COMPLETE TEMPORAL MEASUREMENT OF LOW-INTENSITY AND HIGH-FREQUENCY ULTRASHORT LASER PULSES
Jones, Travis N.
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Two important frontiers in the field of ultrashort pulse measurement are the complete temporal measurement of low-intensity picosecond pulses in the near-infrared (NIR) and intense ultrashort pulses in the ultraviolet (UV) and extreme ultraviolet (EUV). The former are projected to find great use in the field of optical telecommunications, while the latter are the result of the relatively recent development of bright, coherent light sources in this wavelength range. The challenge in measuring weak pulses in the NIR is that many measurement techniques require expensive electronics and/or are complicated and difficult to align. UV pulse measurement on the other hand, due to the higher photon energies involved, is primarily hindered by slow light-matter interactions such as absorption or photoionization. In this thesis, we develop and present two novel pulse-measurement techniques based on the widely-used method of Frequency-Resolved Optical Gating (FROG) which are aimed at addressing these challenges. The first technique, called Collinear GRENOUILLE, is an experimentally-simple and sensitive device which tests the sensitivity of second harmonic generation to measure low-intensity, picosecond pulses in the NIR. The measurement capabilities of Collinear GRENOUILLE are experimentally demonstrated by the successful measurement moderately complex pulses with femtojoule pulse energies at 800 nm. A similar measurement is also presented at 1030 nm where more efficient nonlinear crystals exist. The second technique, known as Induced-Grating Cross-correlation FROG, is designed to measure intense laser pulses in the UV and EUV. To demonstrate this technique, we first perform measurements of chirped 400 nm pulses in a fast-responding nonlinear medium. We show that the resulting traces contain the complete electric field of the UV pulse we intended to measure. We further confirm these measurement by developing a modified phase-retrieval algorithm to reconstruct the pulse from the measured traces. Next, we performed similar measurements in a slowly-responding medium. FROG typically requires a fast nonlinear-optical processes to measure pulses, however once the response of the medium in accounted for, the measurements made using the IG XFROG technique indicate that accurate measurements of the pulse can still be made using a slow light-matter interaction. In the case of slow media, the IG XFROG technique is first demonstrated using absorption from amplified pulses at 400 nm and 267 nm. After establishing feasibility at these wavelengths, we applied this technique to EUV laser pulses from the FERMI free-electron laser at 31.3 nm, for which the dominant light-matter interaction is photoionization.