Contains table of contents for Part II, table of contents for Section 1, and reports on six research projects.Charles S. Draper Laboratories Contract DL-H-418468U.S. Air Force - Electronic Systems Division Contract F19628-89-K-0300U.S. Navy - Office of Naval Research Grant N0014-91-J-1808U.S. Air Force - Electronic Systems Division Contract F19628-89-K-003

Donoghue, John J.

Ezekiel, Shaoul

Hemmer, Philip R.

Kierstead, John D.

McCabe, Margaret M.

Prentiss, Mara G.

Shahriar, M. Selim

Smith, Stephen P.

Snitzer, Elias

Zarinetchi, Farhad

Contains table of contents for Part II, table of contents for Section 1 and reports on three research projects.Rome Air Development CenterCharles S. Draper Laborator

DSpace@MIT

I Physicsi1 Atomic, Molecul,Physics:tion 2 FhysicSectionSectionr and :ical128 RLE Progress Report Number 132Section 1 Atomic,PhysicsMolecular and OpticalChapter 1Chapter 2Chapter 3Quantum Optics and PhotonicsBasic Atomic PhysicsSmall Angle X-Ray and Neutron Scattering -Its Application to Supramolecular Solutions129130 RLE Progress Report Number 132Chapter 1. Quantum Optics and PhotonicsChapter 1. Quantum Optics and PhotonicsAcademic and Research StaffProfessor Shaoul Ezekiel, Dr. Mara G. PrentissVisiting Scientists and Research AffiliatesDr. Philip R. Hemmer, John Kierstead, Dr. Elias Snitzer'Graduate StudentsM. Selim Shahriar, Stephen P. Smith, Farhad Zarinetchi, John DonoghueTechnical and Support StaffMargaret McCabe1.1 Microwave PhaseDependent Optical AbsorptionSponsorRome Air Development CenterA laser excited resonant Raman interactioncauses atoms to be optically pumped into anon-absorbing dressed state, called thetrapped state.2 We have shown how a micro-wave field can modify this non-absorbingstate in a phase sensitive way to producechanges in the absorption of the opticalRaman excitation fields.Figure 1 shows a three-level atomic systemin the lambda configuration, where wo and 02are the frequencies of the laser fields whichexcite the Raman transition, and w3 is thefrequency of the microwave field. Here it isassumed that states 1 and 3 are long-lived,but state 2 is short-lived with a decay rate ofy2 . The Raman trapped state has the form[I1 > Iol > - 13 > 1w2 > ]/2,where equal Rabi frequencies have beenassumed, and Iwo > and (02> are singlephoton states. In comparison, the high andlow energy dressed states of the singlephoton 1 (4 3 microwave transition are[11 > 13 > - 13 > ]/Jand[El1 > 1w3 > + 13 > ]/ ,_D Y12>bW IWFigure 1. Three level atomic system showing reso-nance Raman excitation fields o) and 02 and micro-wave field 0)2.1 Rutgers University, New Jersey.2 H.R. Gray, R.M. Whitley, and C.R. Stroud, Jr., "Coherence Trapping of Atomic Populations," Opt. Lett. 3:218(1978).131Chapter 1. Quantum Optics and PhotonicsFigure 2. Schematic of experimental setup.respectively.3When the laser difference frequency c, - 2is exactly in (or out of) phase with themicrowave frequency o2, the Raman trappedstate translates directly into the high (or low)energy microwave dressed state. For anyother value of phase difference, a linear com-bination of microwave dressed states results.In this case, the microwave interaction par-tially destroys the Raman trapped state,resulting in increased optical absorption.Thus, the optical absorption is sensitive tomicrowave phase.To observe this effect, we used a three-zonesodium atomic beam apparatus as illustratedschematically in figure 2. Here the inter-action in zone A optically pumps the sodiumatoms into the Raman trapped state. Theseprepared atoms then interact with a micro-wave field inside the cavity (zone M) and thechanges in optical absorption are monitoredin zone B via fluorescence induced with aRaman probing interaction. With no micro-wave field, the Raman-Ramsey fringelineshape of figure 3a is observed.4 However,when microwave power corresponding to ait-pulse is present in zone M, the lineshapeof figure 3b results. The oscillations shownby this data are produced by a rapid scan-ning of the relative microwave and laser dif-ference frequency phases via the PZT (figure2). Large changes in optical absorption areproduced by changing only the relative phaseof the microwave field. Figure 