Lecture 3 Instrumentation Special

8/16/2019 Lecture 3 Instrumentation Special

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. ns rumen a on or op ca

combustion dia nostics


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Laser aser aser sys em

2) Optics

• Lenses

Lens

• o ar zer

• Filters

• Mirrors

• .

3) Detector • CCD-camera

General experimental setup

CCD-camera

• Photomultiplier +or aser agnos cs

• Etc.

Per-Erik Bengtsson


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Laser

g mp ca on y mu a e m ss on o a a on

Attenuationo

=

ooooo

ooooo Amplification

oPumping

100 % mirror ~80 % mirror


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Laser characteristics

• < -1

• Lasers are coherent in hase

• Lasers can be tunable (continuous

wavelength tuning)

• Lasers are highly directional (laserbeam)

• Lasers can be CW or pulsed ( ns, fs, as!)

• Lasers can give very high laser pulses (J)


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• When working (or visiting) in laboratories with

in laser safety.• Some lasers give radiation in the ultraviolet

and infrared regions that can not be seen by

the eye.

•optics and surfaces can give serious damage

.

• IMPORTANT! No erson should take art in

any experiment without having a guide andrelevant protection glasses


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Laser survey

1. Nd:YAG laser

.

. -

. y -

. u - aser


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Princi le for the YAG laser


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Nd:YAG laser

T ical s ecification:

• Pulselength: ~5-10 ns

• Wavelenght: 1.06 m, 532 nm, 355 nm, 266 nm

• Pulse energy @ 532 nm, 500mJ -1J

• Repetition rate: 10-20 Hz

• Linewidth: ~ 0.7 cm-1, 0.1 cm-1(etalon) 0.005 cm-1 (single

mode)

Companies: e.g - Quantel, Continuum, Spectra Physics,Thales


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Nd:YAG laser

Typical applications:• Pumping a dye laser all applications

, ,• Laser-Induced Incandescence (532nm,

1.06 m)


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Excimer laser


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Typical specification:• Pulselength; ~10-15 ns

,• Pulse energy @ 248 nm, ~250 mJ

• Linewidth. 1 -10 cm-1, tunability possible

Companies: e.g - Lambda Physik


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Typical applications:

• Pumping a dye laser all applications

• Raman scattering (248 nm, tunable)

• LIF (248 nm) - OH, H2O, O2, fuel

• LIF (308 nm) – OH, fuel


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Need for a new laser?

Specifications of an Alexandrite laser:

• Tunable (740-790 nm)

• High pulse energy: ~400 mJ (fundamental @ 776 nm) ~

70 mJ 387 ~10 mJ 259 nm

• Long pulse length: ~140 ns

• Single mode (~0.003 cm-1 linewidth)

• Multimode (~ 8 cm-1 linewidth)

Strong potential for CH visualization

using the frequency doubled beam


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Dye laser

In a dye laser the laser medium is a liquid, and the excitation source is alaser, often an Nd:YAG laser. A dye is chosen depending on the desired

wavelength of the output from the laser .


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The dye laser can be

operated in• narrowband mode

(typical linewidth ~0.3

cm-1, and tuneable within

the tuning range of thedye using a grating at the

• broadband mode

(typical linewidth ~150-1

or a grating in zeroth

order)


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Dye laser

To cover all available wavelengths, different dyes are used

u t e n e r g

l a t i v e o u t

R e

Wavelength / nm


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Different approaches for high speed visualization

• Multi YAG/framing camera approach

t

r nary : aser

t

Nd:YAG laser cluster

Specification- max rep rate: ~200 kHz (8 pulses),

max pulse energy ~400 mJ/pulse @ 532 nm

~ 80 mJ/pulse @ 266 nm• 4 individual Nd:YAG lasers

• 4 pulses: time separation = 0-100ms

• 8 ulses: time se aration = 7-145 msPossibility to pump dye lasers and OPO units for tunable radiation

Multiple dye lasers: 20–30 mJ/pulse @ 283nm

One OPO unit: ~10 mJ/pulse @ 283nm

• Wavelengths: 532nm / 266nm

(Thales)


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Different approaches for high speed visualization

• Multi YAG/framing camera approach

Specification- max rep rate: ~200 kHz (8 pulses)

max pulse energy ~400 mJ/pulse @ 532 nm (Thales)

~250 mJ/pulse @ 355 nm~ m pu se nm

Possibility to pump dye lasers and OPO units for tunable radiation

Multiple dye lasers: 20–30 mJ/pulse @ 283nm

ne un : ~ m pu se nm

• kHz laser/CMOS high-speed camera approach

t

- x : ~ z

max pulse energy @ 10 kHz (Edgewave HD40IV-E):

~13 mJ/pulse @ 532 nm

~4 mJ/pulse @ 266 nm Applications: Transient phenomena, e.g;

I nitionPossibility to pump dye laser

~0.3 mJ/pulse @ 283 nm at 10 kHz

Extinction

MisfireFlashback


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Characteristics - kHz Edgewave Nd:YAG


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Characteristics - Sirah credo kHz dye laser

• ar a e wave eng w requency

doubling

• Conversion efficiency of ~40 % atnm o am ne

• Maximum UV (OH) output 3W

(300uJ @ 10kHz)


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Wavelength extension techniques.1. Fre uenc Doublin

• Frequency doubling

1 2 ......

