Browsing by Author "Rocca, Jorge, advisor"
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Item Open Access Advancing the capability of high energy Yb:YAG lasers: multilayer coatings, pulse shaping and post compression(Colorado State University. Libraries, 2022) Wang, Hanchen, author; Rocca, Jorge, advisor; Roberts, Jacob, committee member; Lee, Siu Au, committee member; Marconi, Mario, committee memberRecently, cryogenically cooled Yb-doped amplifiers have been successfully scaled both in output energy and in repetition rate. The performance of such laser systems and their applications can be expanded by advancements in the development of optical coatings, that allow for scaling to higher pulse energies; as well as improvements in pulse shaping that include shorter pulse durations and the generation of programmable sequences of ultrashort pulses. This dissertation focuses on realizing the improvements mentioned above for cryogenic Yb:YAG amplifiers. First it reports the evaluation of ion beam sputtering (IBS) dielectric coatings for Yb:YAG at the environmental conditions in which cryogenic amplifiers are operated. The IBS coatings showed consistent performance in ambient, vacuum and cryogenic conditions, with damage threshold measured 20.4±0.6 J/cm2 for anti-reflection (AR) coating, and 27.4±1.3 J/cm2 for high reflector (HR) coating with 280 ps pulse duration at 77 K under the ISO:21254 standard. Second, a method for synthesizing trains of high energy compressed pulses was demonstrated and used to pump an 18.9 nm Ni-like Mo plasma-based soft x-ray laser more efficiently. The synthesized pulse increased the conversion efficiency of this spatially coherent soft x-ray source by 40%. Finally, femtosecond pulses were generated by post compression using a gas filled hollow core fiber (HCF), in which spectral broadening was achieved by self-phase modulation with an additional contribution from stimulated Raman scattering. Utilizing nitrogen gas as the non-liner medium, 300 mJ, 8 ps pulses were broadened to 3.7 nm and re-compressed to 460 fs by a grating compressor. The propagation and spectral broadening of high energy picosecond pulses in gas-filled HCFs were modeled and the results of simulations were compared with experiments.Item Open Access Demonstration of a compact 100 Hz, 0.1 J, diode-pumped picosecond laser(Colorado State University. Libraries, 2011) Curtis, Alden, author; Rocca, Jorge, advisor; Krapf, Diego, committee member; Yalin, Azer, committee memberIn this work I present an all laser diode pumped chirped pulse amplification laser system that is capable of producing 100 mJ laser pulses at 100 Hz repetition rate with durations of under 5 ps. The primary focus of this work consists of the development of two amplification stages that boost the temporally stretched pulses from a few hundred picoJoules to more than 100 mJ. The first amplifier is a Yb:YAG based regenerative amplifier operated at room temperature, which amplifies the pulses by a factor of about 106. The second stage is a multi-pass, Yb:YAG based amplifier, which is operated at cryogenic temperatures, and further amplifies the pulses by a factor of about 100. This is the first time a combination of room temperature and cryogenically cooled Yb:YAG amplifiers has been demonstrated. The room temperature pre-amplifier maintains more bandwidth than in the cryogenic case for increased compressibility. The cryogenic cooling of the power amplifier allows for increased heat dissipation and decreased saturation intensity for efficient operation. The optical efficiency of this amplifier is higher than that of other diode-pumped systems of comparable energy.Item Open Access Demonstration of filament-guided electrical discharges from a high average power 1 kHz picosecond laser(Colorado State University. Libraries, 2023) Dehne, Kristian A., author; Rocca, Jorge, advisor; Marconi, Mario, committee member; Brewer, Samuel, committee memberThe atmospheric propagation of ultrashort, high energy laser pulses is of interest for applications including remote sensing, directed energy, and the guiding of lightning. In this thesis, the filamentation of high energy picosecond laser pulses at repetition rates up to 1 kHz is demonstrated and the guiding of electrical discharges in air at high repetition rates is studied. The design and performance of the diode-pumped Yb:YAG chirped pulse amplification (CPA) system utilized for this experiment is also described. Diode-pumped solid state lasers in a CPA layout have emerged as the modern choice for the generation of high pulse energies at high repetition rates. For the work presented in this thesis, a high average power diode-pumped Yb:YAG laser system utilized for filament formation is de- tailed. The compact CPA system, which combines a room temperature regenerative amplifier and cryogenically cooled Yb:YAG amplifiers, results in compressed pulses of < 5 ps duration with up to 1.1 J of energy at 1 kHz repetition rate. This record Joule-level 1 kHz repetition rate picosecond laser (average power output of more than 1 kW) has enabled the results described herein. The application of this high average power Yb:YAG system for producing laser guided electrical discharges is the main focus of this thesis. The compressed output pulses from the Yb:YAG laser induce filamentation in air, resulting from the counterbalance between Kerr