This talk will provide an overview of high power laser research at Lawrence Livermore National Laboratory (LLNL). It will discuss the status of the National Ignition Facility (NIF) laser. In addition, the talk will describe other laser development activities such as the development of high average power lasers and novel fiber lasers.
The National Ignition Facility (NIF) has been in service since 2007 and operating with > 1 MJ energies since 2009. During this time the facility has transitioned to become an international user facility and increased the shot rate from ~150 target shots per year to greater than 400 shots per year. Today, the NIF plays an essential role in the US Stockpile Stewardship Program, providing data under the extreme conditions needed to validate computer models and train the next generation of stockpile stewards. Recent upgrades include the Advanced Radiographic Capability (ARC), a high energy short pulse laser used to do high resolution radiography.
In addition to the NIF, this talk will include an overview of progress on the high average power laser development, recent results from fiber laser development activities and improvements to laser design and computational capabilities.
The National Ignition Facility (NIF) is a high-power, 192-beam laser facility being built at the Lawrence Livermore National Laboratory. The 192 laser beams that will converge on the target at the output of the NIF laser system originate from a low power fiber laser in the Master Oscillator Room (MOR). The MOR is responsible for generating the single pulse that seeds the entire NIF laser system. This single pulse is phase-modulated to add bandwidth, and then amplified and split into 48 separate beam lines all in single-mode polarizing fiber. Before leaving the MOR, each of the 48 output pulses are temporally sculpted into high contrast shapes using Arbitrary Waveform Generators (AWG). Each output pulse is then carried by optical fiber to the Preamplifier Module (PAM) where it is amplified to the multi-joule level using a diode-pumped regenerative amplifier and a multi-pass, flashlamp-pumped rod amplifier. Inside the PAM, the beam is spatially shaped to pre-compensate for the spatial gain profile in the main laser amplifiers. The output from the PAM is sampled by a diagnostic package called the Input Sensor Package (ISP) and then split into four beams in the Preamplifier Beam Transport System (PABTS). Each of these four beams is injected into one of NIF's 192 beam lines. The combination of the MOR, PAM, ISP and PABTS constitute the Injection Laser System (ILS) for NIF. This system has proven its flexibility of providing a wide variety of pulse shapes and energies during the first experiments utilizing four beam lines of NIF.
The electron-beam pumped XeF(C yields A) excimer has been investigated as a novel gain medium for ultrashort pulse, high power amplification in the visible spectral region over a wide range of laser pulse durations. Gain measurements for 100 ps and 800 fs pulses resulted in a small signal gain coefficient of 3%/cm and a saturation energy density of 80 mJ/cm2. For 250 fs pulses, a saturation energy density of 50 mJ/cm2 was observed. Narrowband absorbers in the XeF(C yields A) spectrum could be bleached out, yielding a smooth gain profile of 60 nm bandwidth. An unstable resonator was designed with particular consideration of the small XeF(C yields A) gain coefficient and optimized energy extraction in a single pulse output. A maximum pulse energy of 275 mJ was obtained by amplification of 250 fs pulses at 490 nm wavelength, generating laser powers in the terawatt range. The beam quality of the amplified pulses was within 1.3 times the diffraction limit, making possible focused intensities in the 1018 W/cm2 range.
Frank Tittel, P. Canarelli, C. Brent Dane, Thomas Hofmann, Roland Sauerbrey, Tracy Sharp-Clement, Gabor Szabo, William Wilson, P. Wisoff, Shigeru Yamaguchi
The development of scalable high power lasers in the UV-visible range and ultrashort high brightness laser sources will have significant impact in a number of key technologies. Experiments of scaling the e-beam pumped
XeF(C—>A) laser system to the 1 Joule/pulse output level at a 1 Hz repetition rate are described. Recent progress in the amplification of tunable ultrashort laser pulses in the visible spectrum, utilizing the broadband XeF(C—>A) excimer transition, is also reported.
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