P =

1 E0 exp(- i

t) + 2 E02

exp(- i2

t) + .......• Use doubly-refractive crystal to increase the

efficiency by phase-matching

• requency m x ng r p ng sum erence can a so e

achieved

Characteristics

• Easy to apply• g e c ency

• Scanning not possible if not

•Linewidth increase


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Wavelength extension techniques.

2 Optical parametric oscillator (OPO)

In an OPO, a pump beam

is frequency converted to

two other wavelen ths inVariable angle

a crystal.

The output wavelengths

355

nm

s - nm

(signal)

i 730-2000 nm

depend on the angle of

the crystal.

pPump beam

BBO-crystal

er

tuneable in a large range

of wavelengths.

Pump Signal Idler

nm941 nm

355 nm 400 nm 710 nm 2000 nmWavelength


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Detectors: Photomultiplier

A photomultiplier (PMT) is a sensitive detector, where incidentradiation enters a cathode that strikes out electrons from a

p o oca o e. ey are en acce era e owar s a ser es o

dynodes giving rise to a large number of secondary electrons.

A photomultiplier is often used for time-resolved detection together

with a digital oscilloscope.

Photocathode Dynode

Anode

Incident

light

Focusing electrode Accelerating grid

Per-Erik Bengtsson


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Detectors: Intensified char e cou le device ICCD

-

MCP

Objective

Per-Erik Bengtsson


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CCD- camera chip

The central unit in a CCD-

camera is the CCD-chip.

p xe s ze o aroun

m and a number of pixels

normal.

Per-Erik Bengtsson


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Detectors: Intensified charge couple device, ICCD

An image-intensified

-camera as a mu -

channel plate in front of

the CCD-chip.

CCD-chipThe purpose of this

device is mainl to

Multi-channel

• intensify the signal• work as a time gate

•

-

plate (MCP)

wavelength range

Photocathode Lens couplingsurface

Phosphor

surface

Per-Erik Bengtsson


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Framing camera

us om mo e g spee

camera (Imacon 468, DRSHadland, UK)

1 1 M

i r Beam s litter o tics

• 8 independent CCD’s,

576x384 pixels 10 ns

C C D

m s

p l i t t e r

n a

l i m a g e

t e n s i f i e r

M C

m

e s t o r e

s s

s t o r a g e

n s

m o u n t

C D

2 - 6

o r

• Optional image intensifier

- C C D

8

B e

O p t i i n

M C P 8

F r

M a

Iris

L e

M i r r

o r

resolution


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High speed camera

Photron

Fastcam SA5 Lambert image intensifierHiCATT 25 Gen 2

• 1024*1024 pixels at 7500 fps • Intensifies ~100 000 times

• p o ps a re uce • Gate width down to 3ns


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Some characteristics of CCD-cameras

Dynamic range The number of charges that can be collected

needed for detection above the noise level.

uan um e c ency e e c ency n convers on o p otons tocharges.

Wavelength sensitivity The sensitivity of a CCD-chip to differentwavelengths of incident radiation.

Read-out time The time it takes between two recordings for

a camera.

Binning This means that the charge from several“ ”, . , .

increases sensitivity and decreases readouttime.Per-Erik Bengtsson


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Optics

Polariser Opticalfilters

lens

lenses Prism

Per-Erik Bengtsson


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Overlapping / Separation of beams

• Dichroich mirrors are

used to separate laser

532 nmbeams of different

colours (wavelengths)

from each other.

1064 nm• They can be

532 nm +

1064 nm

reflect and transmitdifferent wavelengths. 630 nm

532 nm +

630 nm

532 nm

Per-Erik Bengtsson


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Interference filter

•

m i s s i o n

Full Width at

Half Maximum

(FWHM)

transmits a wavelength

interval around a centre

T r a n s.

• The transmitted

WavelengthCentre

wave engt nterva s

given as FWHM and isnormally 1, 3 or 10 nm.

wave eng

Interference filter with centre wavelength

of 589.3 nm and with FWHM of 10 nm.

Per-Erik Bengtsson

L fil


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Long-pass filter

-

wavelengths longer than a

specific wavelength. The

transmission is often

specified.

OG 570

GG 495

Per-Erik Bengtsson

Sh t filt


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Short-pass filter

-

wavelengths shorter than a

specific wavelength. The

transmission is often

specified.

SP 560 nm

Per-Erik Bengtsson

Wi d t i l


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Window material

• Spectroscopy is often

applied at

n

wavelengths in the

ultraviolet region


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Prisms

There are different kinds of prisms that can be used for

eren as s.

• to separate different polarisations of the light

• to separate beams of different wavelengths

• o mprove e po ar sa on o a eam

• to reflect a beam 90 degrees

• to reflect a beam 180 de rees as a dela line

Per-Erik Bengtsson


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I i t h


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Imaging spectrograph

Spatially distributed light

on the entrance slit of the

spectrometer

1

2

Spatialinformation

2

3

informationPer-Erik Bengtsson

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Lecture 3 Instrumentation Special