Remote Observations of the Electric Field within Thundercloud:New LIDAR - Based Techniques
The real time measurement of spatial and temporal distribution of the electric field in and around thunderclouds is important for understanding the formation mechanisms of thunderclouds, for predicting the appearance of lightning strokes and for understanding the processes of the cosmic ray electrons acceleration and the bremsstrahlung photons generation caused by the electric field of clouds. Now the electric field meters, used for this purpose, are set on Earth surfaces or installed on balloons. These techniques are limited as they typically provide a single sample at discrete altitudes at one time. LIDAR systems are the main instrument which allows to realize real time remote measurement of the electric field strength and direction with high spatial and temporal resolution. LIDAR systems are based on the absorption and/or scattering of light by the gas, liquid or solid state. Atomic and molecular spectra can be measured very accurately and sensitively using spectroscopy techniques.
Scattering of Electromagnetic Waves
EM wave induced dipole moment
Linear Nonlinear
P ~ χ (1)E + χ (2)E1E2 + χ (3)E1E2E3 + …
Elastic
Non Elastic
GeometricMie
ReyleighBack Raman
Fluorescence
Four Wave Mixing
P ~ χ (3)E1E2E3exp{ i [ΔKr – Δωt ]} ω = ω1 – ω2 + ω3
K = K1 – K2 + K3
I ~ │χ(3)│2 I1I2I3
Four Wave Mixing & Electric Field
1. Difference Frequency Generation
P ~ χ (3)E1E2E ωE = ω3 = 0 => ω = ω1 – ω2
K = K1 – K2
I ~ │χ(3)│2 I1I2E2
Experimentally realized (laboratory)!!!
2. Sum Frequency Generation
P ~ χ (3)E1E3E ωE = ω2 = 0 => ω = ω1 + ω3
K = K1 + K3
I ~ │χ(3)│2 I1I3E2
Experimentally realized (laboratory)!!!
V. N. Ochkin et all. 19951atm, 532nm, 683nm
H2 – 2.4 μm => 20V/cm
Second and Third Harmonic Generation & Electric Field
Electric Field Induced Second harmonic generation (EFISH)
P ~ χ (3)(2ω) E12E
ωE = ω2 = 0ω1 = ω3
I2ω ~ │χ(3)(2ω)│2 I12E2
Third harmonic generation
P ~ χ (3)(3ω) E13
I3ω ~ │χ(3)(3ω)│2 I13
Electric Field
E2 ~ │χ(3)(2ω)/χ(3)(3ω)│2 I1 I2ω ̸ I3ω
Proposed!!!
N2 – ω1 = 4.2 μmO2 – ω1 = 6.3 μmCO2 – ω1 = 7.5 μmH2O – ω1 = 2.7 μm
CARS & Electric Field
Infrared Wave Generationω3 = ωE = 0 ω1 – ω2 = Ω = ωir
Iir ~ │χir(3)│2 I1 I2 E2
Coherent Antistokes Raman Scattering (CARS)ω3 = ω1 2ω1 – ω2 = ωas
Ias ~ │χCARS(3)│2 I1
2 I2
Electric Field
E2 ~ │χCARS (3) / χir
(3) │2 I1 Iir / Ias
Experimentally realized (laboratory)!!!
P. Bohm et all. 20131000 mbar
H2 – 2.4 μm => 20V/cmN2 – 4.29μm => 300V/cm
Comparison of Linear and Nonlinear techniques
Nonlinear spectroscopyAdvantages:Direct measurement of the electric field.High spectral resolution (Limited by laser line-widths).Disadvantages:Required two laser sources.Registration of IR signal (required fast IR detector for spatial and temporal resolution).Strong absorption of the IR radiation by water (required additional investigations).Development for other molecules, atoms, charged molecules, ions, isotopes etc.Development of Nonlinear spectroscopy techniques for remote sensing in situ.
Linear Spectroscopy Advantages:One laser sourceDisadvantages:Electric field measurement via its influence on the spectrum of gases (not direct).Required high resolution spectrometer, including IR.Required large aperture receiving optics.Required (in some cases) high power IR laser.
The electric field remote sensing methodology in thunderclouds need additional investigations and development !!!
Development of Atmospheric Polarization LIDAR System
Laser Emitter (a+b)Receiving Telescope (c),Polarization Separator (d).
Laser Emitter
1 - Convex mirror, 2 – Electro optical Q-Switch, 3 – Diaphragm, 4 – Output polarizer, 5 – laser oscillator pump chamber, 6 – Quarter wave-plate, 7 – Concave mirror, 8 and 16 – Two wavelength mirrors, 9 – Glan prism polarizer, 10 – Flash- lamp driver cables, 11 – mirror, 12 – Cooling system pipes, 13 – Laser amplifier pump chamber, 14 – Flash-lamps, 15 – Second harmonic generator, 17 – Hole for the output beam.
Laser Emitter output beam parametersPulse Energy 1064nm 300-500 mJ 532nm 100-200 mJBeam Divergence <10-4 radPolarization linearity <10-3 Pulse duration 10 nsRepetition rate 10-20 HzOutput beam diameter 112 mm
Polarization Separator
The green points are the separated cross-polarized beams.
Laser Emitter and Receiving Optical System Alignment
Alignment Laboratory Stand
By means of the laboratory stand was aligned: The Laser, including, laser oscillator and laser amplifier. The Laser with Beam Expander (14X). Diode Laser beam with its beam expander (200X). Diode Laser beam optical axis with RT housing tube axis. Receiving Telescope (RT) mirror optical axis with Diode Laser beam optical axis and RT housing axis. Polarization Separator (PS) optical axis with RT Mirror optical axis. PS with cross-polarized beams outputs and RT mirror focus. Signal transportation fibers with cross-polarized beams. Adjustment of PMTs for registration of GLD beam.
