Measurement of complex ultrashort laser pulses using frequency-resolved optical gating
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This thesis contains three components of research: a detailed study of the performance of Frequency-Resolved Optical Gating (FROG) for measuring complex ultrashort laser pulses, a new method for measuring the arbitrary polarization state of an ultrashort laser pulse using Tomographic Ultrafast Retrieval of Transverse Light E-fields (TURTLE) technique, and new approach for measuring two complex pulses simultaneously using PG blind FROG. In this thesis, we compare the performance of three versions of FROG to measure complex ultrashort laser pulses: second-harmonic-generation (SHG) FROG, polarization-gate (PG) FROG, and cross-correlation FROG (XFROG). We found that the XFROG algorithm achieves 100% convergence, while PG FROG and SHG FROG GP algorithm achieve 100% convergence after doing the noise deduction and increasing the sampling range. The second part of this thesis describes a method for measuring the intensity, phase and the complete polarization state of a laser pulse having a time-dependent polarization state (i.e. a polarization shaped pulse). This technique is called tomographic ultrafast retrieval of transverse light E-fields (TURTLE). TURTLE typically involves making three FROG measurements: one of the intensity and phase of the pulse's horizontal polarization component, one of its vertical component, and another of the 45o component. Performing a simple minimization using these three FROG measurements, the time-dependent polarization state of the ultrashort pulse can be determined. The third part of this thesis introduces a method for measuring two complex pulses simultaneously using a single FROG device. This technique is based on Polarization-gate (PG) FROG and it is called PG blind FROG. It involves two measurements: One of them is a PG FROG trace using the intensity of pulse 1 to gate pulse 2 and other one is the PG FROG trace using the intensity of pulse 2 to gate pulse 1. An iterative phase retrieval algorithm based on generalized projection (GP) is used to reconstruct the intensity and phase of these two pulses. This approach is an elegant way to measure complex and/or very spectrally broad pulses such as those due to super continuum.