Long Wave Infrared Pulse Compression and Nonlinear Propagation of Nontrivial Optical Waveforms

Abstract

In this dissertation new frontiers in laser physics are explored with an emphasis onlong-wave infrared (LWIR) pulse propagation in gaseous media in the extreme nonlinear optics regime. Numerical experiments are used to study physics which the results from these simulations should motivate experiments. The study comprises of four main primary research objectives: 1. Terawatt-level few-cycle pulse compression of LWIR using a gas-filled multi-pass cell. 2. Formation of X-waves from LWIR pulses in Xenon and Air. 3. Probing the transition from nonlinearly dominated (gKPE) to dispersion dominated (NLSE) physics by engineering a monotonically increasing dispersion profile using the Sellmeier equation parameters. 4. Synthesizing exotic optical waveforms from harmonics of a LWIR fundamental wavelength to generate terahertz radiation mediated by multi-color pulse filamentation. Starting from currently available CO2 laser pulses, propagation in a gas-filled multipass cell is simulated. A laser pulse with a central wavelength in the LWIR is shown to be compressed in a controlled way to sub-100 fs duration and contain multiple terawatts of peak power at the output. The simulated gas-filled multi-pass cell is filled with the second most abundant isotope of CO2, which allows for long distance, low-loss propagation in the compression chamber. By using a multi-pass cell filamentation is avoided, so that laser induced damage of mirrors is avoided and the resulting ultrashort pulse can be extracted from the cell. The compression is caused by selfcompression, mediated by the balance of anomalous dispersion of the propagation medium and the normal dispersion produced by self-phase modulation (SPM). The cavity mirrors act to control the beam shape and intensity to maximize SPM while avoiding filamentation. Using the sub-100 fs duration pulse generated by the gas-filled multi-pass cell as an input, numerical experiments showed that a broadband, multiharmonic spanning X-wave forms during optical filamentation collapse in Xenon and Air. A self-contained X-wave pulse is generated during regularization of optical field shocking in the form of a dispersive wave being shed out the back of the pulse. Next, the transition that marks the origination point of the X-wave is studied further. It is determined that by engineering a monotonically increasing dispersion profile so that the group velocity dispersion (GVD) becomes larger and more curved the transition from gKPE to NLSE can be moved to longer wavelengths. With sufficiently large GVD (dispersion dominated vs nonlinearity dominated regimes) the multi-harmonic spanning X-wave reverts to a common single-harmonic X-wave. Finally, exotic waveforms, akin to those found in RF communication (square, triangle, sawtooth, etc.), are simulated in Xenon and shown to generate THz efficiently as the carrier-envelope phase offset is tuned, pulse duration decreases, and number of harmonics increases. This results in an even broader spectrum that includes the multi-harmonic spanning X-wave. The spectral extent from the multi-color pulse filamentation starting from a LWIR fundamental stretches remarkably from the THz all the way to the deep UV.