2900- 104- R Memorandum of Project MICHIGAN OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW TEMPERATURES JOHN LAMBE JOHN BAKER November 1959 SOLID-STATE PHYSICS LABORATORY THE U N I V E R S I T Y OF M I C H I G A N Ann Arbor, Michigan

DISTRIBUTION OF REPORTS Distribution control of Project MICHIGAN Reports has been delegated by the U. S. Army Signal Corps to: Commanding Officer U. S. Army Liaison Group Project MICHIGAN Willow Run Laboratories Ypsilanti, Michigan It is requested that information or inquiry concerning distribution of reports be addressed accordingly. Project MICHIGAN is carried on for the U. S. Army Signal Corps under Department of the Army Prime Contract Number DA-36-039 SC- 78801. University contract administration is provided to the Willow Run Laboratories through The University of Michigan Research Institute.

WILLOW RUN LABORATORI ES TECH N ICAL MEMORANDUM 2900-104-R PREFACE Documents issued in this series of Technical Memorandums are published by Willow Run Laboratories in order to disseminate scientific and engineering information as speedily and as widely as possible. The work reported may be incomplete, but it is considered to be useful, interesting, or suggestive enough to warrant this early publication. Any conclusions are tentative, of course. Also included in this series will be reports of work in progress which will later be combined with other materials to form a more comprehensive contribution in the field. A primary reason for publishing any paper in this series is to invite technical and professional comments and suggestions. All correspondence should be addressed to the Technical Director of Project MICHIGAN. Project MICHIGAN, which engages in research and development for the U. S. Army Combat Surveillance Agency of the U. S. Army Signal Corps, is carried on by the Willow Run Laboratories as part of The University of Michigan' s service to various government agencies and to industrial organizations. Robert L. Hess Technical Director Project MICHIGAN 111

WILLOW RUN LABORATORI ES TECHNICAL MEMORANDUM 2900-104-R ABSTRACT Because of possible maser applications, the interaction of light with spin systems has been of considerable interest. In this connection, experiments have been carried out to study the effect of light on the spin resonance of F-centers. These experiments were done at liquid-helium temperatures because, at this temperature, the F-center has a long spin-lattice relaxation time. It was found that the spin population could be significantly affected by optical illumination. It is possible that such an effect could be useful in pumping a three-level maser system from an optically "heated" two-level spin system. INTRODUCTION The subject of the interaction of light with spin systems has been of considerable interest because of possible maser applications. Effects which come under the general heading of "optical pumping" may permit the use of light sources as the pump in maser systems. Although such effects have been extensively studied in gases, the work in solids is much less extensive. This memorandum contains a discussion of measurements made on a system consisting of F-centers in KC1. Such centers have well established spin-resonance and optical properties. Of special interest is that the F-center has very strong optical absorption and a long spinlattice relaxation time at 40K. A value of 15 sec has been reported (Ref. 1). Basically, the objective is to alter the spin temperature of the F-centers by irradiation with F-band light. This is a crude but simple way to see whether optical pumping will occur. It should be noted that the optical excited states are very broad in energy, thereby making the more elegant type of experiments, such as are carried out in sodium vapor, unfeasible. Thus it is doubtful that one could optically invert the spin population in the F-center case.'A speech presenting the material of this memorandum was presented at the International Conference on Quantum Mechanics, High View, New York, 14-16 September 1959.

