”The laser a solution without a problem””The laser, a solution without a problem”

Anne Thorne, 1960

Summary of group activities

Laser Technology Laser-matter Interaction Laser Technology, Laser matter Interaction and its Applications

Dr Khaled Abdelsabour ElsayedDr. Khaled Abdelsabour ElsayedPhysics DepartmentFaculty of ScienceFaculty of Science

Cairo University

October 20, 2011 2

OutlineOutline

What is Laser Induced Breakdown Spectroscopy (LIBS)?

Basics of Laser Induced Breakdown Spectroscopy (LIBS)

Design and construction of Q-Switched Nd: YAG Laser System for LIBS Measurements

LIBS applications in Combustions, Archaeology, biology, ..

Lidar systems: Elastic Backscatter Lidar Signal to Noise RatioLidar systems: Elastic Backscatter Lidar Signal to Noise Ratio Improvement for Daylight Operations

Fabrication and size control of metal nanoparticlesFabrication and size control of metal nanoparticles.

October 20, 2011 3

What is LIBS?What is LIBS?

LIBS is a physical technique applied to a typical problem of analytical chemistry, i.e. the determination of the elemental compositions of materials

Basics of Laser-Induced Breakdown Spectrometry (LIBS)Basics of Laser-Induced Breakdown Spectrometry (LIBS)

l i i

Elements of LIBS

1. Laser-sample interaction

2. Separation of material ⇒ Ablation2. Separation of material ⇒ Ablation

3. Plasma formation ⇒ Vapor ionization (breakdown)

4. Plasma spectral analysis ⇒ Emission spectrometry

5

1. Laser-sample 1. Laser-sample Laser beam (pulsed and focused)

1. Laser sample interaction

1. Laser sample interaction

Sample

100 fs

6

Laser beam

absorption Samplep

100 ps

7

2. Ablation2. AblationLaser beam

orp

tion

vapor

abso

crater sampleabsorptionabsorption

1ns

8

3. Breakdown3. Breakdown

Shock wave

plasmap

ions

electrons

atoms >1018 cm-3

2ns -20 ns

molecules

particles>15000 K

9

Laser pulse endsLaser pulse ends

20ns -100 ns

10

Plasma CoolingPlasma Cooling

100 ns-1 μs

11

Plasma CoolingPlasma Cooling

1 μs- 100 μs

12

Plasma endsPlasma ends

1ms

13

The evolution of the intensity emission fromThe evolution of the intensity emission from a laser induced plasma

October 20, 2011 14

Laser pulses

tl

Laser pulses

tPlasma emission

tp

td ti

Signal integration

d i

g g

t T l idth f l ltl : Temporal width of laser pulsetp : Plasma durationtd : Delayti : Integration time

October 20, 2011 15

i g

Laser Wavelength: 1064 nmLaser Wavelength: 1064 nm

35000

25000

30000

0.6

547.

7

2.9.9

td= 0 ns

15000

20000

Mo

(I) 5

50

Ni (

I) 5

Fe (I

) 542

Cr (

I) 54

0.

10000 td = 500 ns

540 542 544 546 548 550 552 5540

5000

td = 1000 ns

Wavelength (nm)

LIBS spectra* 25 l h t

October 20, 2011 16stainless steel

* 25 laser shots

* Integration time: 500 ns

Components and phenomena affecting LIBS analysis

SampleReflectivity, heat capacity, melting and boiling point,thermal conductivity etc.

Laser Pulse energy, duration, spot size, wavelength

Plasma Surrounding atmosphere(pressure, nature)

S t t Échelle spectrometer Czerny-TurnerSpectrometer Échelle spectrometer, Czerny Turner,Rowland circle

October 20, 2011 17Detector IPDA, ICCD, Interline CCD,gated CCD, PMs

Mechanisms involved in the laser-material interactionMechanisms involved in the laser-material interaction

Laser-gasLaser-gas•Photon absorption and scatteringp g

•Breakdown •Plasma formation

•Laser-plasma interaction (inverse Bremsstrahlung,photoionization…)Laser plasma interaction (inverse Bremsstrahlung,photoionization…)•Shock wave formation

•Hydrodynamic expansion•Unidentified mechanismsUnidentified mechanisms

Laser-solid targetLaser-solid target

•Reflection (time dependent)•Melting•Vaporization•Vaporization•Crater formation •Stress wave in the target•Plasma-material interaction (radiative heating pressure)•Plasma-material interaction (radiative heating, pressure)•Ejection of solid fragments or ions target

4. Plasma spectral analysis4. Plasma spectral analysis

Power Supply

Nd:YAG Laser SHG Device

ContinuumSurelite I

PrismAlignment

SureliteSSP

Beam Splitter

FocusingOptics

Energy Monitor

SpectrographX-Y-Z

TranslatorPlasma

CollectionOptics

CCDDetector X-Y-Z

TranslatorController

Pulse and delayygenerator

LIBS analysis capabilities

•Metals

A large range of matrices can be studied by LIBS

SOLIDSMetals

•Ceramics

•Semiconductors

•Molten metals, salts and glass

•Industrial effluents

LIQUIDS

•Polymers

•Pharmaceuticals

•Process liquids

•Pharmaceutical preparations

•Teeth

•Soils

•Biological fluids

•Water (Environment)

