Laser Magnetometry Using DBR Laser Pumped Helium Isotopes: Beyond

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Laser Magnetometry Using DBR Laser Pumped Helium
IsotopesBeyond Juno at Jupiter (LEOS April
24, 2008)  Robert E. Slocum, PhDChief
Technical OfficerPolatomic, Inc.1810 Glenville
DriveRichardson, TX 75080(972) 690-0099
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Geophysical Service Inc./Texas Instruments Circled
are Cecil H. Green (L) and Robert E. Slocum (R)
Sputnik October 1957
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Vector Helium 4 Magnetometer (VHM) sensor
concept.
Mariner 4 launch for Mars 11/28/64
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Vector Mode OperationVariable Density Optical
Filter

• Metastable helium subjected to circular
  polarized radiation and rotating magnetic sweep
  field BS.
• Optical pumping efficiency and absorption
  depends on angle between field and optical axis.
• Signal ? cos2 ?, minimum signal and maximum
  absorption at ? ?/2.

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Vector ImplementationBias Nulling Field Mode

• Signal ? cos2 ?.
• External ambient field B0 causes phase shift of
  signal.
• Feedback steady field BF to null ambient field
  and cause maximum absorption to occur at ??/2.
• Feedback currents IF are a measure of the
  ambient field components.

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NOBLE PRIZE RESEARCH CONTRIBUTING TO TECHNOLOGY
OF LASER MAGNETIC FIELD SENSORS

• 2000 ZHORES I. ALFEROV, and HERBERT KROEMER for
  developing semiconductor heterostructures used in
  high-speed- and opto-electronics and JACK ST.
  CLAIR KILBY for his part in the invention of the
  integrated circuit.
• 1997 CLAUDE COHEN-TANNOUDJI for development of
  methods to cool and trap atoms with laser light.
• 1989 NORMAN F. RAMSEY for the invention of the
  separated oscillatory fields method and its use
  in the hydrogen maser and other atomic clocks.
  HANS G. DEHMELT and WOLFGANG PAUL for the
  development of the ion trap technique.
• 1981 NICOLAAS BLOEMBERGEN and ARTHUR L. SCHAWLOW
  for their contribution to the development of
  laser spectroscopy.
• 1966 ALFRED KASTLER for the discovery and
  development of optical methods for studying
  hertzian resonances in atoms.
• 1964 CHARLES H. TOWNES, NICOLAY GENNADIYEVICH
  BASOV and ALEKSANDR MIKHAILOVICH PROKHOROV for
  fundamental work in the field of quantum
  electronics, which has led to the construction of
  oscillators and amplifiers based on the
  maser-laser principle.
• 1956 WILLIAM SHOCKLEY, JOHN BARDEEN and WALTER
  HOUSER BRATTAIN for their researches on
  semiconductors and their discovery of the
  transistor effect.
• 1955 POLYKARP KUSCH for his precision
  determination of the magnetic moment of the
  electron.
• 1952 FELIX BLOCH and EDWARD MILLS PURCELL for
  their development of new methods for nuclear
  magnetic precision measurements and discoveries
  in connection therewith.
• 1944 ISIDOR ISAAC RABI for his resonance method
  for recording the magnetic properties of atomic
  nuclei.
• 1943 OTTO STERN for his contribution to the
  development of the molecular ray method and his
  discovery of the magnetic moment of the proton.
• 1933 ERWIN SCHRÖDINGER and PAUL ADRIEN MAURICE
  DIRAC for the discovery of new productive forms
  of atomic theory.
• 1932 WERNER HEISENBERG for the creation of
  quantum mechanics, the application of which has,
  inter alia, led to the discovery of the
  allotropic forms of hydrogen.
• 1922 NIELS BOHR for his services in the
  investigation of the structure of atoms and of
  the radiation emanating from them.
• 1918 MAX KARL ERNST LUDWIG PLANCK in recognition
  of the services he rendered to the advancement of
  Physics by his discovery of energy quanta.
• 1902 HENDRIK ANTOON LORENTZ and PIETER ZEEMAN in
  recognition of the extraordinary service they
  rendered by their researches into the influence
  of magnetism upon radiation phenomena.

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Fig. 1 Energy level diagram for helium 4.
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He4 Cell Sensing ElementVariable Density
Optical Filter Magnetically Controlled

• Glass cell contains He4 at low pressure (1.5
  Torr).
• HF discharge produces metastable 23S1 ground
  state.
• External ambient field B0 splits energy into
  three Zeeman levels m1,0,-1.
• Separation energy ?E h?0 where ?0 (?e / 2?)
  B0 and ?e / 2? 28.0249540 Hz/nT
• Metastables in 23S1 level are atomic magnets.

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Optical Pumping

• Pumping produces non-equilibrium distribution of
  atoms among different energy levels.
• m1,0,-1 sublevels are equally populated in
  thermal equilibrium.
• m-1 has high absorption probability for
  circular polarized 1083 nm laser radiation.
• 23P0 atoms decay to m sublevels at equal rates.
• Laser pumping produces magnetic moment M
  opposite field as atoms shift to m0,1.

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Scalar Mode OperationMagnetically-Driven Spin
Precession (MSP)

• Metastable helium subjected to circular
  polarized radiation and RF magnetic field BRF .
• Absorption increases when RF magnetic field is
  at resonance (Larmor frequency) ?0 .
• RF resonant radiation causes transitions between
  magnetic sublevels (?E h?0 ).
• Separation energy ?E h?0 where ?0 (?e / 2?)
  B0 and ?e / 2? 28.0249540 Hz/nT.
• B0 1.42 x 106 Hz / 28.0249540 Hz/nT 50,669
  nT.