WI LLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-104-R The question of the nature of the excited electronic states of the F-center is of fundamental importance in determining whether spin-flips can occur in the optical excitation process. This is dependent on the mixing of spin states in the excited state. The usual procedure has been to consider the first excited state as a p state, and on this basis calculations of the energy of this state have been made. No calculations appear to have been made on the spin-orbit coupling in the excited state. For these purposes a situation analogous to an alkali-metal atom with broadened energy levels is assumed. On this basis, significant spin-optical interaction would exist. In addition to the occurrence of spin-flipping during optical transitions, there is the problem of what happens to the spin of the F-center due to the local "heating" of the F-center; that is, the F-center absorbs 2. 5 ev of energy and emits about 1 ev as light (Ref. 2). The rest of the energy is coupled to the lattice surrounding the F-center. The surrounding atoms vibrate quite strongly, and the F-center finally cools off. This process may increase the temperature of the spin system. Since little is known about such a process, the present type of measurement may aid in understanding such effects. 2 EXPERIMENTAL METHOD The apparatus used consisted of a magnetic resonance spectrometer operating at about 9400 me and an arc light source with appropriate filters to select a band of radiation in the F-center wavelength region. The microwave cavity had the dimensions of standard X-band waveguide and was operated in the TE012 mode. The cavity was made of a ceramic type of material which was silver coated. A window was cut in the broad face of the cavity to permit illumination of the sample (Fig. 1). It was necessary to use superheterodyne detection, since small microwave power was used to minimize saturation problems. The power level used was between 0. 05 and 0. 005 uw. Although this was still somewhat excessive, reasonable data could be obtained under these conditions. Crystals used were of commercially available KC1, which were cleaved to about 3-mm thickness and 1 cm on a side. These crystals were x-rayed for about an hour to produce a peak F-band optical density of about 1. 2 at room temperature. The crystals were kept in the dark or in red light until immersion in liquid helium. This was necessary in order to avoid growth of M- and R-bands which are known to effect the F-center luminescence. 2

WILLOW RUN LABORATORI ES TECH N ICAL MEMORANDUM 2900-104-R Sample Holder Magnet Dewars FIG. 1. APPARATUS USED FOR OPTICAL SPIN RESONANCE EXPERIMENT. Cavity and sample are immersed in liquid helium. Dewar system is slit silvered to permit sample illumination. The cavity is shown with the connecting waveguide. The crystals were then put into the cavity, which was in the liquid-helium dewar, so that the crystals were completely immersed in liquid helium. The spin resonance signal was then observed with light on and off the crystal. A Zr arc used together with the optical system gave an illumination intensity of about 1 mw/cm at the crystal. The light had to pass through the dewar system (the dewars were slit silvered) and onto the crystal. EXPERIMENTAL RESULTS The first runs were made simply to observe the spin resonance of the F-center. At this point it was noted that numerous other spin-resonance signals were present from the sample. A typical spectrum is shown in Fig. 2. The F-center resonance is distorted due to saturation effects. The other lines are present in the KC1 even before x-raying. These signals were 3

WI LLOW RUN LABORATORI ES TECHNICAL MEMORANDUM 2900-104-R found in commercially available KC1 from 3 different sources. The origin of this spectra remains unknown, but these lines serve the useful purpose of a lattice thermometer for the experiment. The unknown center has a spin-lattice relaxation time which is much shorter than the F-center so it can function as a thermometer for the lattice. F- center 880 Gauss FIG. 2. TYPICAL KC1 SPECTRA AT 4. 20K. The F-center absorption is distorted. The other narrow line spectra is angular dependent. The effect of light on the crystal is shown in Fig. 3. Here the microwave bridge was adjusted to observe dispersion signals. The F-center signal was distorted, but was still useful as a population measurement. It was observed that the F-center resonance signal decreased by about 50%. The "thermometer signal" remained essentially unaffected. From this it was concluded that the spin population of the F-center system had been altered. The effect was equivalent to a 4~K increase in temperature. 4

WI LLOW RUN LABORATORI ES TEC H N ICAL MEMORANDUM 2900-104-R Off FIG. 3. DISPERSION SIGNAL OBTAINED WITH LIGHT ON AND LIGHT OFF. The signal to the high-field side of the F-center is used as a thermometer. After the light was turned off, the F-center resonance returned to its original form. About 1 min was required to remove all trace of the light effect. On the basis of the long spinlattice relaxation time of the F-center, this was to be expected. 4 DISCUSSION As reported in the foregoing sections, an effect on the F-center spin-resonance signal was observed. It is of interest to discover what a crude calculation would predict as to the expected magnitude of the effect.

WILLOW RUN LABORATORIES TECHN ICAL MEMORANDUM 2900-104-R The system under discussion contains about 1016 F-centers, and was absorbing 1 mw of 15 green light. This means about 2 x 10 quanta per second are absorbed. The situation can be analyzed as follows. Let n1 = number of spins in lower state n2 = number of spins in upper state F = rate of spin flipping by light per center. dn Then = -Fn + Fn2 - w12nl + 21 n2' dn2 and = -Fn2 + Fnl + 12nl - 21n2 Let An = n - n T = spin-lattice relaxation time (15 sec). This yields dAn 1 dt -2FAn - (An - An). dt 0? An estimate of F is given by 2 x 10 photons/second 1 F =X 1016 centers The factor of 1/2 is a statement of the assumption that the optically excited center has equal probability of going back to either spin state. Then dAn 1 An - 15n - An dt 5 15 0 at equilibrium dAn/dt = 0, so that 1 An = - An. Thus the observed effect is of the proper order of magnitude. However, the data is not good enough to provide a severe test of the assumed model.

