Transcript Laser Magnetometry Using DBR Laser Pumped Helium Isotopes: (LEOS April 24, 2008)

Laser Magnetometry Using DBR Laser
Pumped Helium Isotopes:
Beyond “Juno at Jupiter”
(LEOS April 24, 2008)
Robert E. Slocum, PhD
Chief Technical Officer
Polatomic, Inc.
1810 Glenville Drive
Richardson, TX 75080
(972) 690-0099
Geophysical Service Inc./Texas Instruments
Circled are Cecil H. Green (L) and Robert E. Slocum (R)
Sputnik October 1957
Vector Helium 4 Magnetometer (VHM) sensor concept.
Mariner 4 launch for Mars 11/28/64
Vector Mode Operation
Variable Density Optical Filter
Laser

IR Detector
Exciter
Vector Mode Signal
Signal (Volts)
BS
Circular
Polarizer
Triaxial Helmholtz
Coil System
1.4
1.2
1
0.8
0.6
0.4
0
90
180
270
360
Degrees
• 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.
Vector Implementation
Bias Nulling Field Mode
BS
Circular Polarizer
Laser
Triaxial Helmholtz
Coil System

BF
B0
Sensor
Feedback
Field
IF
Amplifier
Phase
Demod
IR Detector
Exciter
BS
Sweep
Field
IS
Sweep
Osc.
• 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.
V  IF
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.
Parahelium
Orthohelium
23P0
Do (1082.91 nm)
3
2 S1
+1
0
-1
11S0
Fig. 1 Energy level diagram for helium 4.
He4 Cell Sensing Element:
Variable Density Optical Filter –
Magnetically Controlled
He4 Cell
m=+1
HF Exciter
m=+1
m= 0
m=-1
E = h0
Energy
23S1
HF Discharge
m= 0
E = h0
m=-1
11S0
Magnetic Field B0
B0
• 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
m=+1,0,-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.
Optical Pumping
He4 Cell
23P
D0 (1082.91 nm)
Laser
23S1
HF Discharge
HF Exciter
11S0
23P0
0
D0
m=+1
m= 0
m=-1
23S1
E = h0
E = h0
m=+1
m= 0
m=-1
• Pumping produces non-equilibrium distribution of atoms among different energy
levels.
• m=+1,0,-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
m=0,+1.
Scalar Mode Operation
Magnetically-Driven Spin Precession (MSP)
Laser
IR Detector
Exciter
MSP Resonance Curve
Signal (Volts)
Circular
Polarizer
BRF
Helmholtz
Coil System
0.92
0.88
0.84
0.80
0.76
1.36
1.40
1.44
1.48
Frequency (MHz)
• 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.
Scalar Mode Implementation
Magnetically-Driven Spin Precession (MSP)
Circular
Polarizer
BRF
Helmholtz
Coil System
BRF
B0
Laser
Sensor
Amplifier
IR Detector
Phase
Demod
Exciter
Sweep
Oscillator
• Apply periodic sweep to RF oscillator.
• Causes periodic modulation of detector output.
• Phase synchronous demodulation determines 0 .
RF
Oscillator
0
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]}.
Scalar Mode Operation
Optically-Driven Spin Precession (OSP)
OSP Resonance Curve
Circular
Polarizer
Laser
IR Detector
Exciter
Signal (Volts)
0
1.04
1.00
0.96
0.92
0.88
1.36
1.40
1.44
Frequency (MHz)
• 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.
1.48
Scalar Mode Implementation
Optically-Driven Spin Precession (OSP)
0
0
Circular
Polarizer
B0
Laser
Sensor
IR Detector
Amplifier
Invert Out
Phase
Demod
Exciter
Sweep
Oscillator
• Apply periodic sweep to RF oscillator.
• Causes periodic modulation of detector output.
• Phase synchronous demodulation determines 0 .
RF
Oscillator
0
OSP Signal Amplitude v. Frequency
Light Level = 2 mW, Absorption = 15%, Light Axis Perpendicular to Ambient Field
Line Width = 2636 Hz (94 nT)