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Scalar Mode ImplementationMagnetically-Driven
Spin Precession (MSP)

• Apply periodic sweep to RF oscillator.
• Causes periodic modulation of detector output.
• Phase synchronous demodulation determines ?0 .

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OSP BLOCH EQUATIONS

• The OSP effect can be described using the
  modified Bloch equations for description of the
  behavior of the bulk magnetization M in an
  optically pumped medium as it experiences
  magnetic resonance. The time dependent
  magnetization M0(t)/? is given by M0(t) A
  B?cos ?t,
•  
• where the OSP magnetic resonance drive frequency
  is ? 2?? (? is the actual Larmor frequency for
  the helium sample). The optically detected light
  beam intensity is given by
•  
• Is(t) KM0(t)?M?(t),
•  
• where K is a proportionality constant and M?(t)
  is the magnetization along the optical axis. The
  Bloch equations can be solved for the case where
  the beam has 100 modulation (A 0) to obtain
  the following expression for Is(t)
• Is(t) 1/4KB2?sin2 ? / 1 (? - ?0)2?2
• 1/4 KB2?sin2 ? cos 2?t / 1 (? -
  ?0)2?2
• (? - ?0)? ?sin 2?t / 1 (? - ?0)2?2.
•  

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Scalar Mode OperationOptically-Driven Spin
Precession (OSP)

• Metastable helium subjected to pulsed circular
  polarized radiation.
• Optical pumping efficiency increases at Larmor
  frequency ?0 .
• ?0 (?e / 2?) B0 and ?e / 2? 28.0249540
  Hz/nT.
• B0 1.42 x 106 Hz / 28.0249540 Hz/nT 50,669
  nT.

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Scalar Mode ImplementationOptically-Driven Spin
Precession (OSP)
?0

• Apply periodic sweep to RF oscillator.
• Causes periodic modulation of detector output.
• Phase synchronous demodulation determines ?0 .

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Comparison of OSP and MSP magnetic resonance
signals for identical laser pump source and
helium cells.
OSP RESONANCE
MSP RESONANCE
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An oblique view of the Juno spacecraft shows the
three solar panels, one of which carries the
magnetometer (yellow extension on the upper solar
panel in this image). The main body of the
spacecraft is underneath the high gain antenna,
which is used for communications to Earth. The
three solar panels are built in four-hinged
sections that allow the spacecraft to fit within
the rocket for launch.
The Juno spacecraft in front of Jupiter. Juno is
one of the largest planetary spacecraft to ever
be launched.
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Omni-directional laser-pumped sensor and
lamp-pumped sensor.
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Self-Calibrating Vector Helium Magnetometer
Photodiode B
He-4 cell
Photodiode A
Optical Isolator
PM Fiber
He-4 cell
Laser
Intensity Modulator
?/2
Collimating Lens
?/4
Tri-Axial Coils
Polarizing Beamsplitter Cubes

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Technical Objectives for Self-Calibrating Vector
Helium Magnetometer

• Vector field measurement
• Self-calibrated by scalar measurement
• Calibrated range of (1,000 nT to 65,000 nT)
• Omni-directional sensitivity
• Fiber-coupled laser
• Bias Field Nulling (BFN) technique for vector
  measurements
• Optical Spin Precession (OSP) for scalar
  measurements
• Reduced sensor volume and mass
• Calibrated vector accuracy of 1 nT
• Sensitivity of 5 pT/vHz

SENSOR UNIT
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MVLM Calibration Process

• Calibration Requirements
• Nine coefficients required to calibrate vector
  magnetometer.
• Three offsets in absence of magnetic field.
• Three scale factors (gains) for normalization of
  axes.
• Three non-orthogonality angles which build up
  orthogonal system in sensor.
• Year 3/NCE Algorithm Implementation Completed
• Vector mode measurements made using BFN
  technique (goal 0.1 accuracy).
• Scalar mode measurements made using OSP and MSP
  technique (goal 0.001 accuracy).
• Multiplex vector and scalar measurements for
  different sensor orientations.
• Acquire data and calculated calibration
  coefficients.
• Developed calibration algorithm evolved from
  compensation algorithm used for Navy airborne
  systems.
• NASA/ESA Standard for Calibration
• Use of MSP or OSP provides omni-directional
  pre-flight scalar field values used for vector
  calibration using single MVLM cell. This method
  can be validated in future calibration
  experiments at the GSFC coil facility.

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15 August, 2005 Learning Data Set
RMSE before 28.80867
RMSE after 0.82896
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POLATOMIC 2000 SINGLE AXIS GRADIOMETER ON 25 cm
SPACING
MAD
MCM
Noise characteristics the POLATOMIC 2000 based
on 45 minute data collection period.
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Underwater Magnetic and Electric Fields
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AN/ASQ-233 MAD P-3C III Retrofit
Current AN/ASQ-233 System
MAD On-line/Off-line Off-line
Off-Line WRAs 16 2 Space (cu. Ft.) 4.7
1.2 Weight (lbs.) 143 28 Power (Watts) 450
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MAD Maneuver Programmer SG-887 / ASW-31
Computer
Indicator
CGA
Vector Sensor
Output Coils(3)
AMP/Power Supply
Control


ASA-65
AN/ASQ-81 Sensor
AN/ASQ-81 Amplifier
AN/ASQ-81 Control
ASQ-81(V)
AN/ASA-64 Processor
Control
Amplifier
RO-32 Recorder
ASA-71
Current P-3C III MAD System
Processor/Control/ Display
Sensor
AN/ASQ-233 MAD
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Spectral Densities