WI LLOW RUN LABORATORI ES TEC H N ICAL MEMORANDUM 2900-104-R The local heating effect may also be contributing to the observed spin temperature effect. An interesting experiment would be to see if the nuclear spin temperature is affected by the fact that nuclei are set in rapid motion in the neighborhood of the paramagnetic center. In this way more information might be obtained on local heating around the F-center. It should be pointed out that there is little hope of optically inverting the F-center spin system. Yet the fact that a spin system can be heated optically has an important implication for optical pumping in solids. A very interesting system could be achieved by placing such a heated spin system in contact with a three-level maser system. By matching levels 1 and 3 to the hot two-level system, cross relaxation effects could tend to saturate between levels 1 and 3. Maser action could then be achieved between levels 2 and 3. This would be of special interest in cases where the separation between 1 and 3 is very large, since in this case, optical "spin heating" becomes more feasible. Thus optical "spin heating" may be used where the usual optical pumping inversion techniques are not applicable. REFERENCES 1. Noble, G. A., "F-Center Relaxation Times at 40K, " Bull. Am. Phys. Soc., 1959, Vol. 4, p. 326. 2. Botden, van Doom, and Haven, Luminescence of Color Centers Eindhoven, Netherlands, Philips Research Laboratories, 1954, Report No. 9, p. 469.

WILLOW RU N LABORATORI ES TECH N ICAL MEMORANDUM 2900-104-R DISTRIBUTION LIST 6, PROJECT MICHIGAN REPORTS 1 November 1959 - Effective Date Copies - Addressee Copies - Addressee 1 Office, Chief of Research and Development 4 Director Department of the Army U. S. Army Engineer Research and Development Laboratories Washington 25, D. C. Fort Belvoir, Virginia ATTN: Army Research Office (1) ATTN: Chief, Topographic Engineer Department (2) ATTN: Chief, Electrical Engineering Department 1 Office, Assistant Chief of Staff for Intelligence (1) ATTN: Technical Documents Center Department of the Army Washington 25, D. C. 1 Commanding General U. S. Army Combat Development Experimentation Center ATTN: Chief, Combat Developments/G-2 Air Branch Fort Ord, California 1 Commanding General 1 Commandant U. S. Continental Army Command U. S. Army Command and General Staff College Fort Monroe, Virginia Fort Leavenworth, Kansas ATTN: ATSWD-G ATTN: Archives 2 Commanding General 2 Assistant Commandant U. S. Army Combat Surveillance Agency U. S. Army Artillery and Missile School 1124 N. Highland Street Fort Sill, Oklahoma Arlington 1, Virginia 3 Assistant Commandant, U. S. Army Air Defense School 1 Chief, Research and Development Division Fort Bliss Texas Office of the Chief Signal Officer Department of the Army 1 Commandant, U. S. Army Engineer School Washington 25, D. C. Fort Belvoir, Virginia 25 Commanding Officer ATTN: Combat Developments Group U. S. Army Signal Research and Development Laboratory Fort Monmouth, New Jersey 1 Commandant, U. S. Army Signal School Fort Monmouth, New Jersey ATTN: SIGFMI/EL-DR ATTN: SIGFM/SC-DO 1 Commanding General U. S. Army Electronic Proving Ground 1 Commandant, U. S. Army Aviation School Fort Huachuca, Arizona Fort Rucker, Alabama ATTN: Technical Library 3 President, U. S. Army Artillery Board Fort Sill, Oklahoma 1 Office of the Director, Defense Research and Engineering Technical Library 1 President, U. S. Army Air Defense Board Department of Defense Fort Bliss, Texas Washington 25, D. C. 1 President i Chief of Engineers Department of the Army U. S. Army Airborne and Electronics Board Department of the Army Fort Bragg, North Carolina Washington 25, D. C. ATTN: Research and Development Division 1 Commanding Officer U. S. Army Signal Electronic Research Unit 1 Office, Chief of Ordnance Post Office Box 205, Mountain View, California Research and Development Division Department of the Army 1 Chief of Naval Operations (OP-37) Washington 25, D. C. Department of the Navy Washington 25, D. C. ATTN: ORDTB, Research and Special Projects 1 Office of the Chief of Naval Operations, Op-07T 1 Commanding General Building T-3, Department of the Navy Quartermaster Research and Engineering Command Washington 25, D. C. U. S. Army Natick, Massachusetts 3 Office of Naval Research (Code 463) Department of the Navy 2 Chief, U. S. Army Security Agency 17th and Constitution Avenue, N. W. Arlington Hall Station Washington 25, D. C. Arlington 12, Virginia 1 Chief, Bureau of Ships 2 Commander, Army Rocket and Guided Missile Agency Department of the Navy Redstone Arsenal, Alabama Washington 25, D. C. ATTN: Technical Library, ORDXR-OTL ATTN: Code 690 8