MSP Signal Amplitude v. Frequency
Light Level = 0.5 mW, Absorption = 15%, Light Axis Parallel to Ambient Field
Line Width = 2610 Hz (93 nT)
3.600
0.900
3.580
0.890
3.560
0.880
Signal (Volts)
Signal (Volts)
3.540
Raw Data
Lorentzian Curve Fit
3.500
Lorentzian Curve Fit
0.860
0.850
3.480
0.840
3.460
3.440
1.370
0.870
Raw Data
3.520
1.380
1.390
1.400
1.410
1.420
1.430
1.440
Frequency (MHz)
OSP RESONANCE
1.450
0.830
1.340
1.360
1.380
1.400
1.420
1.440
1.460
1.480
1.500
Frequency (MHz)
MSP RESONANCE
Comparison of OSP and MSP magnetic resonance
signals for identical laser pump source and helium cells.
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 fourhinged 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.
Omni-directional laser-pumped
sensor and lamp-pumped sensor.
Self-Calibrating Vector
Helium Magnetometer
Photodiode B
He-4
cell
Photodiode A
Optical
Isolator
PM Fiber
Laser
Intensity
Modulator
He-4
cell
Collimating
Lens
λ/2
Polarizing
Beamsplitter
Cubes
λ/4
Tri-Axial
Coils
Technical Objectives for
Self-Calibrating Vector Helium Magnetometer
 Vector field measurement
SENSOR UNIT
 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/√Hz
ELECTRONICS UNIT
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.
15 August, 2005 Learning Data Set
RMSE before = 28.80867
RMSE after = 0.82896
POLATOMIC 2000 SINGLE AXIS GRADIOMETER ON 25 cm SPACING
43-minute data collection period. Standard size cells both channels, Ofc-1 in Ch A, Ofc-2 in Ch B. Gradiometer mode.
Illum A:1.64/1.47/1.39, B:1.67/1.49/1.38 vdc. Dev 2500 Hz. H1A: 870
a rms, H1B: 980a rms. LL ++, Upgraded optics.
3
1 10
Spectral Density, pT per root Hz
100
MAD
10
MCM
1
0.1
0.01
0.01
0.1
1
10
Frequency, Hz
Ch A
Ch B
Ch A - Ch B
Data Period,
Plotted Frequency
Mean Frequencies,
Noise
characteristics
the
POLATOMIC
2000
minutes
resolution, Hz
and Difference
# Samples
# Averages
Ns = 1114112
= 32
Nm = 42.983
PlotRes = 0.012
MeanFreqChA= 1428216.319
based
on Na45
minute
data
collection
period.
FirstPlotPoint
= 0.006
MeanFreqChB
= 1428229.312
MeanFreqChDiff= 12.993
100
Underwater Magnetic and
Electric Fields
MPA and/or UAV
LCS
AUV
Barrier
The Continuous Challenge: Understand and Manage Our Own
Platform Signatures While Exploiting The Enemy’s
AN/ASQ-233 MAD
P-3C III Retrofit
MAD
Maneuver
Programmer
Computer
Current AN/ASQ-233
System
MAD
Indicator
CGA
SG-887 / ASW-31
Vector
Sensor
Output
Coils(3)
AMP/Power
Supply
AN/ASQ-81
Amplifier
Control
Amplifier
Off-Line
WRA’s
16
2
Space (cu. Ft.)
4.7
1.2
Weight (lbs.)
143
28
Power (Watts)
450
111
AN/ASQ-81
Control
ASQ-81(V)
RO-32
Recorder
Off-line
Control
ASA-65
AN/ASQ-81
Sensor
On-line/Off-line
AN/ASA-64
Processor
ASA-71
Current P-3C III MAD System
Sensor
Processor/Control/
Display
AN/ASQ-233 MAD
TRANSITION PLATFORMS
P-3C MAD Upgrade
Fire Scout VTUAV
P-8A
AN/ASQ-233
SUBMARINE DETECTING SET
SH-60 Seahawk MAD Upgrade
Insitu M-ScanTM
The worlds most sensitive airborne magnetometer in flight testing in 2008.
“CAN POLATOMIC SOLVE A MAGNETICS PROBLEM ON YOUR PROGRAM?”
Spectral Densities
AOSP spectral densities
4
10
data 3-4-08
pi pumping
3
10
2.5 mW
coherent subtraction
spectral density (pT/Hz 1/2)
2
10
1
10
1.1946 pT/Hz 1/2
0
10
-1
10
0.058035 pT/Hz 1/2
-2
10
-3
10
-2
10
-1
10
0
1
10
10
frequency (Hz)
2
10
3
10