Spectroscopic Line Shapes Of Broad Band Sum Frequency

Spectroscopic Line Shapes Of Broad Band Sum Frequency Generation Himali Jayathilake Igor Stiopkin, Champika Weeraman, Achani Yatawara and Alexander Benderskii Department of Chemistry, Wayne State University Detroit, MI

Interfacial Studies Nature • Biological Processes • Molecular Electronics • Nanotechnology Living Organisms Molecular Organization at the Surface (Cell membrane) Function Industry (LCD Displays) Surface Selective Spectroscopy

Outline Amplitude Spectroscopic Signal Frequency Spectroscopic Line Shapes 1. Amplitude 2. 2. Line Width 3. 3. Transition frequency Information extracted from Line shapes 1. Molecular organization 2. i. Orientation 3. ii. Conformational order 4. iii. Packing 5. 2. Molecular Dynamics

Surface-Selective Non-Linear Optical Spectroscopy Second Order Nonlinear Susceptibility Polarization Surface selectivity: (2) = 0 in isotropic media (bulk)

Vibrational Sum Frequency Generation (SFG) Broad-Band Vibrational SFG (Broad-band IR pulse + Spectrally narrow vis pulse) vis SFG vis SFG= IR+ vis IR |v=1 IR |v=0 van der Ham, Vrehen, Eliel Opt. Lett. 21, 1448 (1996) Richter; Petralli-Mallow; Stephenson, Opt. Lett. 23, 1594 (1998) IR SFG

Experimental Set-up 800 nm 40 nm bandwidth Shaped vis pulse 1. i. Stretcher 2. ii. Etalon vis 2 Pump Lasers CCD Monochromator Oscillator 1 G SF Amplifier OPA 803 nm 26 nm bandwidth 40 fs 2 m. J/pulse, 1 k. Hz IR output: 3 -8 m 65 -75 fs 300 cm-1 bandwidth 1 -2 J/pulse Sample IR SFG Spectrum

Stretcher and Etalon Tunable slit OPA Etalon Grating To the sample

Spectroscopic Line Shapes in SFG Peaks are asymmetric-interference of the resonant and the nonresonant SFG Peaks are broad-convolution of the molecular response with the visible up-converted pulse Propiolic acid At air- water interface

How Time Delay Affects SFG Spectra? (-) ve Time Delay (+) ve Time Delay

1. Stretcher Based Visible Pulses Vis. Width=37 cm-1 Vis. Width=17 cm-1 Electric field of time domain visible pulse

SFG Spectra From Stretcher Based Visible Vis. Width=17 cm-1 Vis. Width=37 cm-1

Fitting Procedure Fourier Transform Time domain Molecular response function Frequency domain 2 nd order susceptibility The 1 st order polarization The BB-SFG Spectrum The 2 nd order polarization FFT

Analysis v. Peak Intensity get maximized at negative time delays 2 Г v. FWHM get minimized at negative time delays

2. Etalon Based Visible Pulse Electric field of time domain visible pulse

SFG Spectra From Etalon Based Visible

Fitting Results

Summary ØVisible pulse shape and time delay can be used to enhance the SFG signal intensity and obtain the desired line shape without sacrificing the spectral resolution Ø Combining theoretical modeling with experimental measurements, measurements i. information such as true line width can be extracted ii. observed line shapes can be described

Acknowledgements The Group Adib J. Samin Funding Wayne State University ACS-PRF NSF http: //chem. wayne. edu/benderskii-group/

Modeled homodyne detected SFG spectrum Asymmetric homodyne detected SFG spectrum Symmetric real part of the resonant contribution Asymmetric imaginary part of the resonant contribution Non-resonant contribution

Visible Pulse Shape From Stretcher The inset shows the front view of the grating

Stretcher and Etalon Tunable slit OPA Etalon Grating To the sample