WILLOW RUN LABORATORI ES TECHN ICAL MEMORANDUM 2900-104-R DISTRIBUTION LIST 6 1 November 1959 - Effective Date Copies - Addressee Copies - Addressee 2 Director, U. S. Naval Research Laboratory 5 National Aeronautics and Space Administration Washington 25, D. C. 1520 H. Street, Northwest Washington 25, D. C. ATTN: Code 2027 2 Combat Surveillance Project 1 Commanding Officer, U. S. Navy Ordnance Laboratory Corne Aeronautica Laboratory, Inc. Cornell Aeronautical Laboratory, Inc. Corona, California Box 168, Arlington 10, Virginia ATTN: Library ATTN: Technical Library 1 Commanding Officer and Director 1 The RAND Corporation U. S. Navy Electronics Laboratory 1700 Main Street, Santa Monica, California San Diego 52, California ATTN: Library ATTN: Library 1 Chief Scientist, Research and Development Division 4 Department of the Air Force, Headquarters, USAF Office of the Chief Signal Officer Washington 25, D. C. Department of the Army (1) ATTN: AFOIN-1B1 Washington 25, D. C. (1) ATTN: AFOAC -E/A (1) ATTN: AFOAC-E/A 1 Stanford Research Institute, Document Center (1) ATTN: AFDRD (1) ATTN: AFDRD Menlo Park, California (1) ATTN: Directorate of Requirements ATTN: Acquisitions 3 Commander in Chief Headquarters, Strategic Air Command 1 Operations Research Office Offutt Air Force Base, Nebraska The Johns Hopkins University (1) ATTN: DINC 6935 Arlington Road (21) ATTN:w DIORP Bethesda, Maryland Washington 14, D. C. 3 Headquarters, Tactical Air Command ATTN: Chief Intelligence Division Langley Air Force Base, Virginia (1) ATTN: TOOA 1 Columbia University, Electronics Research Laboratories (2) ATTN: TORQ 632 W. 125th Street, New York 27, New York ATTN: Technical Library 1 Commander, Air Technical Intelligence Center Wright-Patterson Air Force Base, Ohio THRU: Commander, Rome Air Development Center Griffiss Air Force Base, New York ATTN: AFCIN-4B/a ATTN: RCSSTL-1 10 ASTIA (TIPCR) Arlington Hall Station 2 Cornell Aeronautical Laboratory, Inc. Arlington 12, Virginia 4455 Genesee Street, Buffalo 21, New York ATTN: Librarian 10 Commander, Wright Air Development Center Wright-Patterson Air Force Base, Ohio THRU: Bureau of Aeronautics Representative 4455 Genesee Street, Buffalo 21, New York (9) ATTN: WCLROR (1) ATTN: WCOSI-Library 1 Control Systems Laboratory University of Illinois, Urbana, Illinois 2 Commander, Rome Air Development Center Griffiss Air Force Base, New York ATTN: Librarian ATTN: RCVSL-1 THRU: ONR Resident Representative ATTN: RCWIR 1209 W. Illinois Street, Urbana, Illinois 1 Director, Air University Library 1 Polytechnic Institute of Brooklyn Maxwell Air Force Base, Alabama 55 Johnson Street, Brooklyn 1, New York ATTN: AUL-7971 ATTN: Microwave Research Institute Library 1 Commandant of the Marine Corps 1 The U. S. Army Aviation HRU Headquarters, U. S. Marine Corps P. O. Box 428, Fort Rucker, Alabama Washington 25, D. C. 1 U. S. Continental Army Command Liaison Officer Project MICHIGAN, Willow Run Laboratories 4 Ypsilanti, Michigan 4 Central Intelligence Agency 2430 E. Street, N. W. n2430 E Street, N. W. 1 Commanding Officer, U. S. Army Liaison Group Project MICHIGAN, Willow Run Laboratories ATTN: OCR Mail Room Ypsilanti, Michigan 9