C ll id•Minerals

•Bacteria on agar substrate

M t l i d i t •Industrial exhaust streams

•Colloids

GASES

•Metals immersed in water

•Wood, paper

Industrial exhaust streams

•Combustion environments

•Aerosols in ambient air

October 20, 2011 20•Proof-of-concept for detection of

chemical warfare agents

LIBS advantages• Applicable to every sample type

• Solids• Liquids• Gases• Aerosols• Insulators/Conductors/Semiconductors• Refractory samples• Melted material

Room temperature and atmospheric pressure operation• Room temperature and atmospheric pressure operation• Multielemental capability• Sample preparation unnecessary• Low sample requirements (ng-μg/pulse)• Low sample requirements (ng μg/pulse)• Fast

LIBS drawbacks

•Detection limits (order of ppm) •Precision and accuracy •Some elements are hardly detectable (Cl, S, …)

21

Surface sensitivity: Beam focal conditions

Laser beam

Focusing lensWD working distance

Focusing lens

WDf

g

f lens focal length

g lens-to-sample distance

sampleWD = g - f

WD = 0 WD > 0WD < 0

crater

d

h

r2r1 r3> <

craterh

Aspect ratio r = d/h

October 20, 2011 22

Detection of surface impurities on monocrystalline siliconNd:YAG Laser @ 532 nm, 5 mJ pulse-1

WD = - 5 mm WD = 0 mm WD = + 5 mm

sity

(a.u

.)

(I)nsity

(a.u

.)

)sity

(a.u

.)

Si (

I)

Inte

n s

Cu

(I)C

u (I)

Ca

(II)

Ca

(II)

Al (

I)A

l (I)

Si (

Inte

n

Cu

(I)Cu

(I

Ca

(II)

Ca

(II)A

l (I)

Si (

I)

Al (

I)Inte

ns

300 305 310 315 320 325 3300

Wavelength (nm)300 305 310 315 320 325 330

0

Wavelength (nm)300 305 310 315 320 325 330

0

Wavelength (nm)

October 20, 2011 23Single-shot spectra

Surface sensitivity : effect of pulse energySurface sensitivity : effect of pulse energy

E E E< <E1 E2 E3< <

Laser beam

dFocusing lens

craterh

sample

r1 r2 r3~ ~

October 20, 2011 24

1 2 3

08.2

309.

3

Laser Effect of pulse energy

6 Si (

I) 28

8.1

) 328

.1

338.

3

Al (

I) 30

Al (

I) 3

Al2O3 , ≅1,2 μm coating by pulsedSi

asebeam

(I) 2

57.5

Al (

I) 26

6.03

Au

(I) 2

67.6

Mg

(II) 2

79.5

Mg

(I) 2

85.1

Ag

(I )

Ag

(I) 3

Al (

I) 35

8.8

Au

(I) 3

12.3

2.5 mJ/pulse

laser deposition

u.)

Al A M

nsity

(a.u

1.3 mJ/pulse

Inte

n

308.

2

309.

3

0.7 mJ/pulse

Al (

I)

Al (

I)

October 20, 2011 25Wavelength (nm)240 370

D i d t ti f Q S it h d Nd YAG L S tD i d t ti f Q S it h d Nd YAG L S tDesign and construction of Q-Switched Nd: YAG Laser System for LIBS Measurements

Design and construction of Q-Switched Nd: YAG Laser System for LIBS Measurements

The aim of this work is to design and build Nd:YAG laser system to meet the following requirements:

i. Able to deliver peak power greater than that needed for breakdown threshold.ii. Multi-pulse laser source since multi-pulse laser system enhance the signal intensities. iii. Provide a potential compact, robust laser source for portable LIBS system. p p , p y

A single passive laser shot contains train of pulses is required. Each pulse should be in the range of 1 MW/cm2. Assuming the pulse width of the passive Q-switch is in the range of nanoseconds, and the energy of each pulse is about or more than 25mJ; the total Q-switched energy of each shot should be in the range of 100-170 mJ

October 20, 2011 26

The Overall System Block Diagram

Main Power Supply

CoolingSystemPower Supply System

Simmer Power Supply

Laser Head700 V –1 kV

Rod, Flashlamp, Reflector, Resonator.

PFNLaser

Control Trigger

Delay

October 20, 2011 27

Laser ResonatorLaser Resonator

The selection of the cavity configuration depends upon the following three factors diffraction loss,

d l dmode volume and ease of alignment. The plane parallel cavity configuration is very useful for pulsed solid state lasers

large mode volumelarge mode volume, no focusing inside the laser cavity. Disadvantage: diffraction losses can be easily overcome by high laser

medium gain

October 20, 2011 28

medium gain. .