3c shows thecorresponding theoretical lineshape whichincludes the effect of velocity averaging inthe atomic beam. The preliminary datashows qualitatively good agreement betweentheory and experiment.There would be many applications for thistechnique if the microwave transition couldbe replaced by a mm-wave or FIR transition.For example, if a mm-wave or FIR beam anda double optical beam intersect at an angle,the resulting spatial dependence of the rela-tive phase would produce a grating-likediffraction of both beams. This doublediffraction effect may have applications inbeam steering and, possibly, in convertingreal time holographic images.1.2 A New Approach toMicrowave Excitation ofAtomic BeamsA beam of alkali atoms, e.g., sodium, initiallystate-prepared into one of the ground statehyperfine levels, undergoes Rabi floppingwhen passed through a microwave cavityexcited by a resonant microwave frequency.5Figure 4, plot I, shows how the amplitude ofthe oscillating B field is usually configured inthe cavity. The population change ismaximum when the microwave field strengthcorresponds to a i-pulse for the transit time.If the microwave frequency is scanned, thefamiliar Lorentzian lineshape (figure 5a,dashed line) is observed, its linewidth deter-mined by transit time and power broadening.Figure 4, plot II, shows that, if the field3 Y.S. Bai, A.G. Yodh, T.W. Mossberg, "Selective Excitation of Dressed Atomic States by Use of Phase-ControlledOptical Fields," Phys. Rev. Lett. 55:1277 (1985).4 J.E. Thomas, P.R. Hemmer, S. Ezekiel, C.C. Leiby, Jr., R.H. Picard, and C.R. Willis, "Observation of RamseyFringes Using a Stimulated, Resonance Raman Transition in a Sodium Atomic Beam," Phys. Rev. Lett. 48:867(1982).5 N.F. Ramsey, Molecular Beams. (London: Oxford University Press, 1956).132 RLE Progress Report Number 132!UE1'- I---I--- - ----~--- - I------ - ---------- --.I .~ --- -'' ''~~ "~~:...... : ~"':: .I:-"'---+;- -"" "~L'~"'IC' ~-r ~- --- I... i~ ' ' ' ' ' ' ' ' '"""" ~~'w- 2Figure 3. (a) Data showing Raman-Ramsey fringeswith no microwave present. (b) Data showing modi-fied fringes when a phase varying microwave field of-pulse amplitude is introduced in zone M. (c) The-oretical plot corresponding to the data in (b) includingthe effect of velocity averaging.133aC)UCUl)LDC-1-Chapter 1. Quantum Optics and Photonicsd-1-1CAVITY COORDINATEFigure 4. Cavity cross-section in a TE102 resonator intwo different orientations. Plot I is the one usuallyused in microwave excitation, while Plot II is the oneused here.Chapter 1. Quantum Optics and Photonics,  I I 1 .. ..... 1 ..b -. ia. -? ---- -.... .. .. ......... ....... ...... .../ . w.......,, .... : . , .. .... , . i ....... ... detuningFigure 5. (a) Solid line shows the population changeas a function of the microwave detuning, the dip corre-sponding to zero detuning. Dashed line shows theusual Lorentzian lineshape seen when there is no phaseflip inside the cavity. (b) The experimental data corre-sponding to the solid line in (a).profile has a node,6 then this Lorentzianlineshape develops a dip that goes to zero onresonance. The unique property of this dip isthat it goes all the way to zero even forthermal beam with a wide velocity distribu-tion. This is different from the usual dip(inverse of figure 5a, dashed line) observedin microwave resonance, which, due tovelocity averaging, always remains wellabove zero. In addition, unlike the usual dip,this one remains zero at all powers. We canalso extend the theory behind this effect toseparated field excitations, suggesting thatlocking microwave oscillator to this lineshapemight result in reduced shot noise.We can more easily understand the physicalaspects of this effect in terms of Blochvectors.7  During the first half of theexcitation, the vector rotates through anangle (e.g., 7r/2 for a 7r/2 pulse) in the Rabiflop plane. Next, the vector rotates by anangle n in the phase plane, continuing torotate in the same direction in the Rabi flopplane. If the pulse strength in the two lobesis equal, the rotation in the first lobe isundone. The initial amount of rotation mustbe arbitrary for total cancellation to occur.Thus, cancellation would occur for any pulsestrength. In