Probing Molecular Dynamics with Non-Linear Optical Techniques

Probing Molecular Dynamics with Non-linear Optical Techniques by Rune Lausten A thesis submitted to the Department of Physics, Engineering Physics and Astronomy in conformity with the requirements for the degree of Doctor of Philosophy Queen’s University Kingston, Ontario, Canada August 2011 Copyright c Rune Lausten, 2011 Abstract The dynamics of molecules in the gas and liquid phase is investigated using ultrafast optical techniques. The development of sub-25 fs ultrafast sources using noncollinear optical parametric amplification is discussed. These intense pulses are utilized in coherent anti-Stokes Raman scattering to investigate vibrational motion in I2 Br2 and IBr. For larger bio-molecules relevant dynamics may not be related to the absorption of light. Here, a new technique is introduced, in which an optically excitable molecule is incorporated into the bio-molecule. Photoisomerization of the trigger molecule initiates structural rearrangement in the larger system. To demonstrate this approach, azobenzene was synthesized into short strands of DNA to time-resolve base pair destacking dynamics and DNA melting. The isomerization of azobenzene in thin polymer films (and their corresponding change in optical properties) was also used to write birefringence and surface relief gratings. This method was used to demonstrate a rewritable Bragg filter for telecom wavelengths. Lastly, an alternative to typical crystal based wavemixing is presented for the generation of ultrafast tunable ultraviolet and deep ultraviolet pulses. The approach utilizes difference frequency four wave mixing in hollow waveguides filled with noble gas. i Figure 1: The top picture shows an example of non-resonant Coherent Anti-Stokes Raman Scattering, or CARS, formed when three 25 fs laser pulses are overlapped in a microscope cover-slide. In the middle and bottom pictures, either one of the pump beams or the Stokes beam was blocked. This pattern is a result of cascaded third order processes. ii Acknowledgements First I would like to thank my PhD supervisor, Dr. Albert Stolow for making the work presented in this thesis possible. Throughout my degree he has always been insightful and very supportive. His guidance has allowed me to develop both academically and personally, and while the path may not always have been the most direct, it was often the detours that taught me the most. I would like to thank my co-supervisor, Dr. James M. Fraser for help, support and guidance from afar. I thank my supervisor committee, Dr. Marc Dignam, Dr. Kevin Robbie and Dr. Jun Gao for their roles in helping me complete my degree. I would also like to thank my collaborators in the various projects. For the time resolved four-wave-mixing experiments, I would like to thank Dr. Torsten Siebert for kick-starting the project, which later led to interesting results, and discussions with Dr. Olga Smirnova, Stefanie Gräfe and Anders S. Mouritzen. The azo-DNA work was initiated in collaboration with Dr. John Pezacki and his PhD student Bojana Rakic, and later joined by Dr. Helmut Satzger. The experiments on the rewritable azo-polymer surface relief gratings were done in collaboration with Dr. Paul Rochon at the Royal Military College (RMC), and Dr. Pavel Cheben at Institute for Microstructural Sciences (IMS), NRC. Many thanks go to Dr. Ben Sussman for proofreading this manuscript. I would iii also like to thank my friends and co-workers for making my time at the NRC and in Canada so enjoyable. I regret not being able to mention everyone here, but spe- cial thanks go to my wolfpack Anthony Lee, Bojana Rakic, Ben Sussman, Jérôme Levesque and Adrian Pegoraro. Over the years I have also enjoyed the company of Oliver Geßner, Helmut Satzger and Jochen Mikosch both in the lab and outside. None of the work would have been possible without the continuing support of my family and friends. iv Table of Contents Abstract i Acknowledgements iii Table of Contents v List of Tables viii List of Figures ix Acronyms xv List of Publications xvii Chapter1: Introduction .......................... 1 1.1 ThesisOutline............................... 4 1.2 FemtosecondTechnology . 6 1.3 PropagationofUltrashortPulses . 26 1.4 NonlinearOptics ............................. 42 Chapter 2: Time-Resolved Femtosecond Four-Wave Mixing . 53 2.1 Introduction................................ 54 v 2.2 Time-Resolved Frequency Integrated CARS Signal . ..... 60 2.3 Experimental ............................... 63 2.4 ResultsandDiscussion .......................... 67 2.5 Conclusion................................. 84 Chapter 3: Ultrafast Transient Absorption . 87 3.1 Introduction................................ 87 3.2 Transient Absorption Spectrometer Setup . ... 89 3.3 Aligning Procedure for Long Delay Scans . .. 