2a

r /r = 1 2

Pump cavity

RL

2C2b

rr /rL = 1.2C= (a2 – b2)1/2 , e = C/a

October 20, 2011 29

Driving circuit of flashlampDriving circuit of flashlamp

Component

Value

C1 0.2µF/600vC2 101µF/2.0kvL2 99µH (60 turns)

Øw2 = 1.5mmL1 (3 turns) Øw1 =

1.5mmD1-D4 1N5408

C3 0.47 µF /600VR1,R2 150 kΩ/1W

R3 10 kΩ/1W

October 20, 2011 30

Laser CharacteristicsLaser Characteristics

R l h t f th Nd YAG l t Temporal profile of passively Q-switched laser pulsesReal photo of the Nd:YAG laser system

October 20, 2011 31

System validation

250000

300000

350000

CaI

Fe

5

6

7

3 )

150000

200000

250000

Ca

Ca

Fe

Fe

Fe

Fe

Inte

nsity

(a.u

.)

1

2

3

4

Nex

1018

(cm

-

400 405 410 415 420 425 430 4350

50000

100000

Mn

Sr

Sr I

Cr Fe

Ca

Ca

Fe Fe

Fe

F

Fe

Fe

Fe

Fe

Fe

Fe Fe

FeFe

Fe Fe

Fe

Fe

0 500 1000 1500 2000 2500 3000

0

1N

Time (ns)Electron density temporal evolution (Ne)

Wavelength (nm)

Emission spectra from mamlouki brown ceramic body ofarchaeological samples

Electron density temporal evolution (Ne)

10000

11000

12000

C l i

7000

8000

9000

10000

T (K

)Conclusion

Multipulse passive Q-switched Nd: YAG laser system has been designed and build.

0 500 1000 1500 2000 2500 3000

6000

Time (ns)

Temporal behaviour of the plasma temperature

To validate the the laser system, it was used in LIBS experiment

October 20, 2011 32

Temporal behaviour of the plasma temperature obtained via Boltzmann equation

Assessment of LIBS diagnostics of plasma using the hydrogen Hα- line at different laser energiesAssessment of LIBS diagnostics of plasma using the hydrogen Hα- line at different laser energies

Assess the measurements of the laser produced plasma electron density usingAssess the measurements of the laser produced plasma electron density usingthe hydrogen Hα-line at 656.27 nm associated with the emitted spectra fromaluminium target at different laser energy in the range from 175 up to 600 mJ.

Hα-line at 656.27 nm is well isolated, survive for longer times, has relativelylarge FWHM, and self absorption free

October 20, 2011 33

Experimental SetupExperimental Setup

October 20, 2011 34

2 5

3

3.5x 1017

cm.3 )

Results

1

1.5

2

2.5

ectro

n de

nsity

( e

/

10 15 20 25 30 35 40

0.5

1

Laser energy (mJ)

Ele

The variation of the measured electron density The variation of the calculated electron density from lines of the Al II with laser energy in comparison with the values from the Ha linee a at o o t e easu ed e ect o de s ty

utilizing the Ha line with the laser energy gy p a

(a) Multi-line Saha-Boltzmann plots after correction of Al I and Mg I, II lines against self absorption (Upper and lower solid lines, respectively). (b) Multi-elemental Saha-Boltzmann plot after correcting the Mg lines by their relative concentration.

October 20, 2011 35

The overall variation of the calculated electrontemperature utilizing the multi-elemental Saha-Boltzmann plot after correction of spectral linesagainst self absorption with the laser energy

Conclusion

The electron density of the plasma was measured by using the H -line and the Al linesThe electron density of the plasma was measured by using the Hα line and the Al lines as well as from Mg lines in the range of laser energy from 170 to 600 mJ under the same conditions.

Linear increase in the electron density was found. In contrast to Al I and Mg I, II lines, the spectral lines of Al II were found to be self absorption free. This may be attributed to the large concentration of atoms in the ground state of the inherent resonance transitions.

A correction to the lines intensities at the central emitted wavelength was done utilizing the ratio of the electron densities from the different lines to that measured from the H -linethe ratio of the electron densities from the different lines to that measured from the Ha line. A compatible Saha-Boltzmann plot of the spectral line intensities could be obtained only after correction of self absorption effect, which turned out to be crucial in any reliable characterization of plasma

October 20, 2011 36

Experimental investigation of double pulse laser induced plasma spectroscopy in bulk waterspectroscopy in bulk water

October 20, 2011 37

Double pulse laser induced plasma spectroscopy in bulk water

Nd:YAG

Master

45o Mirror

O i l1064 nmMaster

Nd:YAG

Delay UnitTelescopic

system

L1L2B.S

Optical Fiber

B.SNd:YAG

Slave

L1B.SB.S

1064 nm

Driver Echelle Spectrometer

& ICCD

October 20, 2011 38

Temporal evolution of plasma spectra at gate width 10 μs as a function of (a) inter-pulse delay at gate delay 166 ns, and (b) gate delay at inetr-pulse delay 30 μs.

