength regime.PublicationsChen H., and S. Ezekiel, "Wavelength Stabilization of Broadband Semiconductor Light Sources,"Opt. Lett. 10, 612 (1985).21.7 Stabilization of External Optical Feedback Phase in aSemiconductor LaserJoint Services Electronics Program (Contract DAAG29-83-K-0003)Litton Guidance and Control SystemSudhanshu H. Jain, Shaoul EzekielNarrow spectral output semiconductor lasers are important for heterodyne opticalcommunication systems, optical sensors and spectroscopy. The laser linewidth is typically 30MHz depending on the output power.One method of reducing the laser linewidth is by applying optical feedback from an externalmirror. The degree of linewidth reduction depends strongly on both the magnitude and phase ofthe optical feedback. Therefore both these quantities must be controlled to achieve and maintaina narrow laser linewidth.RLE P.R. 128 142Quantum Optics and PhotonicsWe have investigated a simple scheme of stabilizing the phase of optical feedback based on theasymmetric response to feedback phase at the two laser facets. Using such a scheme, wereduced the laser linewidth to much less than 1 MHz and held it at that value.PublicationsJain, S.H., and S. Ezekiel, "Stabilization of External Optical Feedback Phase in a SemiconductorLaser," Electron. Lett. 21, 957 (1985).21.8 Frequency Stabilization of a Semiconductor LaserU.S. Air Force - Office of Scientific Research (Contract F49620-82-C-009 1)Litton Guidance and Control SystemVeronique Pevtsrhin, Shaoul EzekielSingle frequency semiconductor lasers are now easily available and are being considered for anumber of applications such as communication, wavelength multiplexing, sensors, spectroscopy,and so on. The long term stability of the frequency of the laser is important in a number of suchapplications.We have performed a study of a simple scheme for the frequency stabilization of a simplesemiconductor laser. The laser is a single frequency Hitachi HLP 1400 operating at 0.82 im witha linewidth of about 30 MHz at a few mW of power. Long term stabilization was accomplished bylocking the laser frequency to the center of a 1.2 GHz wide absorption line in H20 vapor. Astability of about one part in 109 for an averaging time of one second was achieved which wasclose to the theoretical shot-noise limit. The scheme is straightforward and does not requireprecision alignment procedures. The performance was measured using an independent H20vapor cell. Intensity shifts were negligible but temperature dependent pressure shifts weremeasured as 3 MHz/ 0 C at room temperature and 1 MHz/' C at 0O C. Since water vapor has manytransitions in the near infrared, this simple stabilization system should be very useful.PublicationsPevtschin V., and S. Ezekiel, "Performance of a H20 Stabilized Semiconductor Laser," inpreparation.21.9 Observation of Bidirectional Emission in aPhase-Conjugate Ring ResonatorJoint Services Electronics Program (Contract DAAG29-83-K-0003)Bertrand Kleinmann, Shaoul EzekielOptical Phase-Conjugate Ring Resonators have been proposed to develop a "squeezed statesgenerator" as well as a new type of rotation sensor. 1' 2RLE P.R. 128143Quantum Optics and PhotonicsVarious experiments have been performed using atomic vapors as the non-linear medium butthey require the use of tunable lasers and it is very difficult to achieve high phase-conjugatereflectivities.3By using a BaTiO 3 crystal as the non-linear medium, it is very easy to obtain reflectivities higherthan one (that is to say higher than 100%) when it is pumped by an Argon laser.4 By placing thecrystal in a ring cavity we were able, for the first time to our knowledge, to observe a bidirectionalemission of light in the cavity. The previous reported results mentioned only unidirectionalemissions of light that were due to two-beam coupling in the crystal.5 In our case, one of theemitted beams was mainly due to that effect but the other one was generated by four-wave mixingand was therefore the phase-conjugate of the first one.Unfortunately it was not possible to stabilize the set-up well enough to obtain a steady emissionand a more detailed study of the crystal itself is necessary before it is possible to go forward in thecavity experiment. As a matter of fact, we observed that a single beam of light can bephase-conjugated by the crystal with no additional pump-beam. That "self-pumpedphase-conjugate mirror" can reach reflectivities up to 30% depending on the angle of incidenceof the light. We used such a "self-pumped phase-conjugate mirror" in a Michelson-likeinterferometer and we observed a beat note in the output showing that the phase-conjugatebeam is frequency shifted with respect to the laser beam. That effect can be understood in termsof moving gratings 6 but it clearly shows that a better understanding of the photorefractive crystalsthemselves is necessary before it is possible for anyone to perform precise experiments using thatmaterial.References1. A. Heidmann, Ph.D. Thesis, Ecole Normale Superieure, Paris, France, March 1984.2. M.M. Tehrani, "The Phase-Conjugate Ring Laser Gyro," SPIE no. 412, 1983.3. B. Kleinmann, Ph.D. Thesis, Ecole Normale Superieure, Paris, France, June 1984.4. J. Feinberg and R.W. Hellwarth, Opt. Lett. 5, 519 (1980).5. J.P. Huignard, Opt. Comm. 38, 249 (1981).6. P. Gunter et al., Opt. Comm. 55, 210 (1985)RLE P.R. 128 144

Quantum Optics and Photonics

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