We have successfully developed a laser system to produce pulses with a wavelength centered at 800... more We have successfully developed a laser system to produce pulses with a wavelength centered at 800 nm, energies above 15 J, temporally compressed to 75 fs and focused to power densities beyond 10 21 W/cm 2. Enabling technologies include chirped-pulse amplification (CPA), 10 cm aperture Ti:Al 2 O 3 crystals, large diffraction gratings, and an energetic Nd:glass laser for pumping the final two amplifiers. Measurements of the compressed pulse spectrum, frequency resolved optical gating (FROG) diagnostic, and focal spot are presented. We have also investigated and developed a technique for suppression of transverse parasitic lasing in large-aperture Ti:sapphire crystal amplifiers. PACS: 42.65.Re; 52.40.Nk; 41.85.Ew The principal activity of our research group at Lawrence Liv-ermore National Laboratory (LLNL) is directed at the study of high-energy-density matter with an emphasis on equation of state and opacity. The use of ultra-short-pulse laser-matter interactions can provide a new technique for the creation of high-energy-density plasmas in the laboratory. Our efforts are differentiated from other LLNL laser facilities in that we utilize prepulse clean 50 to 150 fs laser pulses to deposit energy in solid density matter prior to the plasma expansion. To further this research, we have developed a novel short-pulse laser capable of focal intensities in excess of 10 21 W/cm 2 with energies on target in escess of 15 J. We refer to the laser system as " JanUSP " , so named since we are using one arm of our " Janus " Nd:glass laser system as a pump source for the final two stages of an ultra-short-pulse (USP) laser system. This system was conceived more than seven years ago and takes advantage of several technological advancements developed since then. While waiting for the development of suitable optical components, we experimented with a smaller-scale CPA system and various final amplifier schemes, including flashlamp-pumped Ti:sapphire [1] and Nd:glass laser-pumped Ti:sapphire [2, 3]. The latter of these schemes has been in use at our USP laser facility for over four years and has proven to be a robust source for the generation of power densities > 10 19 W/cm 2. Chirped-pulse amplification laser systems have extensively evolved and matured since the mid-1980s. The two gain media most commonly employed for CPA are Nd:glass and Ti:sapphire. Recently, the scaling of a CPA Nd:glass system to very high intensity (≈ 2 × 10 20 W/cm 2) has been achieved with large-aperture disk amplifiers (46 cm diameter) on the Petawatt Laser Project at LLNL [4]. Many factors must be considered when selecting laser amplifier media. Generally speaking, when comparing Ti:sapphire to Nd:glass, the gain bandwidth of Ti:sapphire is more than 10 times that of Nd:glass; saturation fluence (E s) is ≈ 1 J/cm 2 for Ti:sapphire and ≈ 5 J/cm 2 for Nd:glass [5], and the small-signal power gain coefficient(g 0) is much greater for Ti:sapphire. Until now, efforts to scale titanium-based laser systems to intensities greater than 10 19 W/cm 2 have concentrated on reducing the amplified pulsewidth to less than 20 fs [6, 7], because significantly higher pulse energies have been limited by the availability of large-aperture crystals with high optical quality. Here, we report on a CPA laser system which utilizes the largest Ti:sapphire disk amplifiers ever produced (10 cm diameter). Optimization of disk amplifiers with larger aspect ratios (transverse to longitudinal) and increased pump energy, becomes increasingly difficult as suppression of parasitic las-ing becomes a key challenge. Ti:sapphire amplifiers are typically longitudinally pumped by Q-switched neodymium oscillators frequency doubled to ≈ 530 nm, which is near the titanium absorption peak. Larger pump sources append flashlamp-pumped Nd:glass amplifiers to the oscillator before frequency doubling. Beam profiles from Ti:sapphire amplifier stages can also be effectively shaped by adjusting the size, position and profile of the pumping beams; however, poorly shaped pump profiles can deleteriously affect the disk amplifier's spatial gain uniformity.