October 20, 2011 39

C b ti P j tC b ti P j tCombustion Projects Combustion Projects

"Detailed Studies of Premixed and Partially Premixed Burners Using Highly Advanced Laser-Based Techniques"Combustion Division, Lund University, Lund - SwedenCombustion Division, Lund University, Lund Sweden

2006–31/12/2009(SIDA) Swedish International Development Agency – Sweden

"Computational and Experimental Studies of the Structure and Dynamics of Premixed Flame Kernels under Turbulent Conditions“North Carolina State University, North Carolina, USA Prof. Tarek Echekiki, North Carolina State University

2009–31/12/2011US-Egypt funding - STDF

October 20, 2011 40

Local equivalence ratio measurements inLocal equivalence ratio measurements inLocal equivalence ratio measurements in turbulent partially premixed flames using laser-

induced breakdown spectroscopy

Local equivalence ratio measurements in turbulent partially premixed flames using laser-

induced breakdown spectroscopyThe aim of this work is to study the application of the double pulse LIBS technique for

turbulent flame measurements The technique is applied to two turbulent natural gas

induced breakdown spectroscopyinduced breakdown spectroscopy

turbulent flame measurements. The technique is applied to two turbulent natural gas partially premixed flame stabilized by conical nozzle.

Quantitative measurements of the elemental mass fractions and equivalent ratio.Quantitative measurements of the elemental mass fractions and equivalent ratio.

Equivalence ratio, φ, which is defined as the ratio between the stoichiometric air-to-fuel ratio and the actual air-to-fuel ratio. So, at φ = 1 the mixture is stoichiometric, i.e. the air is , φ ,just enough to burn the fuel, while for φ < 1 the mixture is lean, i.e. excess air, and for f > 1 the mixture is rich, i.e. excess fuel.

Equivalent ratio and mixture fraction are important parameters used in combustion models to understand the combustion process and to describe and predict flame.

October 20, 2011 41

Experimental SetupExperimental Setupp pp p

3 5 0

N I

2 0 0

2 5 0

3 0 0

ity (a

.u)

5 0

1 0 0

1 5 0

N I

In

tens

H IH I

C I

N IO I

2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0

0

W a v e le n g th (n m ) E=100mJ, pulse width 8nsDelay between two pulses=250nsGate width 10000ns, Gate delay = 1000ns from the 2nd laser, y

October 20, 2011 42

0 6

0.8

1

1.2

zed

Sign

al

0 6

0.8

1

1.2

zed

sign

al

O 777 N 745Results

0

0.2

0.4

0.6

0.2 0.205 0.21 0.215 0.22 0.225 0.23 0.235

O C t ti

Nor

mal

iz

0

0.2

0.4

0.6

0.66 0.68 0.7 0.72 0.74 0.76 0.78

Nit C t ti

Nor

mal

iz

a b

Oxygen Concentration Nitrogen Concentration

0.6

0.8

1

zed

Sign

alH656

0 6

0.8

1

1.2

zed

Sign

al

H485

0

0.2

0.4

0 0.005 0.01 0.015 0.02 0.025

Nor

mal

iz

0

0.2

0.4

0.6

0 0.005 0.01 0.015 0.02 0.025

Nor

mal

iz

c d

Hydrogen Concentration Hydrogen Concentration

0.8

1

1.2

ed S

igna

l

C 247

0

0.2

0.4

0.6

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Nor

mal

ize

e

Carbon Concentration

The calibration curves for the lines (a) O at 777 nm, (b) N at 745 nm, (c) H at 656 nm, (d) H at 485 nm and (e) C at 247 nm.

October 20, 2011 43

Flam Measurements

The mixture fraction, ξ,

⎞⎛=

Aφξ

st⎟⎠⎞

⎜⎝⎛+

FAφ

ξ

where (A/F)st is the stoichiometricwhere (A/F)st is the stoichiometric air-to-fuel ratio and is equal to17.167 in the present flames with natural gas

Figure 8 Radial profiles of the average and rmsf h i l i i b h fl ( ) φ

Figure 9 Radial profiles of the average and rmsf h i f i i b h fl ( ) φof the equivalence ratio in both flames at (a) φ

= 3 and (b) φ = 4of the mixture fraction in both flames at (a) φ =

3 and (b) φ = 4Conclusion

LIBS technique is able to measure the local equivalence ratio in turbulent environment from single shot with double pulse laser

October 20, 2011 44

from single shot with double pulse laser.

Laser-Induced Breakdown Spectroscopy Technique inLaser-Induced Breakdown Spectroscopy Technique inLaser Induced Breakdown Spectroscopy Technique in Identification of Ancient Ceramics Bodies and GlazesLaser Induced Breakdown Spectroscopy Technique in Identification of Ancient Ceramics Bodies and Glazes

The aim of this work is to use Laser Induced Breakdown Spectroscopy (LIBS) as a promising non-destructive technique for the identification of the colored glazes, and clay’s bodies of Fatimid ceramics ancient artifacts. co o ed g a es, a d c ay s bod es o a d ce a cs a c e a ac s

The scientific examination of ceramics may be helpful in unravelling the history of ancient shards, particularly as the process of its production such as y p y p pfiring condition and temperatures.

