Heterodyne Detected Sum Frequency Generation (HD-SFG) Igor Stiopkin, Igor Stiopkin, Himali Jayathilake, and Alexander Benderskii Department of Chemistry Wayne State University Detroit, MI

Vibrational Sum Frequency Generation  (2) RES ijk = N s  T i T j  T k  , ,    (2) (  ) E i (  SFG )   (2) ijk (  1,  2 ) E j (  1 )E k (  2 )  s (2) E(2)E(2) E SFG (  1 +  2 ) E(1)E(1)  IR  vis  SFG |v=0  |v=1  Surface Coverage SFG Signals are Weak (x ) Phase is Unknown  TOTAL (2) =  RES (2) +  NR (2) → φ RES-NR

Homodyne-Detected SFG VIS. IR SFG Monochromator SFG Intensity Is Measured Broad Band SFG Setup CH region of 1-octanol van der Ham, Vrehen, Eliel, 1996 Richter; Petralli-Mallow; Stephenson, 1998 Hommel; Ma; Allen, 2001 CH 3 SS CH 3 FR air/water Homodyne SFG works at High Signals / Coverages CH 3 SS CH 3 FR 1-octanol : air/water

Heterodyne vs. Homodyne SFG VIS IR Heterodyne SFG is Sensitive to Adsorbant at Low Coverage Heterodyne SFG Contains Phase Information LO SFG

Experimental Broad-Band SI HD-SFG Setup Phase is Locked Across the Spectrum SFG Spectrum, Phase, and Temporal Profile Recovered vis Monochromator IR Sample CCD LO SFG LO KNbO 3 ω Time Domain Frequency Domain Spectral Interferometry

Experimental Spectral Interferograms

Data Analysis IFFT FFT (a) (b)(c)(d) Real Part Amplitude Filtering Does not Affect SFG Signals SIFID Filtered SI HD-SFG

Spectrum Renormalization (a) (b) (c) Gold Measured Recovered from HD-SFG HD-SFG f(ω)f(ω)Homodyne Apparatus Function f(ω) Reflects LO Spectrum and Interference Quality

Background Phasing (c) Phasing (a) (b) N=0% N=10% Nonresonant part of SFG is used for Phasing Resonant part Nonresonant part

Background Subtraction - = (a) (b)(c) Analyte SFG Background SFG Measured HD-SFG N=10% N=0% HD-SFG Recovers Analyte Contribution

SFG Spectrum Recovery SFG vis IR LO HD-SFG Recovers Spectra Below Neat Interface Background 100% 80% 60% 40% 25% 10% Measured Homodyne Analyte SFG ×3×3 ×3×3 ×3×3 ×3×3 8% 6% 3% 6%

SFG Temporal Profile Recovery Res. &NR Res. Concentration Dependence of Temporal HD-SFG Resonant HD-SFG ~N Homodyne SFG ~N 2 HD-SFG Recovers SFG Spectra at few % monolayer level

Conclusions 1.HD-SFG Recovers SFG Spectra at few % monolayer level 2.HD-SFG allows to measure phase and subtract NR background 3.HD-SFG scales linearly with surface coverage 4.HD-SFG Recovers temporal profiles (FID) 6% c

Acknowledgments Advisor: Alexander Benderskii Postdocs: Andrey Bordenyuk Graduate students: Himali Jayathilake Champika Weeraman Achani Yatawara Fadel Shalhout Undergrads:Adib Samin WSU start-up grant WSU research grant NSF CAREER Grant No Funding

Sample: 1-Octanol at Air/Water Interface CH 3 (CH 2 ) 6 CHOH Fixed Total Bulk Octanol Concentration (C=1mM) CH 3 (CH 2 ) 6 CHOH / CD 3 (CD 2 ) 6 CDOH Molecular Orientations Preserved for all N Ref.