92 3.4 Transient Absorption Experiment on a-AB in DMSO . .. 94 3.5 DataCorrectionandFitting . 97 Chapter 4: Photo Triggered Melting of DNA . 101 4.1 Introduction................................ 101 4.2 The Trigger Molecule and Incorporating it into DNA . .... 103 4.3 SteadyStateResults ........................... 105 4.4 Transient Absorption Experiments: 450 nm Pump-White Light Probe 112 4.5 MD Simulation Results for Single Strand azo-Oligo . ..... 117 4.6 Transient Absorption Experiments: 450 nm Pump-260 nm Probe . 126 4.7 Results................................... 127 4.8 Conclusion................................. 127 Chapter 5: Generation of Femtosecond DUV Pulses in HWG . 130 5.1 Introduction................................ 131 5.2 HollowWaveGuides ........................... 133 5.3 Mode Coupling for Hollow Wave Guides . 135 vi 5.4 Phase-Matching in Hollow Waveguides . 139 5.5 Experimental Setup for Third Harmonic Generation . ..... 141 5.6 Compressing and Characterization using a Two-Photon Autocorrelator 146 5.7 Fifth Harmonic Generation, Towards Tunable VUV . ... 148 5.8 FuturePerspectiveandIdeas. 157 Chapter 6: Rewritable Azopolymer Gratings . 159 6.1 Introduction................................ 159 6.2 Azobenzene Based Polymer Gratings . 160 Chapter7: Conclusion ........................... 169 Appendix A: An Analytical Model for CARS . 172 Appendix B: Experimental Tricks . 179 Bibliography ................................. 181 vii List of Tables Table 4.1 Important dihedral angle values for the cis isomer of azobenzene. 117 Table 4.2 This table contains a subset of force constants chosen to at- tempt the trans to cis isomerization in azobenzene. All values are in kcal/mol. ................................ 117 Table 5.1 Summary of experimental and theoretical conditions for the hollow waveguide generation of third harmonic. 158 viii List of Figures Figure 1 Non-resonant CARS in a microscope coverslide . ii Figure1.1 ATi:sapphireoscillator. .. 7 Figure1.2 Chirpedpulses .......................... 8 Figure1.3 Sketchofagratingstretcher . .. 10 Figure 1.4 Sketch of a regenerative amplifier . ... 12 Figure 1.5 Sketch of the layout of a folded grating compressor ...... 13 Figure 1.6 Conditions for parametric amplification . ...... 14 Figure1.7 wavevectordiagramfortheNOPA . 14 Figure 1.8 Phase matching curves for a 400 nm pumped NOPA . 17 Figure 1.9 Phase matching curves for a 267 nm pumped NOPA . 18 Figure 1.10 Sketch of the layout of a typical 400 nm pumped two stage NOPA 19 Figure 1.11 Scanning background free intensity autocorrelator....... 21 Figure 1.12 Noncollinear intensity autocorrelation trace and the interfero- metric intensity autocorrelation traces . 24 Figure 1.13 A typical two prism sequence used in a prism based compressor 28 Figure 1.14 Beam passage through the two prisms of a prism compressor . 29 Figure 1.15 Details of the beam passage through the second prism..... 30 Figure 1.16 Calculated GVD (left) and TOD (right) for different materials 32 ix Figure 1.17 Ratio between GVD and TOD for different optical materials . 33 Figure 1.18 Stretching of a 200 nm, 30 fs pulse by 3.2 mm CaF2 ...... 35 Figure 1.19 Phase contribution from a FS or CaF2 based prism compressor 36 Figure 1.20 A sketch of the two parallel gratings in a grating compressor . 38 Figure 1.21 Stretching of a 200 nm, 10 fs transform limited pulse by 3mm CaF2 ................................... 39 Figure 1.22 Phase contribution of a CaF2 prism compressor optimized for 200nm,10fspulses .......................... 40 Figure 1.23 Phase contribution of a grating compressor, set up to compress 200nm,10fspulses .......................... 40 Figure 1.24 Resonance structure for the third-order nonlinear susceptibility 49 Figure 1.25 Double sided Feynman diagrams . .. 49 Figure 1.26 Energy diagrams for the resonant and non-resonant contribu- tionstoCARS ............................. 51 Figure 2.1 Energy level diagrams for vibrationally resonantCARS .... 57 Figure 2.2 Pulse and level scheme for the time resolved CARS . ..... 58 Figure 2.3 Calculated CARS signal for wavepacket dynamics in the I2 B-state 62 Figure 2.4 Fourier transform of the calculated CARS signal . ....... 62 Figure 2.5 Dispersion-free, polarization maintaining, time- and frequency- resolvedCARSspectrometer. 65 Figure 2.6 Time- and frequency-resolved fs CARS spectrum of iodine . 68 Figure2.7 A cut of the CARS data at λaS=520nm ............ 69 Figure 2.8 Fourier transform power spectra of the iodine transient . 70 x Figure 2.9 cuts of the time- and frequency-resolved femtosecond iodine CARSdata ............................... 71 Figure 2.10 Fourier transform power spectra of the iodine transients . 73 Figure 2.11 Log spectrogram of the CARS signal detected at 520nm ... 75

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