The analysis of pottery, ceramic bodies and glazed coatings is required in order to structure the conservation or restoration of a piece.

October 20, 2011 45

Experimental setupExperimental SetupExperimental Setup

Power Supply

Experimental setupp pp p

Continuum

Surelite I

Beam splitter

Nd:YAG Laser

Echelle Spectrograph

Beam splitter

Focusing Optics

X-Y-ZPlasTrigger In Translatorma

ICCDDetector

X-Y-Z

5

fiber

X Y ZTranslatorController

samples

October 20, 2011 46

32000

g II

Mg

IIResults

20000

30000

y(

)

SiI

Pb I

Pb

I

Pb I

Fe I

16000

20000

24000

28000 Si I

Pb I

Mg

M

II IFe

IIy(

)

360 370 380 390

10000

Ti I Pb

I

Fe I

Fe I

Fe I Fe

I

Fe I Fe

I

Fe I Fe

IM

g I

Mg

I

Si II

Fe I

Pb

I

P

Fe I

Fe I

Fe I

Fe I

Fe I

258 261 264 267 270 273 276 279 282 285 288

0

4000

8000

12000

Cr I C

r IMg

I

Fe I

Sn

I

Pb I

Sn IS

n I

Sn I

Pb I

Mg

I

Sn

I

Fe II

Fe II

Fe II

Fe I

Fe II

Fe II

Pb I

Pb

Al I Fe

IIFe II

Fe II

Fe II

Fe II

360 370 380 39

Wavelength (nm)

258 261 264 267 270 273 276 279 282 285 288

Wavelength(nm)

30000

20000

30000

Fe I

Fe I

Fe I

Ca

I C

a I

I

Cu

I

Cu

I

Fe I

Fe I

Inte

nsity

(a.u

.)

321 324 327 330 333 336 3390

10000

Fe I Co

I

Cu

I

Ca

I

Sn I

Cu

I

Na

I Cu

I

Cu

I

Cr I

Sn I

Cu

Fe I

Fe I

Fe I

Fe I Pb

I

Wavelength (nm)

LIBS spectrum of glaze sample no 1,2,3

October 20, 2011 47

ConclusionThe information extracted from LIBS results suggested that LIBS can be employed to

d i / fi h d f i fdetermine/confirm the date of certain types of pottery.

The scientific examination of ceramics may be helpful in unravelling the history of ancient shards, particularly as the process of its production such as firing condition andancient shards, particularly as the process of its production such as firing condition and temperatures.

The analysis of pottery, ceramic bodies and glazed coatings is required in order to t t th ti t ti f istructure the conservation or restoration of a piece..

October 20, 2011 48

A comparative study of laser cleaning ofA comparative study of laser cleaning of archaeological inorganic materials with

traditional methods

•All samples were excavated from El-Fustat excavation in Old Cairo.

Samples description

•El-Fustat founded as a first capital of Islamic Egypt (21AH / 641 AD). •The samples may be belong to Abbasid period (132 AH / 750 AD).•The samples collected were glass, pottery and bronze contaminated with diff t d itdifferent deposits

October 20, 2011 49

Al-Fustat Location

(East Nile)(East Nile)

Laser Cleaning (Pottery sample)Laser Cleaning (Pottery sample)

(a) (b)

area of pottery sample no 1Fig. (a-b) Shows the area of pottery sample no.1

area of pottery sample no.1after cleaning by laser with

after cleaning by laser (magni.12 X- 25 X)

Traditional cleaning (Pottery sample)

(b)(a)

Figs.(a-b) Shows staining and erosion in surface of pottery sample no.1 after cleaninbg

with chemicals

he area of pottery sample no. 1 after cleaning by

Comparative study of laser cleaning and traditional cleaning (Pottery sample)

(a) (b)(b)(a)

Fig. (a-b) Shows the area of pottery sample no.1 after cleaning by laser (magni.12 X- 25 X)

Figs.(16 a-b) Shows staining and erosion in surface of pottery sample no.1 after cleaninbg with chemicals

Laser Cleaning (Pottery sample)Laser Cleaning (Pottery sample)

(a) (b)

Fig Shows the area of pottery sample no 2 after cleaning by

laser

Figs.(a-b) Shows the surface of pottery sample no.2 after cleaning by laser with magni. 12X- 50X

The impact of the telescope selection and diaphragm The impact of the telescope selection and diaphragm

Elimination of background noise in the daytime measurements in case where full

p p p gdesign in LIDAR signal-to-noise ratio improvements

p p p gdesign in LIDAR signal-to-noise ratio improvements

g yoverlap between laser beam and receiver telescope field of view is necessary. Range and sensitivities of lidar measurements in daylight are limited bysky background

noise (BGS) Raman lidar signal is relatively weak, this often restricts Raman lidar measurements to

nighttime where BGS is absent Significant improvements in Lidar signal to noise ratio (SNR) and attainable lidar ranges

b bt i d b i i i i th d t t d k BGS hi h d i t ll th thcan be obtained, by minimizing the detected sky BGS which dominates all the other forms of noisea diaphragm design and the receiver telescope proper parameters selection can reduce the detected sky background noisereduce the detected sky background noise.With moving the diaphragm position and select the proper telescope F# and field-of-view (FOV), the sky noise reaching the detector is minimized. Results show as much as a factor of 200% improvement in signal-to-noise ratio, as wellResults show as much as a factor of 200% improvement in signal to noise ratio, as well as the corresponding range improvement.

