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