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ItemSingle-frame complete spatiotemporal measurement of complex ultrashort laser pulses(Georgia Institute of Technology, 2016-04-01) Guang, ZheToday one of the frontiers in light measurement is to measure ultrashort pulses from ultrafast laser systems, which demonstrate extremely fast temporal variations, and are necessarily associated with large spectral bandwidths by Fourier transform. In addition to the temporal and spectral structures, ultrashort pulses can also be complex in space. Especially, the field can have spatiotemporal couplings which relate pulse temporal profile to spatial coordinates. Therefore, a complete spatiotemporal measurement technique is needed. In this work, we demonstrate our study on measuring complex ultrashort pulses by development of a method, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). Based on digital holography, this simple single-frame method can measure the complete spatiotemporal intensity I(x,y,t) and phase ϕ(x,y,t) of pulses at a particular z-plane. By experiments, we investigated sub-picosecond chirped pulse beating, pulses from multimode optical fibers, ultrafast lighthouse effect and so on, using STRIPED FISH. We also performed numerical simulations to understand the effects of different spatiotemporal distortions on STRIPED FISH trace. With its improved apparatus, processing algorithm, and display method, STRIPED FISH offers a simple and compact solution to monitor, measure, and display spatiotemporal structures in ultrashort pulses.
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ItemTroubleshooting ultrashort pulse measurement: the coherent artifact and other issues(Georgia Institute of Technology, 2016-03-14) Rhodes, Michelle AnnTheoretical limitations of several ultrashort pulse measurement techniques are investigated. Particular attention is paid to the consequences of averaging over many pulses of different shapes. Averaging over many pulses is a very common practice, and if the pulse shape varies then the measurement result will be incorrect. This issue, referred to as a coherent artifact, is simulated for frequency-resolved optical gating using several nonlinearities, spectral interferometry for direct electric field reconstruction, two-dimensional spectral shearing interferometry, self-referenced spectral interferometry using cross-polarized wave generation, and multiphoton intrapulse interference phase scan. The role of measurement feedback in identifying pulse-shape instability is explored where possible. Several techniques receive additional analysis, such as searching for ambiguities or simulating convergence conditions. In addition, a method for intuitively displaying spatiotemporally distorted pulses is explored and developed.
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ItemSingle-shot measurements of complex pulses using frequency-resolved optical gating(Georgia Institute of Technology, 2013-11-07) Wong, Tsz ChunFrequency-resolved optical gating (FROG) is the standard for measuring femtosecond laser pulses. It measures relatively simple pulses on a single-shot and complex pulses using multi-shot scanning and averaging. However, experience from intensity autocorrelation suggests that multi-shot measurements may suffer from a coherent artifact caused by instability in the laser source. In this thesis, the coherent artifacts present in modern pulse measurement techniques are examined and single-shot techniques for measuring complex pulse(s) are proposed and demonstrated. The study of the coherent artifact in this work shows that modern pulse measurement techniques also suffer from coherent artifacts and therefore single-shot measurements should be performed when possible. Here, two single-shot experimental setups are developed for different scenarios. First, an extension of FROG is developed to measure two unknown pulses simultaneously on a single-shot. This setup can measure pulses that have very different center wavelengths, spectral bandwidths, and complexities. Second, pulse-front tilt is incorporated to extend the temporal range of single-shot FROG to tens of picoseconds which traditionally can only be attained by multi-shot scanning. Finally, the pulse-front tilt setup is modified to perform a single-shot measurement of supercontinuum, one of the most difficult pulses to measure due to its long temporal range, broad spectral bandwidth, and low pulse energy.