addition, this implies that dif-ferent atoms with different velocities wouldbe cancelled totally. The dip, therefore,would go to zero even for a thermal beamhaving a wide velocity distribution and inho-mogeneous transit time broadening.When the microwave is detuned, the vectorno longer rotates in the Rabi-flopping plane.This negates total cancellation and generatesmaximum population inversion when theamplitude of the detuning is of the order ofthe Rabi frequency. Thus the spectrum, as afunction of detuning, appears as two peaks;the separation between them increases as themicrowave power increases. Figure 5bshows a lineshape with an average micro-wave power corresponding to approximatelya it-pulse. Figure 5a, solid line, shows thecorresponding theoretical plot, with goodagreement. In comparison, the dashed line infigure 5a shows the corresponding lineshapefor a conventional configuration.By changing the level with an observablepopulation, the peak of figure 5a, dashedline, can be converted into a dip. Figure 6ashows a set of these dips (corresponding tocavity cross-section I) as the microwave Rabifrequency varies. The dip moves up anddown as microwave power changes, butnever moves close to zero. In contrast, figure6b shows the dips (corresponding to cavitycross-section II) as the microwave Rabi fre-quency varies by the same amounts as infigure 6a. The dip is always at zero, inde-pendent of changes in microwave power.Figure 6c also shows this, illustrating that thesignal at the bottom of the dip varies as afunction of Rabi frequency for these two setsof lineshapes.6 J.A. Kong, Electromagnetic Wave Theory. (New York: John Wiley, 1988).7 M. Sargent III, M.O. Scully, and W.E. Lamb, Jr., Laser Physics. (Reading, Massachusetts: Addison-Wesley, 1979).134 RLE Progress Report Number 132Chapter 1. Quantum Optics and Photonics. .... . ... ,........ . ... .. _ ....... ............ T -..... " ..... "..... .i** .. ........: • : : . : : .fh . : •. 'U.3.iN3otH..~* .. .4*~44 U1 I 1 * .DETUNING I(d)B ,.304.o 1.DETUNIN(b).............. ...... .... ..... .. ...... .... .... ....... .....:.. .. ....... ? ... ......1  . ...' .... ..... .... ~.. .. ........................... 0.4 ~ , ~ 1... ... .. ...... ........ ............/ .....W . . .... .. -...-.! . ... .........................____ I I ) ( ~ l ~*1.IRABI FREQUENCY(c)135.II1., ... ... . .... *.... ...... . *...... .... ....... *.......:,. . ) |..........--..... .. ..... ( Y- --... . ................Figure 6. (a) Conventional dips for cross-section I, as the Rabi frequency is varied. (b) Corresponding set for newdips seen in cross-section II. (c) How the dips in sets I and II move as the Rabi frequency is varied continuously.--- --- - - . l U1hL s *~Y a hlm e we swwwwwwwwn .. m..mm 6iPI ' ~I*-LM-L---.-~.~n ;: r -sI 1I I I IChapter 1. Quantum Optics and Photonics1.3 Stimulated BrillouinFiberoptic GyroscopeSponsorCharles S. Draper LaboratoryFiberoptic inertial rotation sensors (orgyroscopes) have been based on the Sagnaceffect in either a multiturn interferometer 8 ora resonator.9 Both of these approaches con-stitute the fiberoptic implementation of previ-ously demonstrated Sagnac interferometer' 0gyroscopes and resonator" gyroscopes thatemploy bulk-optic components. However,we have recently begun to study a fiberopticanalog of the ring laser gyroscope,12 whichwas a bulk-optic device. In the followingfigures, we are presenting preliminary dataon a fiberoptic ring laser gyroscope withstimulated Brillouinl3 scattering as the lasergain medium. To our knowledge, this is thefirst demonstration of a solid state ring lasergyroscope or RLG.Figure 7 is a simplified diagram of a stimu-lated Brillouin fiberoptic gyroscope. A singlefrequency laser, He-Ne at 1.15 ym, iscoupled into the opposite direction from anon-polarization maintaining fiberoptic ringresonator (length - 25m; finesse = 250; coildiameter % 7.5cm) and acts as the pump forthe stimulated Brillouin laser. The frequencyof the Brillouin laser14 is downshifted fromthat of the pump by the acoustic frequencyin the fiber (15 GHz at 1.15 Mm). The direc-tion of the Brillouin laser is opposite from thepump's because it experiences the highestBrillouin gain. The