October 20, 2011 55

Lidar equation:

⎟⎞

⎜⎛

∫RcA τ

Lidar equation:

⎟⎟⎠

⎞⎜⎜⎝

⎛−= ∫ L

LLL

oLL dRRkcRR

RA

PRP0

2 ),(2exp2

)(),()(),( λτ

ξλβλξλ

Where, P is the total scatter laser power received from a distance R, PL represents theaverage power in the laser pulse, Ao/R2 describes the solid angle of the receiver opticso(Ao is the area of the telescope primary mirror), ξ(λL) denotes the receiver’s spectraltransmitter factor, β is the volume backscatter coefficient, cτ represents laser pulselength (c is speed of light, τ is Laser pulse rectangular duration), k: Atmosphericextinction coefficient The smaller the value of ξ(R) is the smaller the return signal andextinction coefficient. The smaller the value of ξ(R) is the smaller the return signal andthe smaller SNR particularly for short distances. GF can be defined as the ratio of theenergy transferred to the photodetector to the energy reaching the telescope primarymirror, Edet /Escat

6.

October 20, 2011 56

Geometric Factor in Monostatic Biaxial Lidar

OverlapArea

The image displacement isaccording to the distance ‘L’between the laser andtelescope optical axis and the

r 2 r 1

LFOV

Y1Receiver

Z

w max

p paltitude ‘R’.Lidar specifications used in thesimulationd = 0 L = 200 mm

dX1

LaserFOV

Laser

Fig. 2. Schematic diagram of elastic Biaxial Lidar Showing overlapping between field of view

of receiver telescope and laser beam

Z

R m

ax m

in

Telescope

L 200 mmWo = 5 mmr0 = 177.8 mmӨ = 0.7 mradf = 1000-4000 mmR 0 5 kFig. 1. Overlap Area Calculations of receiver telescope and laser beam

The range ‘R’ increases, there will be a point ‘Ro’ where the first intersection between the laser beam and the telescope FOV, then partial overlap, and

X

R

f

Telescope

Laser

L

Rmin = 0.5 km Rmax = 25 km

and the telescope FOV, then partial overlap, and finally complete overlap

October 20, 2011 57

ZMinimizing the detected BGP using GF

OL

Overlapping area /image area formed near f

RfDoeff /=φ

ApertureFOV

0Im

)( ==area

areaOLRξ

R2

R3

R4

Aperture(field stop)

0=areaOL 0)()( == RARA oeff ξwhere effective telescope area

Lo

Lboto

θDo

fR1

LaserTelescope

X

minimizing the detected BGP. That can be achieved by moving the commonplace aperture (Do) center from the origin (fo ) some distance to the left (depend on the object height) and reduces the aperture size from Do to smaller diameter Ds LaserTelescope

Biaxial Lidar: overlapping between effective FOV of receiver telescope (diameter of to) and laser beam (initial diameter Lo) and aperture diameter Do

ooeff fD /=φ to sseff fD /=φ

October 20, 2011 58

Results

Lidar images for range 500m-5km Lidar images for range 5km-25km

The red circle is the round diaphragm of 2mm diameter The blue Circle is the proposed diaphragm design

The red circle is the round diaphragm of 2mm diameter The blue Circle is the proposed diaphragm design

October 20, 2011 59

Image’s size versus telescope focal length for different lidar ranges. Effective FOV (φeff) is shown no big different in the higher range for a variety of f. Normalized φeff with respect to φeffof (f = 4m) is also shown

Telescope F

Lidar range ‘R’ Aperture diameter

φeff = DL /F φeff(Norm)

SNRImp

of (f 4m) is also shown

F diameter (Norm)From (km)

To (km) DL (mm) (mrad) % %

4 m 0.5 5 4.7 1.175 100 05 25 3 0.75 100 0

3 0 3 4 1 13 96 23 m 0.5 5 3.4 1.13 96 25 25 2.1 0.7 93 3.6

1.7 m 0.5 5 1.8 1.058 90 5.45 25 1.4 0.7 93 3.6

1 m 0.5 5 0.85 0.85 72 17.85 25 0.6 0.6 80 11.8

October 20, 2011 60

Conclusion:

Classical design of lidar receiver subsystem does not account for receiving optics that are placed on line forming an angle with the imaging plane of receiver telescope. (small GF)

Proposed design attain significant lidar SNR improvements by minimizing the detected sky BGN by setting the receiver round aperture in the proper position with a smaller size.