+q+ + UNCLASSIFIED UNCLASSIFIED AD Div. 25/4 | 1. Light - Physical effects AD Div. 25/4 1. Light - Physical effects Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance -Spin Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance-Spin OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN TEMPERATURE by John Lambe and John Baker. Memorandum' II. Lambe, John, and TEMPERATURE by John Lambe and John Baker. Memorandum II. Lambe, John, and of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John ( Memorandum no. 2900-104-R) III. U. S. Army Signal Corps ( Memorandum no. 2900-104-R) III. U.S. Army Signal Corps (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36-039 SC-78801 ~~~~~~~~~~~~~~~~~~~~~~SC-78801 Because of possible maser applications, the interaction of light SC-78801 Because of possible maser applications, the interaction of light SC with spin systems has been of considerable interest. In this con- with spin systems has been of considerable interest. In this connection, experiments have been carried out to study the effect of nection, experiments have been carried out to study the effect of light on the spin resonance of F-centers. These experiments light on the spin resonance of F-centers. These experiments were done at liquid-helium temperatures because, at this tem- were done at liquid-helium temperatures because, at this temperature, the F-center has a long spin- lattice relaxation time. perature, the F-center has a long spin- lattice relaxation time. It was found that the spin population could be significantly affect- It was found that the spin population could be significantly affected by optical illumination. It is possible that such an effect could ed by optical illumination. It is possible that such an effect could be useful in pumping a three-level maser system from an optical- Armed Services be useful in pumping a three-level maser system from an optical- Armed Services ly "heated" two-level spin system. Technical Information Agency ly "heated" two-level spin system. Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED +~~~~~~ + UNCLASSIFIED UNCLASSIFIED AD Div. 25/4 | 1. Light - Physical effects AD Div. 25/4 1. Light - Physical effects Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance -Spin Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance-Spin OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN TEMPERATURE by John Lambe and John Baker. Memorandum II. Lambe, John, and TEMPERATURE by John Lambe and John Baker. Memorandum II. Lambe, John, and of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John ( Memorandum no. 2900-104-R) III. U. S. Army Signal Corps ( Memorandum no. 2900-104-R) III. U. S. Army Signal Corps (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36-039 ~~~~~~~~~~~~~~~~~~~~~~~~~~SC-7881 S-801 Because of possible maser applications, the interaction of light SC-78801 Because of possible maser applications, the interaction of light SC with spin systems has been of considerable interest. In this con- with spin systems has been of considerable interest. In this connection, experiments have been carried out to study the effect of nection, experiments have been carried out to study the effect of light on the spin resonance of F-centers. These experiments light on the spin resonance of F-centers. These experiments were done at liquid-helium temperatures because, at this tem- were done at liquid-helium temperatures because, at this temperature, the F-center has a long spin- lattice relaxation time. perature, the F-center has a long spin- lattice relaxation time. It was found that the spin population could be significantly affect- It was found that the spin population could be significantly affected by optical illumination. It is possible that such an effect could ed by optical illumination. It is possible that such an effect could be useful in pumping a three-level maser system from an optical- Armed Services be useful in pumping a three-level maser system from an optical- Armed Services ly "heated" two-level spin system. Technical Information Agency ly "heated" two-level spin system. Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED + ~ ~

AD UNCLASSIFIED AD UNCLASSIFIED UNITERMS UNITERMS Maser Maser Light Light Spin systems Spin systems Spin resonance Spin resonance F -centers F -centers Liquid helium Liquid helium Relaxation time Relaxation time Optical Optical Pumping Pumping UNCLASSIFIED UNCLASSIFIED AD UNCLASSIFIED AD UNCLASSIFIED UNITERMS UNITERMS Maser Maser Light Light Spin systems Spin systems Spin resonance Spin resonance F -centers F-centers Liquid helium Liquid helium Relaxation time Relaxation time Optical Optical Pumping UNCLASSIFIED UNCLASSIFIED