self-focusing and plasma refraction defocusing. The hydrodynamic response of the atmospheric air results in a density depression of similar geometry to the filament. The result is a preferential path which both triggers and guides electrical discharges. The majority of previous laser-guided discharge studies have been conducted at repetition rates of 10 Hz, where the medium completely recovers before the next laser pulse arrives. This thesis reports on the physics of laser filament-guided electric discharges in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of ∼7 ps duration at repetition rates up to 1 kHz. A breakdown voltage reduction of up to 4.2 X was measured and determined to result primarily from the perturbation caused by a single laser pulse, with cumulative effects playing only a secondary role. A current proportional to the laser pulse energy arises as soon as the laser pulse arrives, initiating a high impedance phase of the discharge channel evolution. Full breakdown, characterized by impedance collapse and the onset of high current conduction, occurs 100s of ns to a few μs later. The gaps between the filamentary plasma channel and the electrodes are observed to play a role in the delay between arrival of the laser pulse and the onset of a discharge. The breakdown voltages measured for 100 Hz and 1 kHz repetition rates are shown to be nearly equivalent. This is consistent with the results of interferometric analysis which shows that the filament formed by a single laser shot causes a deep density depression up to 75%, compared with the 20% density depression measured 10 μs prior to the arrival of a laser pulse in a sustained 1 kHz sequence. The physical insight gained from this work on the formation of laser filament-guided discharges in air at 1 kHz repetition rate can be expected to contribute to their use in applications.Item Open Access Development of a high energy diode-pumped chirped pulse amplification laser system for driving soft x-ray lasers(Colorado State University. Libraries, 2012) Reagan, Brendan A., author; Rocca, Jorge, advisor; Menoni, Carmen, committee member; Marconi, Mario, committee member; Krueger, David, committee memberThere is significant interest in the development of compact high repetition rate soft x-ray lasers for applications. This dissertation describes the development of a high energy, laser diode pumped, chirped pulse amplification laser system for driving soft x-ray lasers in the 10-20 nm spectral region. The compact laser system combines room temperature and cryogenically-cooled Yb:YAG amplifier to produce 1.5 Joule pulses at up to 50 Hz repetition rate. Pulse compression results in 1 J pulses of 5 ps duration. A room temperature pre-amplifier maintains bandwidth for short pulse operation and a novel cryogenic cooling technique for the power amplifier was developed to enable high average power operation of this laser. This laser was used to drive a soft x-ray laser on the 18.9 nm line of nickel-like molybdenum. This is the first demonstration of a soft x-ray laser driven by an all diode-pumped laser.Item Open Access Development of a high power chirped pulse amplification laser for driving secondary sources(Colorado State University. Libraries, 2019) Baumgarten, Cory M., author; Rocca, Jorge, advisor; Roberts, Jacob, committee member; Lee, Siu Au, committee member; Marconi, Mario, committee memberLaser applications which require high energy ultrashort laser pulses have been limited in repetition rate. This dissertation describes the development of high repetition rate, high energy, all diode pumped ultrashort pulse Yb:YAG lasers and their use in two selected applications. Yb:YAG is an attractive gain medium for high average power, ultrashort pulse laser operation. This material, with long upper level lifetime, is well suited for direct pumping by high power, narrow bandwidth laser diodes, and combined with a small quantum defect, minimal heating of the material is produced. Additionally, the thermal conductivity and optical properties of Yb:YAG dramatically improve when cooled to cryogenic temperatures. The main focus of this dissertation is the development of an all diode-pumped, chirped pulse amplification, ultrashort pulse laser based on a cryogenically-cooled Yb:YAG amplifier design. This laser system operates at λ = 1.03 μm and is capable of producing 1.4 J pulses before compression at 500 Hz and 1 kHz repetition rate. During 500 Hz operation, the laser used a combination of room temperature and cryogenically-cooled Yb:YAG amplifiers to generate pulses of 1 J energy compressed to sub- 5ps duration. At 1 kHz, pulse energies of 1 J with sub-10ps transform limited pulse durations were obtained. The simultaneously high pulse energies and repetition rates obtained in this work will be beneficial for a host of applications including tabletop sources of coherent short wavelength radiation, high power femtosecond sources operating in the near and mid-infrared, and high gradient laser plasma accelerators. The work in this dissertation specifically demonstrates the use of cryogenically cooled Yb:YAG lasers in the development of soft x-ray lasers and a near-infrared optical parametric amplifier for the testing damage threshold of multilayer coatings.The generation of coherent radiation in the soft x-ray regime was historically limited to 10 Hz. Compact, table-top soft x-ray lasers