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Kansas Light Source
Upgrade
Scott Palmiter
Mentor: Dr. Zenghu Chang
Lab Partner: Jason Tackett
Kansas Light Source
• What is the KLS?
– Ultrafast High Intensity Laser Facility
– Provides very short pulses
» Pulse Duration: 25fs
» On the order of molecular oscillations
– Wavelength: 790nm (Infrared)
– Pulse Energy: 2.5mJ
– Used for “studying the fastest dynamics in
atoms, molecules and other matter under the
influence of strong electric fields.”
Kansas Light Source
• How does the KLS work?
– Seed pulses with 1nJ at
10fs are stretched to 100ps
– Avoids damage to amplifying
crystal
– With each successive pass
through the crystal, the
beam gains energy up to
2.5mJ
– 14 total passes
– Amplified beam is
compressed to 25fs
Kansas Light Source
• Sample setup
Pulse Source
Stretcher
Amplifier
Final Beam
Gratings
Compressor
Kansas Light Source
How does the 790nm beam gain energy?
– The pump laser excites the atoms in the
Ti:Sapphire crystal to a higher excited state
creating a population inversion
– As the infrared beam passes through the
media, it stimulates the atoms and lowers their
energy states. As the atoms change energy
states, photons are ejected and picked up by
the passing beam
Kansas Light Source
• How does the 790nm beam gain energy?
– Each pass has more photons, and
subsequently causes the ejection of more
photons, amplifying the beam
Kansas Light Source
• What are gratings?
KLS Upgrade
M6
M4
Ion
Pump
L3
L6
M2
M3
L2
L1
M5
BS1
Legend:
M – Mirror
L – Lens
BS – Beam Splitter
M1
L4
L5
Darwin 527 nm
Pump Laser
KLS Upgrade
1mm spot size
Pump Beam
25.4mm
Crystal
Diverging
Lens
Collimating
Lens
Converging
Lens
KLS Upgrade
M12
M11
RM1
M13
PM1
PM2
RM2
M6
RM4
M4
Ion
Pump
M7
L3
L6
Pockel’s
Cell
RM3
Telescope
M2
M3
L2
L1
M10
From Amplifier 1
M5
BS1
L4
L5
P2
Final Beam
Legend:
M – Mirror
L – Lens
RM – Retro Mirror
PM – Pump Mirror
G2
P1
Compressor
M8
G1
M9
M1
Darwin 527 nm
Pump Laser
Pump Laser System
• Began building the
M4
lens-mirror system to
L3
achieve 1mm spot
size at future location
M3
of crystal.
L2
L1
• Practiced enlarging,
collimating, and
converging to desired
size.
• Learned convention
Ion
of measuring spot
Pump
size.
M6
L6
M2
M5
BS1
M1
L4
L5
Darwin 527 nm
Pump Laser
Pump Laser System
• Disaster: Pump Laser broke down
• Delay: Next week
• More Problems:
– Sapphire Crystal cut wrong
• Delay: End of August
– Ion pump not manufactured yet
• Delay: End of August
– Manufacturing problems with pump mirrors and retro
mirrors, telescope mirrors
• Everything but one telescope lens has arrived, end of Aug.
Compressor Construction
• Major components:
– Gratings
– Periscopes
Final Beam
• Steps to complete:
– Align components
– Use uncompressed
beam to optimize and
test
– Use the FROG to
estimate resulting
pulse width
P2
G2
P1
WP
G1
M9
Legend:
M – Mirror
P – Periscope
G – Grating
WP – Half wave plate
Amplified Beam
Compressor Construction
Grating Alignment Criteria: grooves must be
perpendicular to the table
Mirrors
= Iris
Same height
for alignment
Laser
Grating
Compressor Construction
Periscope Alignment Criteria: beam entering
parallel, exits parallel
Compressor Construction
VND
Final Beam CCD CAM
Beam Height = 5”
Gratings
Periscope
Beam
BeamHeight
Height=≈5”
3.85”
Periscope
Compressor Construction
Checking Polarization
– Must make sure polarization of incident beam
on the gratings is correct
– Check by finding the setting on half wave
plate that would give us maximum intensity
– Easiest with zero order
Compressor Construction
Optimizing 2nd order dispersion:
– Finding correct distance between gratings
– Using a very small focal length lens (30mm),
white light is generated and the oscillations in
the in the air caused by the laser create noise
– Find the brightest light and loudest noise level
Compressor Construction
Optimizing 2nd order dispersion:
P2
G2
P1
G1
Point of white
light and noise
M9
Compressor Construction
Optimizing 3rd order dispersion:
– Checking parallelism between the gratings
– The spectrum of the compressed beam
should be circular
P2
G2
P1
G1
M9
Compressor Construction
Spectra of Amplified Beam Before and After
Compression
1.2
1
Intensity
0.8
0.6
After
Before
0.4
0.2
0
-0.2700
750
800
Wavelength (nm)
850
900
Compressor Construction
FROG (Frequency Resolved Optical Gating)
Resulting estimations:
Estimation:
Pulse Width: 29.91 fs
– Gives a 2D array combining information of time and
Spectral Width: 44.84nm
wavelength called a spectrograph
t
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THANK YOU!!
• Dr. Chang, Dr. Weaver, Dr. Corwin
• SUROP – Dr. Shanklin, Amelia Asperin
• KLS Group
Sources
Diffraction Gratings Brochure. Optometrics Corporation. 28 July 2006.
PDF File. <http://www.optometrics.com/prod/spectro/gratings/
gratingbrochure.pdf>
Kansas Light Source. 10 February 2006. Kansas State University. 23
July 2006. <http://jrm.phys.ksu.edu/lasers .html>.
Paschotta, Dr. Rüdiger. Chirped Pulse Amplification. 06 June 2006. RP
Photonics Consulting. 23 July 2006. <http://www.rp-photonics.com
/chirped_pulse_amplification.html>.
Pulse Compression Gratings. Newport Corporation. 23 July 2006.
<http://www.newport.com/store/genproduct.aspx? lone=DiffractionGratings&id=5271&lang=1033>.
Siegman, Anthony E. Lasers. University Science Books. Sausalito,
California: 1986.
Kansas Light Source
Methods of measuring spot size
View of CCD
Known
distance
– Create a ratio of length to pixels.
– Multiply be number of pixels the beam takes up.
– Ratio changes every time the CCD is moved
Kansas Light Source
Methods of measuring spot size
– Create ratio, it remains constant
– Ratio : 0.01195 mm/pixel
CCD Cam Screen
492 pixels
510 pixels
Compressor Construction
Spectrum Before Compression
1200
Intensity
1000
800
600
400
200
0
-200700
750
800
Wavelength (nm)
850
900
Compressor Construction
Spectrum After Compression
300
250
Intensity
200
150
100
50
0
-50700
750
800
Wavelength (nm)
850
900