UNCLASSIFIED UNCLASSIFIED AD Div. 25/4 1. Light - Physical effects AD Div. 25/4 1. Light - Physical effects Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance - Spin Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance -Spin OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN TEMPERATURE by John Lambe and John Baker. Memorandum II. Lambe, John, and TEMPERATURE by John Lambe and John Baker. Memorandum II. Lamhe, John, and of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John (Memorandum no. 2900-104-R) III. U. S. Army Signal Corps ( Memorandum no. 2900-104-R) III. U. Signal Corps (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36-031 SC-78801 SC-78801 Because of possible maser applications, the interaction of light Because of possible maser applications, the interaction of light with spin systems has been of considerable interest. In this con- with spin systems has been of considerable interest. In this connection, experiments have been carried out to study the effect of nection, experiments have been carried out to study the effect of light on the spin resonance of F-centers. These experiments light on the spin resonance of F-centers. These experiments were done at liquid-helium temperatures because, at this tem- were done at liquid-helium temperatures because, at this temperature, the F-center has a long spin- lattice relaxation time. perature, the F-center has a long spin- lattice relaxation time. It was found that the spin population could be significantly affect- It was found that the spin population could be significantly affected by optical illumination. It is possible that such an effect could ed by optical illumination. It is possible that such an effect could be useful in pumping a three-level maser system from an optical- Armed Services be useful in pumping a three-level maser system from an optical- Armed Services ly "heated" two-level spin system. Technical Information Agency ly "heated" two-level spin system. Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED AD Div. 25/4 1. Light - Physical effects AD Div. 25/4 1. Light - Physical effects Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance -- Spin Willow Run Laboratories, U. of Michigan, Ann Arbor 2. Resonance-Spin OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN OPTICAL EFFECTS ON F-CENTER SPIN RESONANCE AT LOW I. Project MICHIGAN TEMPERATURE by John Lambe and John Baker. Memorandum II. Lambe, John, and TEMPERATURE by John Lambe and John Baker. Memorandum II. Lamhe, John, and of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John of Project MICHIGAN. Nov 59. 7 p. incl. illus., 2 refs. Baker, John ( Memorandum no. 2900-104-R) III. U. S. Army Signal Corps ( Memorandum no. 2900-104-R) III. U. Signal Corps (Contract DA-36-039 SC-78101) Unclassified memorandum IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum IV. Contract DA-36 -031 S~~~~~~~~~~~~~~~~~~~~~~~~~~C-78811S-8 01 Because of possible maser applications, the interaction of light SC-78801 Because of possible maser applications, the interaction of light with spin systems has been of considerable interest. In this con- with spin systems has been of considerable interest. In this connection, experiments have been carried out to study the effect of nection, experiments have been carried out to study the effect of light on the spin resonance of F-centers. These experiments light on the spin resonance of F-centers. These experiments were done at liquid-helium temperatures because, at this tern- were done at liquid-helium temperatures because, at this temperature, the F-center has a long spin- lattice relaxation time. perature, the F-center has a long spin- lattice relaxation time. It was found that the spin population could be significantly affect- It was found that the spin population could be significantly affected by optical illumination. It is possible that such an effect could ed by optical illumination. It is possible that such an effect could be useful in pumping a three-level maser system from an optical- Armed Services be useful in pumping a three-level maser system from an optical- Armed Services ly "heated" two-level spin system. Technical Information Agency ly "heated" two-level spin system. Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED +4 +q~

AD UNCLASSIFIED AD UNCLASSIFIED UNITERMSUNITERMS Maser Maser Light Light Spin systems Spin systems Spin resonance Spin resonance F-centers F-centers Liquid helium Liquid helium Relaxation time Relaxation time Optical Optical Pumping Pumping UNCLASSIFIEDUNCLASSIFIED — 3 CA__ -~ z 01__ AD UNCLASSIFIED AD UNCLASSIFIED UNITERMSUNITERMS Maser Maser Light Light Spin systems Spin systems Spin resonance Spin resonance F-centers F-centers Liquid helium Liquid helium Relaxation time Relaxation time Optical Optical Pumping Pumping UNCLASSIFIEDUNCLASSIFIED