High energy ultrashort pulses can generate filaments during propagation, plasma channels which balance self-focusing to allow laser light propagation at a clamped diameter and intensities exceeding 10^13 W/cm^2 for many times the Rayleigh length. These filaments are attractive options for laser ablation at a distance but are limited in the total energy that can be delivered to a single point on target. In this work, temporally structuring femtosecond pulses into gigahertz bursts of spatially overlapped filaments lead to an increase in ablation. Material-interaction effects are compared between these nanosecond duration bursts of femtosecond pulses and traditional nanosecond pulses of similar total energy and duration in both aluminum and silicon targets.
The majority of filamentation studies have focused on near infrared (NIR) filaments, which have been demonstrated to propagate over many times the Rayleigh range with clamped intensity, electron plasma density, and beam diameter. Long wavelength infrared (LWIR) laser light sources, however, have not been extensively studied for filamentation. Here, we discuss filamentation in both wavelength regimes and introduce a new ultrafast CO2 system capable of producing high-power 10 µm picosecond pulses. Future work is outlined which will significantly increase the output power of the CO2 laser for upcoming studies and allow direct comparison of NIR and LWIR filaments.
Filaments, formed by ultrashort pulsed laser (USPLs) with high peak powers, deliver high intensities and a plasma channel to km-scale distance, without the need for focusing elements. These properties make them viable for long-range outdoor applications, including propagation to or at high altitudes where air pressure is a fraction of that at sea level. Since filament formation and characteristics are known to vary with air pressure, here, we analyze how critical filamentation thresholds and properties change as pressure decreases, through experiment and simulation. This study indicates that filament applications are indeed feasible over long distances to or at high altitudes.
Recently, the technique of infrared/terahertz Double Resonance Spectroscopy (DRS) was proposed for remote sensing of trace gases in atmospheric conditions. The atmospheric window of transmission is in the 9-11 µm range, which makes CO2 lasers highly suited for this application. DRS is a valuable detection method because of increased measurement specificity due to terahertz ro-vibrational signature detection. Preliminary DRS measurements utilizing a pulsed CO2 laser source with a known trace gas in a vacuum chamber are discussed. A plan is then presented for future DRS experiments at ambient pressure using ultrafast laser techniques.
Laser filaments generated by ultrashort pulse (USP) lasers achieve diffractionless propagation for distances surpassing the Rayleigh distance, making them highly beneficial to long-range outdoor applications. However, filaments generated by a single USP are limited to a clamped electron density, intensity, and lifetime. Here, we demonstrate how spatial and temporal engineering can overcome these limitations and enhance a variety of filament applications. We also prove the robustness of structured filaments in propagation studies on a turbulent, kilometer scale range. A strong understanding of beam engineering and generating structured filaments has the potential to improve many applications.
Laser filaments generate intensities at remote distances that exceed the plasma and ablation thresholds of solid materials, but intensity clamping limits the impact of a single pulse. To overcome this fundamental restraint, we have engineered a high-energy solid-state Titanium:Sapphire laser to generate nanosecond-duration bursts of ultrashort pulses. This temporal structuring of the laser energy enhances nonlinear propagation and several interaction mechanisms with solid targets including ablation, acoustic shockwave production, and remote RF generation. This presentation will discuss the impact of the pulse parameters and burst format on these effects in both low and high-altitude environments through experiments and simulations.
This work presents the initial activation of the Mobile Ultrafast High-Energy Laser Facility (MU-HELF) located on a 1 km test range at the Townes Institute Science and Technology Experimentation Facility (TISTEF). The MU-HELF was designed to study nonlinear laser propagation effects including filamentation and produces pulses at 800 nm with current peak powers as high as 5 TW. The pulse width, energy, size, and focusing conditions of the launched beams are all readily adjustable. Several data collection techniques have been implemented that enable high-resolution, single-shot beam profiles, spectra, and energy measurements at any point along the range. Atmospheric conditions are also continuously measured during laser propagation using the array of monitoring equipment available at TISTEF. The newly active test facilities and data collection procedures demonstrated here will drive future in-depth high-intensity laser propagation studies and development of field-deployable applications.
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