Lidar system with small telescope F# is much better in reducing BGS particularly for shortLidar system with small telescope F# is much better in reducing BGS particularly for short distances. Smaller FL to ensure having the minimum FOV that accepts all return signals for the entire ranges.

results show that a receiver telescope with small F# (1 m) can significantly increase the SNR of factor of 200% as compared to telescope with big F# (> 4 m)

200 % SNR improvement is can be translated into equivalent reduction of the required200 % SNR improvement is can be translated into equivalent reduction of the required averaging time by a factor of (1/2)1/2

Experiments are planed to test the overlap form factor with the end goal to design an optimized automated variable diaphragm system.

October 20, 2011 61

Elastic Backscatter Lidar signal to Noise Ratio I t f D li ht O ti P l i ti

Elastic Backscatter Lidar signal to Noise Ratio I t f D li ht O ti P l i tiImprovement for Daylight Operations: Polarization

Selection and AutomationImprovement for Daylight Operations: Polarization

Selection and Automation

Motivation

Most lidars are range and sensitivity limited in daylight operation by skyMost lidars are range and sensitivity limited in daylight operation by skybackground noise.

Limits to what can be achieved with narrow band filters have been reached.Limits to what can be achieved with narrow band filters have been reached.

Proposed approach reduces detected sky background by making use of factthat sky background is partially polarized and suitable polarization selectionf d t ti f l i d lid t d ifor detection of polarized lidar returns reduces noise.- Collecting data without attendance- Fast and accurate lidar operations

Applicable for Different lidar- Applicable for Different lidar- Globalization.

October 20, 2011 62

Sky background suppression geometryS y bac g ou d supp ess o geo et y

October 20, 2011 63

Block diagram of polarization experiment set upfor elastic monostatic biaxial lidar (mobile lidar)for elastic monostatic biaxial lidar (mobile lidar)

1. Elastic monostatic biaxial backscatterlid CCNY (l i d 3 94 W

Receiver

Llidar system, at CCNY, (longitude 73.94 W,latitude 40.83 N), at 532 nm.

2. The lidar transmitter was a 10 Hz Q-Switched Nd: YAG MDL Continuum TelescopeSwitched Nd: YAG_ MDL ContinuumSurelite laser.

3. The receiver was a 14” (355.6 mm)diameter CM-1400 Schmidt-Cassegriant l ith f l l th f 153 9”

½ Wave plate

Transmitter

Laser

telescope with a focal length of 153.9”(3910 mm) coupled to a PMT R11527PDetector with a 1 nm bandwidth optical532F02-25 Andover filter centered at 532

Filter

To rotate outgoing signal polarization

Lens

Polarizing Beam Splitter rotated to match min BGN

532F02 25 Andover filter centered at 532nm wavelength.

4. The lidar output at 532 nm is linearlypolarized and has a 0.5 cm beam diameter,0 5 d di l i f 100 λ=532 nm

Detector

0.5 mrad divergence, pulse energies of 100mJ, pulse width of 3 ns, a ½ wave platerotation of polarization of outgoingsignal to match received polarization

October 20, 2011 64

signal to match received polarization

Experimental range dependent SNR for:Maximum and minimum polarization orientations forMaximum and minimum polarization orientations for

maximum observed Gimp

1. SNR improvement of 10 wasobtained which resulted in anincrease in lidar operating

20 Max BGNMinBGNp g

range from 9.38 km to 12.5kmis observed (a 34%improvement).

14

16

18

m)

Min BGN

⎟⎟⎠

⎞⎜⎜⎝

⎛≈⎟⎟

⎠

⎞⎜⎜⎝

⎛+=

Min

Max

Min

Maximp N

NNN

G2

1

2. Alternatively, for a given lidarrange, say 9 km, the SNRimprovement was 250%.

10

12

14

(10 938k )

Altit

ude

(km

(10, 12.5 km)

(6:30PM)3. Note that, this improvement

depends on the angle betweenth di ti f l di ti

6

8

(10, 9.38 km)

the direction of solar radiationand the lidar axis. For verticallidar this is the solar zenithangle

0 5 10 15 20 25 30 35 40 45 504

SNR

October 20, 2011 65

angle.

Gimp at detection wavelength of 532 nm as function of local time, and solar zenith angle , g

8

9

10 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

⎟⎟⎠

⎞⎜⎜⎝

⎛≈⎟⎟

⎠

⎞⎜⎜⎝

⎛+== MaxMaxMax

imp NN

NN

SNRSNRG

2

1

4

5

6

7

Gim

p

Experimental min Ratio at 11:30 AM

Gimp vs. Local Time

⎟⎠

⎜⎝

⎟⎠

⎜⎝ MinMindUnPolarize

imp NNSNR

0

1

2

3

Experimental min Ratio at 11:30 AMzenith angle = 52.718

Min zenith angle = 51.967at 12:10 PM

Local Time

9

10

Before Solar Noon After Solar Noon

The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

Local Time , Feb 19,

4

5

6

7

8

Gim

p

Gimp vs. zenith angle

0

1

2

3

4

50 55 60 65 70 75 80 85 90 95

Min zenith angle = 51.967at 12:10 PM

zenith angle

October 20, 2011 66

50 55 60 65 70 75 80 85 90 95

Zenith Angle Feb 19,

Solar azimuth angle impact on lidar SNR

320

Polarization orientation for vertical lidar relative to solar azimuth angle needed to achieve minimum BGS

260

280

300

Azimuth angle Polarizer rotating angle

Polarizer rotating angle

180

200

220

240

Ang

le (D

egre

e)

Azimuth angle

120

140

160

180

9:10 10:10 11:10 12:10 13:10 14:10 15:10 16:10 17:10 18:10 19:10

The minimum BGS angle closely tracks the azimuth angle as shown above

9:10 10:10 11:10 12:10 13:10 14:10 15:10 16:10 17:10 18:10 19:10

Local Time

•This relationship is important since it allows the system to automaticallyrotate both the transmitter laser and detector polarizer to the known solarposition minimizing the effective BGS.

