Femtosecond nonlinear optics in optical parametric amplification and pulse-shaping phenomena of semiconductors

This thesis presents investigations of nonlinear optical interaction between femtoseond laser pulses and materials. The first part focuses on femtosecond optical parametric amplification. A high power femtosecond optical parametric amplifier is demonstrated. A complete simulation approach is developed and demonstrated to successfully describe the output characteristics of the real optical parametric amplifier. This simulation approach is used as an analytic tool to investigate the dynamical interaction between material dispersion and three-wave nonlinear coupling during the amplification process. Several critical issues are addressed. A designed procedure of femtosecond optical parametric amplifiers is proposed. The second part focuses on the pulse-shaping phenomena of semiconductors. A high precision femtosecond laser pulse measurement technique is demonstrated. It is frequency-resolved optical gating based on two-beam coupling. Its precision and accuracy is examined before applying it to subsequent experiments. Pulse-shaping effects of gallium arsenide and semiconductor saturable absorber mirror have been successfully unveiled. Dielectric functions modified by photoexcited carriers are used to interpret experimental results. Observed pulse-shaping effects of semiconductor saturable absorber mirror are compared to theoretical prediction.Acknowledgements vii Abstract ix Table of contents xi List of figures xiv List of tables xvii Chapter 1 Introduction 1 Chapter 2 Experimental and theoretical investigations of femtosecond optical parametric amplifiers 5 2.1 Introduction 5 2.2 Experiments 9 2.2.1 Collinear phase-matched femtosecond optical parametric amplifier 10 2.2.2 Characterization: Inputs and outputs 12 2.3 Theoretical investigation 14 2.3.1 Nonlinear coupling wave equations and nonlinear optical polarizations 14 2.3.2 Simulation approach 19 2.4 Results and discussion 21 (A) Output pulse of the Ti:sapphire regenerative amplifier system 21 (B) Characteristics of the white-light seed pulse 22 (C) Comparison of the experimental and simulation results 25 (D) Coupling between material dispersion and optical nonlinearity 30 (E) Instability issues 37 (F) Unrealistic white-light seed pulse 43 (G) Pumped by chirp-free pulses 46 2.5 Design procedure of femtosecond optical parametric amplifiers 49 2.6 Conclusions 55 Appendix 2A 57 References 63 Chapter 3 Femtosecond pulse-shaping phenomena of semiconductors investigated by frequency-resolved optical gating based on two-beam coupling 67 3.1 Introduction 67 3.2 Theory and algorithm 73 3.2.1 Theory of two-beam coupling 73 3.2.2 The generalized projections algorithm 76 3.3 Experimental setup and procedure 80 3.4 Results and discussion 86 (A) Precision and accuracy analysis of the system 87 (B) Femtosecond pulse-shaping phenomena of GaAs 93 (C) Femtosecond pulse-shaping phenomena of semiconductor saturable absorber mirror 99 3.5 Conclusions 113 Appendix 3A 117 References 119 Chapter 4 Concluding remarks 12