The YerPhI LIDAR System
The Laser
Laser Beam Expander
PMTs
Aiming Optics
Receiving Telescope
Laser Cooling Pipes
Flash-lamp Supply Cables
Q-Switch Driver Cables
Laser Emitter Alignment
System Triggering Photodiode
Signal and Supply Cables
LIDAR System
Polarization Separator
Optical Signal Transportation Fibers to PMTs
The Laser
Laser Beam Expander
Receiving Telescope
Laser Emitter Alignment Mount
Polarization Separator
Alignment Mount
PMTs
Registration System
Triggering Photodiode
Stepper Motor
Stepper Motor end Switch
Play-free Gear
Optical Filter Boxes
Laser Emitter Alignment
Registration System
Triggering FiberAiming Optics
Optical Signal Outputs
Laser Emitter Output Energy Control Fibers
Receiving Mirror Focus Finder
The LIDAR Registration and Control System
Triggering Pulse (5nsec/div).
System Triggering PD and its electronics
PMT Power Supplies
PD and PMT Amplifier Power Supplies
NI DAQ BNC Inputs and Outputs
NI USB DAQ
Oscilloscope 500MHz
LIDAR Controllable Parameters
LE beam 1064nm output energy. LE beam 532nm output energy. LE beam repetition rate. LE Q-Switch driver pulse delay. LE beam polarization finder. PS – LE beam polarization angle. Registration delay. LE – RT angle. PMT supply voltage. LIDAR azimuth and elevation. LE cooling temperature.
Stepper Motor Driver
PMT with voltage divider and Signal Amplifier
The YerPhI LIDAR System
Sorry for quality.
Backscattering from the Atmosphere.
Horizontal - 750m/div; Vertical - 20mV/div; Laser - 100mJ;PMT - 2kV; PS ~ 90deg.
First Backscattered Signal Observations
Laser flash-lamp background and Reflected from a wall signal (250m).Horizontal - 30m/div;Vertical signals - 0.1V/div;Vertical trigger - 2V/div;PMT - 0.5kV.
First Backscattered Signal Observations
Scattering from Atmosphere and Clouds. (Hor.-750m/div; Ver.-20mV/div; PMT-2kV; PS-90deg).
First Backscattered Signal Observations
Scattering from Atmosphere and Clouds.Horizontal - 750m/div;Vertical - 50mV/div; PMT - 2kV; PS ~ 45deg).
Planned Investigations in Nearest Future
1. Reyleigh and Mie backscattering:
– Depolarization ratio profile.
2. Raman backscattering N2 (607nm), O2 (580nm), H2O (645nm):
– Depolarization ratio of spectral bands.
3. Electric field under and inside the clouds.
Linear
P ~ χ (1)E1 exp{ i [ K1r – ω1t ]} 1. Power - Absorption, etc.2. Wavelength - Raman, Fluorescence, Stark, Doppler, etc.3. Line-width - Stark, Doppler, etc.4. Polarization - Kerr, Pockels, Faraday, etc.
Polarizationφ = 2π (no - ne) L / λ = 2π B L E1
2 Bwater = 5.2 10-12 cm/V2 For 1000 V/cm and 500m =>φ = π /2 --> λ/4 plate
Cloud TypeLWC (g/m3)
Atmosphere
Cirrus .03
Fog .05
Stratus .25-.30
Cumulus .25-.30
Stratocumulus .45
Cumulonimbus 1.0-3.0
0.1-5.0
LIDARs for CTAGermany France Argentina Spain France Italy ArmeniaMax PlankI (Munich)
U Montpellier2LUPM
Buenos Aires U Barcelona U Montpellier U TorinoU Naples
YERPHI
for MAGIC for HESS CEILAP IFAE/UAB LUPM ARCADEElastic 1064Elastic 532Elastic 355Raman 387(N2)Raman 607(N2)Raman 408(H2O)Raman 645(H2O)Elastic Polar.
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Distance 0.5 - 18 20 0.25 - 10 0.1 - 15 km
LaserSolitonGmbH
QuantelBrilliant 30
Continuum Inlite II-50
QuantelBrilliant
QuantelCFR400
Quantel Centurion
Custommade
Rep. Rate 2000 20 50 20 20 100 10 - 20 Hz 1064nmEnergy 532nm 355nm
-0.005
-
-18065
1256020
360180100
40023090
40186
300-500100-200
-mJ
Pulse width 0.5 5 10 5 7 8 10 nsPolarization Polar. Polar. Polar. Polar. Depolar. Polar.Beam Dia. (Expander) (10x) 6 6 7 20 (10x) 110 (14x) mm
Divergence 0.75 0.5 3.5 (3) 0.3 (1) <0.1mra
dReceiving Mirror Dia. 600 600 6x400 1800 1800 250 250 mm
DetectorHPD
HamamatsuR9792U-40
PMTPhotonis XP2012B
51mm
PMT/HPDHamamatsuH10721-110
25mm
PMT/HPDHamamatsuH10721-100
38mm
PMTHamamatsu
R329P50mm
PMTHamamatsu
R1332Q50mm
PMTFEU-83
FEU-10025mm
Readout GAGE 8265 LICEL LICEL LICEL CAEN NI DAQ