October 20, 2011 67

AUTOMATED CONTROL SYSTEMTYPICAL INFORMATION EXCHANGE

BETWEEN LIDAR SUBSYSTEMS

Laser

Transmitter

TimerAn appropriate control system, it would then be possible to track h i i BGS b i h

TransmitterPolarizer

Receiver

Anglesource

the minimum BGS by rotating the detector analyzer and the transmission polarizer

i lt l t i i th Analyzer

Environment

Observation

simultaneously to maximize the SNR,

Achieving the same results as Environment

Radar

Data

Achieving the same results as would be done manually as described above.

Figure shows a typical information exchange between lidar devices summarizes the interactions used as the

An integration of an automatedapproach is proposed here

October 20, 2011 68

summarizes the interactions used as the basis for the control model operation.

PROPOSED CONTROLLER INSTRUMENTS

The Intelligent Picomotor net ork can beThe Intelligent Picomotor network can be configured for different motion control applications (User’s Guide: Intelligent Picomotor Control Modules)

Model 8310 Closed-Loop PicomotorModel 8751-C Closed- Loop Driver

October 20, 2011 69

Model 8310 Closed Loop PicomotorModel 8751 C Closed Loop Driver

Conclusions1. SNR improvements obtained for lidar backscatter measurements using

polarization selection to eliminate the dominant polarization componentcan significantly increase the far range SNR as compared to uncan significantly increase the far range SNR as compared to un-polarized detection resulting in range improvements of over 30% for aSNR threshold of 10.

2 This improvement is most significant for large scattering angles which2. This improvement is most significant for large scattering angles, whichfor vertical pointing lidars, occur near sunrise/sunset.

3. Theoretical models simulate the background skylight within the singlescattering approximation was developed and shown to lead to fairlyscattering approximation was developed and shown to lead to fairlyaccurate predictions of the SNR improvement.

4. Asymmetric noise reduction was some times observed and couldpossible explained by an increase in PWV and subsequent modificationp p y qof aerosol optical depth by hydration.

5. since the polarization axis follows the solar azimuth angle even for highaerosol loading, which may be determined using solar positiong y g pcalculators, it is quite feasible to automate this procedure.

6. Automated control system has been developed.

October 20, 2011 70

Fabrication of metal nanoparticles and Laser-Fabrication of metal nanoparticles and Laser-induced morphology induced morphology

Methods:• Metal colloid Prepared by Laser Ablation in aqueous solutionMetal colloid Prepared by Laser Ablation in aqueous solution• or PLD

Target:• Gold• Silver• Zn•Al•. Platinum• Ti• Si

October 20, 2011 71

Metal colloid Prepared by Laser Ablation in aqueous solution

October 20, 2011 72

Some examples of metal colloid Prepared by Laser Ablation in

10mj

Some examples of metal colloid Prepared by Laser Ablation in aqueous solution

1.010mj 20mj 30mj 40mj 50mj 100mj

10

20

30

40

no o

f par

ticle

s

0.5

Abso

rban

ce

4 6 8 10 12 14 16 18 20 22 240

10n

average size (nm)400 500 600 700 800 900

0.0

wavelength (nm)

Gold Nanoparticles, E=50mJ, λ=1064nmabsorbance spectrum of gold nanoparticles prepared in pure water at (10-100 mJ

October 20, 2011 73

Parameters that affect nanoparticles

14

16

18e

(nm

)

Parameters that affect nanoparticles fabrication:

Laser parameters ( wavelength, pulse duration, …..)

10

12

14

Ave

rage

siz

p , )Geometrical parametersType of surrounding media

4 6 8 10 12 14 16 18 20 228

focal length (cm)

dependence of the focal length on the average size Focusing conditionsp g g

F=5cmTarget position Average size (nm) Particle distribution

(nm)Above focusing 8.6 8.3-13.6

Focusing conditions

gAt focusing 8.9 14.7-22.7Below focusing 7.2 8.6-45

F=10cmAbove focusing 8.3 8.1-14.8At focusing 9.8 10-19.3Below focusing 7.9 6.6-16.6e ow ocus g 7.9 6.6 6.6

The average size and the particle distribution of GNPs at different focal length and target positions.

October 20, 2011 74

Pulsed Laser Deposition (PLD)

Fabrication of Gas sensorsZnoTio

October 20, 2011 75In2O3

Thank You…