Emily Collier- Shaping Laser Pulses

8/3/2019 Emily Collier- Shaping Laser Pulses

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OutlineOutline

MotivationMotivation

Experimental SetExperimental Set--UpUp Theory behind the setTheory behind the set--upup

ResultsResults

AcknowledgementsAcknowledgements


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MotivationMotivation

Attosecond pulses could be used to studyAttosecond pulses could be used to studytimetime--dependence of atomic dynamics.dependence of atomic dynamics.

Greater control of pulse duration gives aGreater control of pulse duration gives abetter control of the power produced frombetter control of the power produced fromeach pulse as well.each pulse as well.


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The SetThe Set--UpUp

Diffraction Grating Diffraction Grating

ConcaveMirror

Concave

Mirror

BBO CrystalSHGPrism

Direction of grating (235 grooves/mm)

Incoming Pulse

SLM

500 nm

1000 nm

SpectrometerConcavemirror

F=500mm


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AlignmentAlignment

Grating

Green laser

532nm

first orderdiffraction(532nm)

second order

diffraction(1064nm)

64mm


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Make 1 order and 2 order spotsMake 1 order and 2 order spots

overlap on the output gratingoverlap on the output grating

Spots overlap

Use CCD

cameras to

detect the

overlap

Change the inclination

of input grating toadjust vertical position

of two spots on the

output grating.

Adjust the location of

this reflecting mirror tooverlap spots

horizontally.


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TrialsTrials--green laser and spectrometergreen laser and spectrometer


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For SHGFor SHG

Two photonsTwo photons enter the BBO. Eachenter the BBO. Each has a frequencyhas a frequency. One photon leaves the BBO with frequency (2. One photon leaves the BBO with frequency (2).).

The contribution of each initial photonThe contribution of each initial photon 1,1, 22 is as followsis as follows

11 == ++ ;; 22== ; 2; 2== 11 ++ 22WhereWhere is just a way of expressing the energy differenceis just a way of expressing the energy difference

between the contributions of each photonbetween the contributions of each photonThe spectrum of a beam is given byThe spectrum of a beam is given by

2( ) { ( )}S E t[ | F()(2)


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2 3

2 3

2

( ) ( )

( )2 6

( )2 6

2 ( )

N N

N NN N

N NN N

N N

( ; ( ;

dd dddd! ( ; ; ;

dd dddd ( ; ; ;

dd! ( ;

2( 2) (2 ) ( ) ( ) exp{ [ ( ) ( )]}S E E i d N N( w! ( ; ( ; v ( ; ( ; ;

MIIPS (Multiphoton Intrapulse Interference Phase Scan)MIIPS (Multiphoton Intrapulse Interference Phase Scan)

Let frequency= ; difference= ; parameters=, ; phase= ;

phase correction = f

Take a Taylor approximation

And

You get


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Let frequencyLet frequency== ; difference; difference== ; parameters; parameters==,, ; phase; phase== ;;

phase correctionphase correction == ff

A maximum SHG signal corresponds to flat phase. If we can modulate

some phase make set ,, and scan

( ) cos( )f E K H( ! ( 2( ) cos( )f EK K Hdd( ! (

( ) ( )fNdd dd( ! (

0( ) 0Nd( !

0( )0

N ( !

( )N (

0f Ndd dd !


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Data obtained using the 10%Data obtained using the 10%

beambeam


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Amplitude


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Fourier TransformFourier Transform

By performing anBy performing aninverse Fourierinverse Fourier

transform we cantransform we canchange thechange theinformation from ainformation from agraph showinggraph showing

frequencyfrequency to ato agraph showing time t.graph showing time t.

1( ) ( ) exp( )2

f t F i t d [ [ [T

g

g

!


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Intensity (counts)


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20

2

1( ) [ 2( ) ]

2

2 ln(2)

1.17741

1.17741 32.24545

37.9661 fs

x xf x

WW

FWHM W

W

T

!

!

}

! v

!

Original Phase

Flat Phase


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The FullThe Full--WidthWidth--

HalfHalf--MaximumMaximum

FullFull--widthwidth--halfhalf--maximummaximum is the distanceis the distancebetween the halfbetween the half--maximummaximum

points.points.

Also: we can define these widths in terms off(t) orof its intensity, |f(t)|2.

Define spectralwidths (([) similarly in the frequency domain (tp[).

t

(tFWHM

1

0.5


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With some small phase correctionsWith some small phase corrections

The last weeks workThe last weeks work


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MIIPS after 9 phase correctionMIIPS after 9 phase correction

attemptsattempts


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ComparisonComparison


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AcknowledgementsAcknowledgementsandand

CitationsCitations Professor Zenghu ChangProfessor Zenghu Chang

He Wang, Yi WuHe Wang, Yi Wu

Dr.Larry Weaver

Dr.Larry Weaver

Dr. Kristan CorwinDr. Kristan Corwin

Kansas State UniversityKansas State University

Trebino, Rick. "FROG:Lecture Files."Trebino, Rick. "FROG:Lecture Files." Georgia Institute ofGeorgia Institute ofTechnology School of PhysicsTechnology School of Physics. Georgia Tech Phys Dept.. Georgia Tech Phys Dept.