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ItemOptical-parametric-amplification applications to complex images(Georgia Institute of Technology, 2011-07-01) Vaughan, Peter MatthiasWe have used ultrafast optics, primarily focused on the nonlinear processes of Polarization Gating and of Optical Parametric Amplification, one for measurement and the other for imaging purposes. For measurement, we have demonstrated a robust method of measurement to simultaneously measure both optical pulses used in a pump-probe type configuration. We refer to this method of pulse measurement as Double Blind Polarization Gating FROG. We have demonstrated this single-shot method for measuring two unknown pulses using one device. In addition to pulse measurement, we have demonstrated the processes of Optical Parametric Amplification (OPA) applicability to imaging of complex objects. We have done this where the Fourier transform plane is used during the interaction. We have amplified and wavelength converted a complex image. We observe a gain of ~100, and, although our images were averaged over many shots, we used a single-shot geometry, capable of true single-shot OPA imaging. To our knowledge, this is the first Fourier-plane OPA imaging of more than a single spatial-frequency component of an image. We observe more than 30 distinct spatial frequency components in both our amplified image and our wavelength shifted image. We have demonstrated all-optical spatial filtering for these complex images. We have demonstrated that direct Fourier filtering of spatial features is possible by using a shaped pump beam. We can isolate certain portions of the image simply by rotating the crystal.
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ItemPulse compression and dispersion control in ultrafast optics(Georgia Institute of Technology, 2011-01-22) Chauhan, Vikrant Chauhan KumarPulse Compression and Dispersion Control in Ultrafast Optics Vikrant K. Chauhan 116 Pages Directed by Dr. Rick P. Trebino In this thesis, we introduced novel pulse compressors that are easy to align and which also compensate for higher order dispersion terms. They use a single dispersive element or a combination of dispersive elements in single-element-geometry. They solve the problem of extra-cavity pulse compression by providing control of the pulse width in almost all of the experiments performed using ultrashort pulses, and they even compensate for higher order dispersion. We performed full spatiotemporal characterization of these compressors and demonstrated their performance. We also developed a theoretical simulation of pulse compressors which is based on a matrix based formalism. It models the full spatiotemporal characteristics of any dispersion control system. We also introduced a simple equation, in its most general form, to relate the total dispersion and magnification introduced by an arbitrary sequence of dispersive devices. Pulse compressor characterization was done using interferometric measurements in the experiments presented in this work, but we also developed a method to measure pulses that uses polarization gating FROG for measuring two unknown pulses. In the last part, we briefly discuss the designing of a high energy chirped pulse amplification system.
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ItemMeasuring the electric field of picosecond to nanosecond pulses with high spectral resolution and high temporal resolution(Georgia Institute of Technology, 2010-10-08) Cohen, Jacob ArthurWe demonstrate four experimentally simple methods for measuring very complex ultrashort light pulses. Although each method is comprised of only a few optical elements, they permit the measurement of extremely complex pulses with time-bandwidth products greater than 65,000. First, we demonstrate an extremely simple frequency-resolved-optical gating (GRENOUILLE) device for measuring the intensity and phase of pulses up to ~20ps in length. In order to achieve the required high spectral resolution and large temporal range, it uses a few-cm-thick second harmonic-generation crystal in the shape of a pentagon. This has the additional advantage of reducing the device's total number of components to three. Secondly, we introduce a variation of spectral interferometry (SI) using a virtually imaged phased array and grating spectrometer for measuring long complex ultrashort pulses up to 80 ps in length. Next, we introduce a SI technique for measuring the complete intensity and phase of relatively long and very complex ultrashort pulses. It involves making multiple measurements using SI (in its SEA TADPOLE variation) at numerous delays, measuring many temporal pulselets within the pulse, and concatenating the resulting pulselets. Its spectral resolution is the inverse delay range--many times higher than that of the spectrometer used. The waveforms were measured with ~ fs temporal resolution over a temporal range of ~ns and had time-bandwidth products exceeding 65,000, which to our knowledge is the largest time-bandwidth product ever measured with ~fs temporal resolution. Finally, we demonstrate a single-shot measurement technique that temporally interleaves hundreds of measurements with ~fs temporal resolution. It is another variation of SI for measuring the complete intensity and phase of relatively long and complex ultrashort pulses in a single shot. It uses a grating to introduce a transverse time delay into a reference pulse which gates the unknown pulse by interfering it at the image plane of an imaging spectrometer. It provided ~125 fs temporal resolution and a temporal range of 70 ps using a low-resolution spectrometer.