have enabled a range of applications including nano- scale imaging and lithography, the investigation of hot dense plasmas, and nano-scale fabrication. Recently, compact sources of coherent soft x-ray laser radiation were demonstrated at repetition rates of one hundred shots per second using the laser technology described in this dissertation. As a demonstration of the Yb:YAG laser's excellent beam quality and high average power, this system was used to pump a high repetition rate soft x-ray laser. The optical pump laser and the resulting soft x-ray laser, operated at a record 400 Hz repetition rate with strong lasing in the λ = 18.9 nm line of Ni-like Mo. This work also demonstrates a Yb:YAG laser driven, optical parametric chirped pulse amplification (OPCPA) laser system operating at 100 Hz in the near-infrared, which was used to per- form laser induced damage threshold measurements of optical coatings. OPCPAs have emerged as a next generation ultrafast laser source for generating sub-femtosecond laser pulses useful for probing molecular electron dynamics as well as creating ultra-intense, femtosecond laser pulses for exploring exotic states of matter and for the development of next generation laser plasma accelerators. The OPCPA developed as part of this work operates at wavelengths ranging from λ = 1.5-2 μm with final amplification stages pumped at 100 Hz with a chirped pulse amplification laser based on cryogenically-cooled Yb:YAG. The OPCPA was used to obtain damage thresholds of optical coatings in what to our knowledge constitutes the first results of picosecond damage performed in this wavelength range.Item Open Access Development of a high power high energy ultrafast laser(Colorado State University. Libraries, 2021) Chi, Han, author; Rocca, Jorge, advisor; Menoni, Carmen, committee member; Marconi, Mario, committee member; Lee, Siu Au, committee memberThis dissertation describes the development of high energy, high repetition rate laser technology based on cryogenically cooled diode-pumped Yb:YAG laser amplifiers. The key challenges of thermal management, the generation of high energy green pulses at high repetition rate, and the design of an ultrafast laser amplifier that uses the green pulses as pump are discussed in this dissertation. To aid the development of thermal management solutions, an accurate, in situ, noninvasive optical technique to generate three-dimensional (3-D) temperature maps of cryogenic amplifiers during operation at high average power was demonstrated. The temperature is determined by analyzing the fluorescence spectra of the laser material (Yb:YAG) with a neural network algorithm. The accuracy of the technique relies on a calibration that does not depend on simulations. Results are presented for a cryogenic Yb:YAG active mirror laser amplifier operating at different pump conditions, which include kW pump power level operation. Based on this temperature measurement technique, an analysis of the thermal behavior of a high-energy kilowatt-average-power diode-pumped cryogenically cooled Yb:YAG active mirror laser amplifier is presented. Maps of the temperature distribution in the laser amplifier crystal at pump powers up to 1kW were obtained for the first time by spectrally resolving the fluorescence induced by a scanning probe beam. The cryo-temperature measurement technique is applicable to other solid-state lasers materials. The wavefront distortions resulting from the front surface deformation and the overall deformation of the gain medium assembly were measured using a Mach–Zehnder interferometer. The measured deformations agree well with the results of finite element thermomechanical modeling simulations, and with the results of focal length shift measurements. The relative contributions to the optical path difference (OPD) of the mechanical deformations, refractive index changes, and electronic contribution are discussed. The pump-induced mechanical deformations of the assembly dominate the OPD changes in the kilowatt-average-pump-power cryogenically cooled Yb:YAG active mirror laser investigated. The generation of green (λ= 515 nm) Joule-level pulses at 1 kHz repetition rate was demonstrated. This was achieved by frequency doubling 1.2 J, 2 ns temporally shaped square pulses from a cryogenically cooled Yb:YAG laser in an LBO crystal. The generation of 0.94 J second-harmonic pulses at 1 kHz was demonstrated with 78% conversion efficiency. The unconverted light was sent through a second LBO crystal to generate an additional >100 mJ second-harmonic pulses to reach a total green average power of 1.04kW. A higher conversion efficiency of 89% was also achieved for 0.58 J green pulses at 1 kHz. An application of this green laser is the pumping of high average power ultrafast laser amplifiers. The design of a two-stage water-cooled Ti:Sapphire amplifier system to generate 300 mJ pulses pre-compression using this green laser as pump is discussed. The simulation of the gain and thermal distribution of the 1st and 2nd stage amplifier are presented. The first experimental results of the operation of the first amplification stage of this laser system are discussed.Item Open Access Development, characterization and application of a high average power capillary discharge soft x-ray laser(Colorado State University. Libraries, 2001) Benware, Brady Robert, author; Rocca, Jorge, advisorA compact high