Lecture 3 Instrumentation Special
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Transcript of 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
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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.
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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
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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
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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
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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
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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