clockwise pump in theresonator is denoted by P- and the counter-clockwise pump by P . The correspondingstimulated Brillouin lasers that are created bythe pumps are denoted by B- and B+.To maintain the highest pump intensity in theresonator, the pump laser must be held at acavity resonance by using a feedback loop.The threshold pump intensity for Brillouinlasing depends on the length and finesse ofthe resonator, as well as on the wavelengthof the pump. In our case, we have achievedthreshold intensities as low as 60 MW at theinput of the resonator.The counterpropagating Brillouin lasers, B+and B-, coupled out of the resonator usingfiber coupler C1, are brought together onto adetector via coupler C2. In the presence ofinertial rotation, a beat note is generatedbetween B+ and B-, proportional to theapplied rotation component normal to theplane of the resonator, which is similar to theconventional R LG.Figure 8a shows the Brillouin beat frequency(converted to an analog signal) as a functionof a sinusoidal rotation (figure 8b) applied tothe table supporting the gyro. The peak beat8 V. Vali and L.W. Shorthill, "Fiber Ring Interferometer," Appl. Opt. 15, 1099 (1976).9 R.E. Meyer, S. Ezekiel, D.W. Stowe and V.J. Tekippe,Opt. Lett. 8:644 (1983)."Passive Fiber Optic Ring Resonator for Rotation Sensing,"10 W.R. Carrington, R. Fredricks, and Lear Siegler, Inc., Development of an Optical Sensor: Final Report to the U.S.Office of Naval Research on Contract N00014-73-C-0377, November 1973.11 S. Ezekiel and S.R. Balsamo, "Passive Ring Resonator Laser Gyroscope," App/. Phys. Lett. 30:478 (1977).12 A.H. Rosenthal, "Regenerative Circulatory Multiple-Beam Interferometry for the Study of Light-PropagationEffects," J. Opt. Soc. Am. 52:1143 (1962); W.M. Macek and D.T.M. Davis, Jr., "Rotation Rate Sensing with Trav-eling Wave Ring Laser," Appl. Phys. Lett. 2:67 (1963).13 P.J. Thomas, H.M. van Driel, and G.I.A. Stegeman, "Possibility of Using an Optical Fiber Brillouin Ring Laser forInertial Sensing," Appl. Opt. 19:1906 (1980).14 K.O. Hill, B.S. Kawasaki, and D.C. Johnson, "Cw Brillouin Laser," Appl. Phys. Lett. 28:608 (1976); D.R. Ponikvarand S. Ezekiel, "Stabilized Single-Frequency Stimulated Brillouin Fiber Ring Laser," Opt. Lett. 6:398 (1981); L.F.Stokes, M. Chodorow, and H.J. Shaw, "All Fiber Stimulated Brillouin Ring Laser with Submilliwatt Pump Thres-hold," Opt. Lett. 7:509 (1982); P. Bayvel and I.P. Giles, "Evaluation of Performance Parameters of Single Mode AllFiber Brillouin Ring Lasers," Opt. Lett. 14:581 (1989).136 RLE Progress Report Number 132Chapter 1. Quantum Optics and PhotonicsFigure 7.frequency is about 3 kHz which is close tothe 3.2 kHz value we calculated using themaximum applied rate of 3.8 deg/sec and thescale factor for the gyro. Figure 8a showsthat a zero beat frequency appears wheneverthe rotation rate is low. This dead zone isthe familiar "lock-in" phenomenon in RLGsthat is caused by backscattering. The lock-inrange is about 1 kHz or 1 deg/sec. Figure 7shows that the beat frequency does notchange sign with the rotation because thesetup cannot detect the beat frequencyphase.E- p-(a) 3 kHzT(b)Figure 8.137In the bulk-optic RLG, use of mechanicaldither overcomes the lock-in effect. In thecase of the Brillouin RLG or B-RLG, we canalso use mechanical dither to overcomelock-in. Other techniques, similar to thosebased on multiple frequency operation, canbe implemented in the B-RLG, but not in theRLG.Because the B-RLG does not require a meas-urement system for detecting the Sagnaceffect, it has a major advantage over interfer-ometers, which need to measure the Sagnacphase shift, and resonators that mustmeasure frequency shift. In the B-RLG,similar to the RLG, the output is a beat fre-quency directly proportional to rotation rate.We must study the preliminary data toresolve a number of issues that influence ulti-mate performance. At present, the B-RLG,which is basically simpler to implement anddoes not require highly specialized compo-nents, is a promising alternative to passivefiber interferometer and fiber resonator gyros.Professor Daniel Kleppner, Associate Director, Research Laboratory of Electronics138 RLE Progress Report Number 132