repetition rate, high average power capillary discharge laser operating at a wavelength of 46.9 nm that is of the size of many widely utilized visible and UV lasers has been developed and characterized. Two significant differences from previously developed capillary discharge soft x-rays lasers, the use of ceramic capillaries rather than poly-acetal and significantly longer plasma columns of up to 36 cm, allowed for the generation of greatly increased output pulse energies and average power. Lasing at a repetition rate of 4 Hz and an average laser pulse energy of 0.88 mJ has been obtained, which amounts to an average power of 3.5 mW. Lasing at repetition rates as high as 10 Hz was also achieved, but with lower output pulse energy. In this work the beam energy and divergence were measured as a function of capillary length, and the temporal evolution of the laser pulse was also studied. The combined high pulse energy and high repetition rate of this laser make it unique in the field of soft x-ray lasers to date. This laser has been used to perform angular dependent reflectivity measurements to determine optical constants of materials at 46.9 nm, which are in good agreement with those previously measured, or in some cases represent the first recorded values at this wavelength. This experiment constitutes the first application of a table-top soft x-ray laser to the field of material characterization. In a separate experiment, the output beam was polarized using two multi-layer coated mirrors that were configured for optimum reflectivity at 45 degrees. The resulting 96% polarized beam was then used to characterize the efficiency of a diffraction grating. Finally, in a third experiment, the beam was focused using a spherical multi-layer coated mirror to a spot size where the majority of the energy was confined to a 2 μm diameter. The peak intensity was estimated to be 1x1011 W/cm2. Through ray tracing computations, the focused spot size was determined to be dominated by spherical aberration. This focused beam reached intensities that were sufficient to induce ablation on brass and stainless steel targets realizing the first demonstration of material ablation with a coherent soft x-ray beam.Item Open Access Instrumentation for ultra-intense laser matter interaction studies at high repetition rates(Colorado State University. Libraries, 2022) Nedbailo, Ryan, author; Rocca, Jorge, advisor; Marconi, Mario, committee member; Yalin, Azer, committee memberA new class of high-repetition rate (HRR) Peta-Watt-class (PW) laser systems make it possible to study laser matter interaction processes, like laser ion acceleration (LIA) and laser plasma instabilities (LPI), at unprecedented rates. These systems have the potential to generate immense amounts of data through rapid multivariable parameters scans of laser energy, pulse shape, spot size and others, in order to better diagnose and characterize the conditions underlying LPI and LIA. However, detection media, typically image plates, film, CR-39, presently limits the repetition rate at which data can be collected from these systems. Rep-rated diagnostics are being redesigned to match the capabilities of current multi-Hz present and near future, PW-class laser systems. Here we present the development of a compact Thomson Parabola Ion Spectrometer capable of characterizing various ion species of multi-MeV ion beams from >10^20 W/cm^2 laser produced plasmas at rates commensurate with the laser operation rates. This diagnostic makes use of a Polyvinyltoluene (PVT) based fast plastic scintillator (EJ-260), where the emitted light is collected by an optical imaging system coupled to a thermoelectrically cooled scientific complementary metal–oxide–semiconductor (sCMOS) camera. This offers a robust solution for data acquisition at HRR while avoiding the added complications and non-linearities of microchannel plate (MCP) based systems. Different ion energy ranges can be probed using the modular magnet setup, variable electric field, and a varying drift-distance. We have demonstrated operation and data collection with this system at up to 0.2 Hz from plasmas created by irradiating a solid target, limited only by the motorized target motion system. With the appropriate software and the use of machine learning techniques, on-the-fly ion spectral analysis will be possible, enabling real-time experimental control. The diagnostic design, calibration, and results from experiments at the ALEPH laser facility at Colorado State University (CSU) are presented. In addition, we describe the results of the development of a novel scheme for the generation of spike trains of uneven delay (STUD) laser pulses using an array of hexagonal mirrors. By individually driving the offset of each mirror segment, we can divide the wavefront of the laser creating a pulse train of arbitrary delay. This pulse-train forming device can be used to conduct experiments related to a proposed method of mitigating the effects of LPI for inertial confinement fusion (ICF). By periodically turning on and off the laser drive of the ICF process, it has been postulated that the growth of parametric instabilities can be mitigated by allowing damping during the off-cycle of the STUD pulses. The use of the pulse-train forming scheme demonstrated here will allow us to study the effects of pulse train delay and duration best suited to LPI mitigation.