29 Jul 200729 Jul 2007..

Lozovoy, Vadim. "Multiphoton Intrapulse Interference."Lozovoy, Vadim. "Multiphoton Intrapulse Interference."Optics LettersOptics Letters 29.7(2004): 77529.7(2004): 775--777.777.


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SLM

Grating Grating

ConcaveMirror

ConcaveMirror

f=500mm

Supplementary and extendedSupplementary and extended

materialmaterial

QQ

QQQ

QQQ

45.492/)90(

/])/(sin[arctan

169.9748.6421.3

842

.6

748.6

59.13

}!

!

!!!!

FK

PF

FE

afx

D

64mmX5mm

X


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BBO (BBO (-- Barium Borate) CrystalBarium Borate) Crystal

Why is the BBO crystal used??Why is the BBO crystal used??

Used to separate the beam into itsUsed to separate the beam into its

fundamental and second harmonicfundamental and second harmonicfrequenciesfrequencies


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For SHGFor SHG

Two photonsTwo photons enter the BBO. Eachenter the BBO. Each has a frequencyhas a frequency. One photon leaves the BBO with frequency (2. One photon leaves the BBO with frequency (2).).

The contribution of each initial photonThe contribution of each initial photon 1,1, 22 is as followsis as follows

11

== ++ ;; 22

== ; 2; 2== 11

++ 22WhereWhere is just a way of expressing the differenceis just a way of expressing the difference

between the contributions of each photonbetween the contributions of each photon

The spectrum of a beam is given byThe spectrum of a beam is given by

The spectrum of the beam is given by SThe spectrum of the beam is given by S22 of 2of 2 isis2

(2)(2 ) ( ) ( ) exp{ [ ( ) ( )]}S E E i dN N( w! ( ; ( ; v ( ; ( ; ;

2

( ) { ( )}S E t[ | F()(2)


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( ) cos( )f E K H( ! (

Maximum SHG signal correspond to flat phase. If we can modulate some

phase make set ,, and scan

2

( ) cos( )f EK K Hdd( ! (

( ) ( )fN dd dd( ! (

0( ) 0Nd( !

0( ) 0N ( !

( )N (

0f Ndd dd !

2 3

2 3

2

( ) ( )

( ) 2 6

( )2 6

2 ( )

N N

N NN N

N NN N

N N

( ; ( ;

dd dddd! ( ; ; ;

dd dddd ( ; ; ;

dd! ( ;

2( 2) (2 ) ( ) ( ) exp{ [ ( ) ( )]}S E E i d N N( w! ( ; ( ; v ( ; ( ; ;

We used MIIPS (Multiphoton Intrapulse Interference Phase Scan) to get aWe used MIIPS (Multiphoton Intrapulse Interference Phase Scan) to get apicture of the phase of each wavelength contained in the pulsepicture of the phase of each wavelength contained in the pulse

Let frequency= difference= parameters=, phase= phase correction =f


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Project GoalsProject GoalsDuring the summer of 2007, I spent approximately ten weeks studying andDuring the summer of 2007, I spent approximately ten weeks studying andresearching at Kansas State University Physics Department. My projectresearching at Kansas State University Physics Department. My project

during this time was to work with two graduate students to shape laserduring this time was to work with two graduate students to shape laserpulses. Specifically, we designed and set up a system that (hopefully)pulses. Specifically, we designed and set up a system that (hopefully)

allows us to adjust the phase of each separate frequency of a laser lightallows us to adjust the phase of each separate frequency of a laser lightpulse. Using a device called an SLM, Spatial Light Modifier, we were able topulse. Using a device called an SLM, Spatial Light Modifier, we were able toapply different voltages to each pixel on a liquid crystal screen. Each pixelapply different voltages to each pixel on a liquid crystal screen. Each pixelcorresponds to a different frequency of light. When we apply the differentcorresponds to a different frequency of light. When we apply the differentvoltages, we change the phase of each frequency, our goal is to make thevoltages, we change the phase of each frequency, our goal is to make thephase of each frequency the same. Then applying a Fourier Transform wephase of each frequency the same. Then applying a Fourier Transform wewere able to see how this phase shift changed the timewere able to see how this phase shift changed the time--dependence of thedependence of thepulse. Our goal is to be able to control the pulse as we choose, thus makingpulse. Our goal is to be able to control the pulse as we choose, thus making

it possible to control the duration of each pulse. We are hoping to attainit possible to control the duration of each pulse. We are hoping to attainattosecond pulses through this method.attosecond pulses through this method.

As a part of this research, I was also given the opportunity to learn manyAs a part of this research, I was also given the opportunity to learn manydifferent styles of programming, including, C, C++ ,and LabView. To many,different styles of programming, including, C, C++ ,and LabView. To many,these programs might seem basic, but I had not yet encountered them inthese programs might seem basic, but I had not yet encountered them inmy normal studies, so this presented a new and interesting challenge formy normal studies, so this presented a new and interesting challenge forme. LabView especially proved to be quite the ordeal and I spent a goodme. LabView especially proved to be quite the ordeal and I spent a gooddeal of time learning this program and attempting to write a program thatdeal of time learning this program and attempting to write a program that

would be useful to our experiment with it.would be useful to our experiment with it.

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Emily Collier- Shaping Laser Pulses