In this paper, we report on current developments aimed at improving the focusability of the Texas Petawatt Laser. Two
major campaigns have been commissioned that address the issue of focusability. First, we implemented a closed loop,
32 actuator bi-moprh deformable mirror (DFM) to compensate for aberrations in the optical train and second, a color
corrector lens assembly was installed that compensates for chromatic errors accumulated in broadband (>15 nm), large
aperture (>20 cm) laser systems.
We will present in detail, pre and post correction results with the DFM and describe challenges faced when one activates
a single shot, high energy closed loop system. Secondly, we will provide modeling and experimental results of our color
correction system. This is a novel approach to a problem only seen in high energy, broadband, large aperture laser
By using color correction optics we have demonstrated a 6X increase in focal intensity. With the installation of the
DFM, the rms wavefront error in the system was reduced from 2.4 waves to .131 waves, further increasing intensities
seen at focus by 1 order of magnitude.
We report on the design and construction of the Texas Petawatt Laser. This research facility will consist of two, synchronized laser systems that will be used for a wide variety of high intensity laser and high energy density science experiments. The first laser is a novel, high energy (200 J), short pulse (150 fs) petawatt-class laser that is based on hybrid, broadband optical parametric chirped pulse amplification (OPCPA) and mixed silicate and phosphate Nd:glass amplification. The second laser will provide 500 J at 527 nm (>1 kJ @1053 nm) with pulse widths selectable from 2-20 ns. Design and construction began in early 2003 and is scheduled to complete in 2007. In this report we will briefly discuss some of the important applications of this system, present the design of the laser and review some of the technology used to achieve pulse durations approaching 100 fs. Currently, the facility has been renovated for laser construction. The oscillator and stretcher are operational with the first stage of gain measured at 2×106. Output energies of 500μJ have been achieved with good near field image quality. Delivery has been taken for Nova components that will compose the main amplifier chain of the laser system.
We report initial operation of the Mercury laser with seven 4 x 6 cm S-FAP amplifier slabs pumped by four 80 kW diode arrays. The system produced up to 33.5 J single shot, 23.5 J at 5 Hz, and 10 J at 10 Hz for 20 minute runs at 1047 nm. During the initial campaign, more than 2.8 x 104 shots were accumulated on the system. The beam quality of the system was measured to be 2.8 x 6.3 times diffraction limited at 110 W of output, with 96% of the energy in a 5X diffraction limited spot. Static wavefront glass plates were used to correct for the low order distortions in the slabs due to fabrication and thermal loading. Scaling of crystal grown has begun with the first full size slab produced from large diameter growth. Using an energetics optimization code we find the beam aperture is scalable up to 20 x 30 cm and 4.2 kJ.
Optical parametric chirped pulse amplification (OPCPA) is a scalable technology for ultrashort pulse amplification. Its major advantages include design simplicity, broad bandwidth, tunability, low B-integral, high contrast, and high beam quality. OPCPA is suitable both for scaling to high peak power as well as high average power. We describe the amplification of stretched 100 fs oscillator pulses in a three-stage OPCPA system pumped by a commercial, single- longitudinal-mode, Q-switched Nd:YAG laser. The stretched pulses were centered around 1054 nm with a FWHm bandwidth of 16.5 nm and had an energy of 0.5nJ. Using our OPCPA system, we obtained an amplified pulse energy of up to 31 mJ at a 10 Hz repetition rate. The overall conversion efficiency from pump to signal is 6%, which is the highest efficiency obtained with a commercial tabletop pump laser to date. The overall conversion efficiency is limited due to the finite temporal overlap of the seed (3 ns) with respect to the duration of the pump (8.5 ns). Within the temporal window of the seed pulse the pump to signal conversion efficiency exceeds 20%. Recompression of the amplified signal was demonstrated to 310 fs, limited by the aberrations initially present in the low energy seed imparted by the pulse stretcher. The maximum gain in our OPCPA system is 6x107, obtained through single passing of 40 mm of beta- barium borate. We present data on the beam quality obtained from our system (M2=1.1). This relatively simple system replaces a significantly more complex Ti:sapphire regenerative amplifier-based CPA system used in the front end of a high energy short pulse laser. Future improvement will include obtaining shorter amplified pulses and higher average power.
We have begun building the 'Mercury' laser system as the first in a series of new generation diode-pumped solid-state lasers for inertial fusion research. Mercury will integrate three key technologies: diodes, crystals, and gas cooling, within a unique laser architecture that is scalable to kilojoule energy levels for fusion energy applications. The primary performance goals include 10 percent electrical efficiencies at 10 Hz and 100J with a 2-10 ns pulse length at 1.047 micrometers wavelength. When completed, Mercury will allow rep-rated target experiments with multiple target chambers for high energy density physics research.
We have characterized the phasematching angle, bandwidth, thermal conductivity, and d(lambda) /dT for potassium titanyl phosphate, potassium titanyl arsenate and rubidium titanyl arsenate optical parametric oscillators.
The development and operation of a kilowatt scale KD(asterisk)P second harmonic generator is described. The design utilizes a simple and compact two-plate alternating-Z configuration with a transverse thermal gradient. The calculated single pulse conversion efficiency is between 50 and 75 percent for beams whose divergence is up to 15 times the diffraction limit. Offline subaperture tests demonstrated that the effect of induced thermal gradients on conversion efficiency was less than 5 percent for optical loads expected for kilowatt operation. Full aperture tests with a 300 watt average power Nd:glass zigzag slab laser gave conversions of 35 percent.