We have successfully developed a laser system to produce pulses with a wavelength centered at 800... more We have successfully developed a laser system to produce pulses with a wavelength centered at 800 nm, energies above 15 J, temporally compressed to 75 fs and focused to power densities beyond 10 21 W/cm 2. Enabling technologies include chirped-pulse amplification (CPA), 10 cm aperture Ti:Al 2 O 3 crystals, large diffraction gratings, and an energetic Nd:glass laser for pumping the final two amplifiers. Measurements of the compressed pulse spectrum, frequency resolved optical gating (FROG) diagnostic, and focal spot are presented. We have also investigated and developed a technique for suppression of transverse parasitic lasing in large-aperture Ti:sapphire crystal amplifiers. PACS: 42.65.Re; 52.40.Nk; 41.85.Ew The principal activity of our research group at Lawrence Liv-ermore National Laboratory (LLNL) is directed at the study of high-energy-density matter with an emphasis on equation of state and opacity. The use of ultra-short-pulse laser-matter interactions can provide a new technique for the creation of high-energy-density plasmas in the laboratory. Our efforts are differentiated from other LLNL laser facilities in that we utilize prepulse clean 50 to 150 fs laser pulses to deposit energy in solid density matter prior to the plasma expansion. To further this research, we have developed a novel short-pulse laser capable of focal intensities in excess of 10 21 W/cm 2 with energies on target in escess of 15 J. We refer to the laser system as " JanUSP " , so named since we are using one arm of our " Janus " Nd:glass laser system as a pump source for the final two stages of an ultra-short-pulse (USP) laser system. This system was conceived more than seven years ago and takes advantage of several technological advancements developed since then. While waiting for the development of suitable optical components, we experimented with a smaller-scale CPA system and various final amplifier schemes, including flashlamp-pumped Ti:sapphire [1] and Nd:glass laser-pumped Ti:sapphire [2, 3]. The latter of these schemes has been in use at our USP laser facility for over four years and has proven to be a robust source for the generation of power densities > 10 19 W/cm 2. Chirped-pulse amplification laser systems have extensively evolved and matured since the mid-1980s. The two gain media most commonly employed for CPA are Nd:glass and Ti:sapphire. Recently, the scaling of a CPA Nd:glass system to very high intensity (≈ 2 × 10 20 W/cm 2) has been achieved with large-aperture disk amplifiers (46 cm diameter) on the Petawatt Laser Project at LLNL [4]. Many factors must be considered when selecting laser amplifier media. Generally speaking, when comparing Ti:sapphire to Nd:glass, the gain bandwidth of Ti:sapphire is more than 10 times that of Nd:glass; saturation fluence (E s) is ≈ 1 J/cm 2 for Ti:sapphire and ≈ 5 J/cm 2 for Nd:glass [5], and the small-signal power gain coefficient(g 0) is much greater for Ti:sapphire. Until now, efforts to scale titanium-based laser systems to intensities greater than 10 19 W/cm 2 have concentrated on reducing the amplified pulsewidth to less than 20 fs [6, 7], because significantly higher pulse energies have been limited by the availability of large-aperture crystals with high optical quality. Here, we report on a CPA laser system which utilizes the largest Ti:sapphire disk amplifiers ever produced (10 cm diameter). Optimization of disk amplifiers with larger aspect ratios (transverse to longitudinal) and increased pump energy, becomes increasingly difficult as suppression of parasitic las-ing becomes a key challenge. Ti:sapphire amplifiers are typically longitudinally pumped by Q-switched neodymium oscillators frequency doubled to ≈ 530 nm, which is near the titanium absorption peak. Larger pump sources append flashlamp-pumped Nd:glass amplifiers to the oscillator before frequency doubling. Beam profiles from Ti:sapphire amplifier stages can also be effectively shaped by adjusting the size, position and profile of the pumping beams; however, poorly shaped pump profiles can deleteriously affect the disk amplifier's spatial gain uniformity.
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