1. Automated 2D IR Spectroscopy using a high repetition rate laser system
and mid IR pulse shaper
Sudipta Mukherjee
Zanni Group
Department of Chemistry
University of Wisconsin at Madison

2. 2D IR Spectroscopy-The vibrational analogue of 2D NMR
Merits of 2D IR Spectroscopy
Molecular Structures-Vibrational frequency ,coupling, anharmonicity, transition dipole angles
Ultrafast Dynamics-fast time resolution(fs/ps)
Environment-Lineshape analysis
Scientific Problems
Characterization of Transmembrane Proteins eg CD3ξ(receptor in T cells)
,Ovispirin(antibiotic polypeptide),M2(ion channel)etc
Studying folding kinetics eg HIAPP(HUMAN ISLET AMYLOID POLYPEPTIDE)

3. Examples of FTIR and 2D IR spectra of HIAPP
HIAPP-Human Islet Amyloid Polypeptide-Type 2 diabetes

4. Traditional ways of doing 2D IR spectroscopy
Hole Burning Method
Easier
time resolution –less
Pulsed Photon Echo Method
Difficult
Better time resolution

5. Regenerative Amplifier
Our Experiment set-up: automatic 2D IR spectrometer
Nd:YVO4
CW laser
Ti:Sapphire
Oscillator
Stretcher
Regenerative Amplifier
Compressor
Nd:YLF
ns laser
b-BBO based
OPA
Difference
Frequency
Mixing
w/ AgGaS2
800 nm, 88 MHz. 2 nJ/pulse
idler
Ge AOM
Pulse
Shaper
Tunable mid-IR
3-10 mm, 2-5 mJ/pulse
800 nm, 1kHz, 1mJ/pulse
signal
beam dump
optical chopper k1
kpump-probe= k1+k1+k2 t
sample
k1+k1 k2
monochromator
MCT array - +

6. How to generate the double pulses-pulse shaper
Ge-AOM is used as a modulated grating
Phase and amplitude tailored by a 75 Mhz acoustic wave of bandwidth 50 Mhz

7. Advantages of the pulse shaping method
Easier alignment.
Little maintenance.
Fast data collection.
Absorptive spectra-no phasing needed!
Complicated pulse shapes, higher
dimension.

8. However….

9. Moving towards even faster data collection
30 Khz laser!!
A complete laser system including oscillator, cryo cooled amplifier and pump lasers-KM LABS
Rep Rate:50 KHz
Pulse Duration:40 fs(expected)
Pulse Energy: uJ
Cryo-cooling and Downchirped Pulse Amplification gives high rep rate with
not much loss of power.
Moving towards even faster data collection
More averaging over larger number of laser shots.S/N almost 6 times
Even faster data collection-0.3 s
Even lower sample concentration to mimic physiological conditions.

10. Summary: Hence programmable pulse generation in MID IR achieved.
Easier implementation of 2D IR spectroscopy.
We expect to get even better structural resolution with our new laser system.
Understand the role of intermediates in HIAPP folding.

11. Thanks for your attention!
Acknowledgement
Dr Martin Zanni
Sang-Hee Shim
Dave Strasfeld
Ann Woys
Wei Xiong
Emily Blanco
Yun Ling
Dr Chris Middleton
Dr Prabudhdha Mukherjee
Thanks for your attention!