Development of a HighSensitivity Pump-Probe Fast
Scanning Delay Line
Stephanie Majewski
University of Illinois @ Urbana-Champaign
University of Florida
Faculty Mentor: Professor David Reitze
Introduction
• Femtosecond “LASER”s
• Pump-Probe Spectroscopy
• Lock-in Method
• Fast-Scan System
Femtosecond Lasers
Conventional Laser
continuous
Femtosecond Laser
1 fs = 0.000 000 000 000 001 s
What Happens in
100 Femtoseconds?
• Light Travels 30 μm
• Electrons Collide With Electrons
• Solids Begin to Melt Under Laser Irradiation
• Chemicals Dissociate
There are about as many femtoseconds in a minute
as there are minutes in the age of the universe.
Shaker
Pump
Reference
Beam Splitter
Laser
Beam Splitter
Photo
Diode
M
Lens
Sam ple
Probe
Project Objectives
• Characterize Motion of Shaker
• Design Mirror Mount
• Optimize Performance of ShakerMount System
• Implement System in Pump-Probe
Experiment
The
“Shaker”
k
0 
m
M1
Shaker
He Ne
M2
M3
Diverging
Lens
Converging
Lens
Photo diode
Signal
Generator
Oscilloscope
Ch1
Ext Trig
Major axis amplitude vs frequency of oscillation
6
Load
0.00g
1.85g
2.34g
3.03g
3.52g
4.21g
4.70g
5.88g
7.06g
7.63g
8.81g
9.99g
10.51g
11.69g
Mirror Mount
5
Amplitude (mm)
4
3
2
1
0
20
30
40
50
60
Frequency (Hz)
70
80
90
100
Major axis amplitude and time delay vs load
4.5
30
Frequency (Hz)
60
65
70
75
80
85
90
Amplitude (mm)
3.5
3.0
25
20
2.5
15
2.0
1.5
10
1.0
5
0.5
0.0
0
0
2
4
6
Load (g)
8
10
12
Time Delay (ps)
4.0
FIG. 6 Mirror Mount
Mirror Mount
Mirror Diameter: 6mm
Obstacles ...
• Elliptical Beam
Shape
• Unstable Mirror
Mount
• Wobble in Drive
Arm of Shaker
Solutions!
• Uniform Bolt Force on Mirror
Yielded Circular Beam Shape,
Mirror Rattle Minimized
• Extra Screw Added Stability
to Mount
• Beam Jitter Corrected Optically
FIG. 8 Beam wobble characterization setup
Signal
Generator
M1
HeNe
Converging
Lens
M2
Iris
m
M3
Shaker
Oscilloscope
Optical Position
Sensor
Tetra-Lateral
Detector
Beam Jitter amplitude vs frequency
Beam Jitter Amplitude (mm)
5
Before
4
3
2
1
0
40
50
60
70
Frequency (Hz)
80
90
100
Beam Jitter amplitude vs frequency
Beam Jitter Amplitude (mm)
5
Before
After
4
3
2
1
0
40
50
60
70
Frequency (Hz)
80
90
100
Time-Resolved Nanotube
Transmission Measurement
• Achieved successful fast-scan system
implementation in pump-probe experiment
• Measurement itself unsuccessful due to
intrinsic scattering of sample
• In future, can try using cross-polarization
and other methods to reduce scattering.
Conclusion
• Developed Shaker Design for Fast Scanning
System
• Characterized Shaker Motion and Corrected
Beam Jitter to Within Acceptable Limits
• Implemented Shaker in Time-Resolved Carbon
Nanotube Transmission Measurement
Acknowledgements
Professor David Reitze
Mark Moores and Anatoly Efimov
Drs. Kevin Ingersent and Alan Dorsey
NSF Research Experience for Undergraduates