Advanced Beam Laboratory

Overview

Colorado State University Petawatt-Class Laser is an ultra-short pulse Ti:sapphire laser system that produces ultrahigh-contrast λ = 400 nm femtosecond pulses of up to 10 J, obtained by frequency doubling 800 nm pulses of 45 fs duration. An intensity of 6.5x10²¹ W/cm2 is obtained focusing the beam with an f/2 parabola. Up to a maximum of 26 J are available at the fundamental wavelength with degraded contrast. A new long focal length f/25 beamline was commissioned in August 2020 and is available to users. Both beamlines can be operated with high contrast = 400nm or with the fundamental. The beam/pulse parameters presently offered by the laser are summarized in the Laser Modes table.

Target Areas

The facility includes a target chamber 1.2m in diameter shown in Figure 2. There are NW 200 and NW 100 located on the equator. A motorized target holder system designed to hold numerous targets and an accurate target positioning system are available. A Solid Works™ generated parasolid model of the target chamber can be downloaded here.

A suite of plasma diagnostics instrumentation is available.
These include:

Plasma Diagnostics instrumentation

A suite of plasma diagnostics instrumentation is available. These include:

• X-ray detection
  • Von Hamos crystal spectrometer operating with a 4cm radius of curvature mica crystal covering the 7 keV to 13 keV spectral region
  • Filtered silicon photodiode array; filters are available with cut-off between 1 keV and 15 keV
  • Step wedge spectrometer
• Ion detection
  • Thomson parabola spectrometer with MCP/CCD detector
• Neutron detection
  • Array of four scintillator/photomultiplier neutron detectors
  • Bubble detectors

A schematic diagram of the laser is shown in Figure 1. It consists of a conventional Ti:Sa front end that delivers λ=800 nm pulses into a chain of three high power Ti:Sa amplification stages pumped by Nd:YAG slab amplifiers. The 250 mJ output of this laser front end is further amplified in three multi-pass Ti:Sa amplifiers pumped by the frequency doubled output of eight compact flash lamp-pumped high energy Nd:glass slab amplifiers, developed at CSU. The slab geometry has long been recognized as a way to significantly reduce the limitations in repetition rate inherent to the more commonly used rod geometry. These pump laser allows Ti:sapphire system operation at a repetition rate of up to 3.3 Hz in burst mode. The beam propagates in a zig-zag path in the gain medium aided by total internal reflection in the polished wall of the slabs eliminating first-order thermal and stress-induced focusing, and also reducing stress-induced birefringence.

Each slab amplifier generates pulses with ~18 J energy and 15 ns duration at 1053 nm. The rms pulse energy fluctuation for 1053nm slab pump laser is ~1%. The amplified beams are frequency doubled by LBO crystals to generate 11 J pulses at 527 nm. The eight slab amplifier arms produce a total 527 nm pump energy of 88 J, with a uniform nearly flat-top beam profile this is used to pump the three main Ti:Sa amplifiers. The amplifier chain generates 800 nm pulses of up to 37 J energy before compression. A gold grating compressor compresses these pulses into pulses of up to 26 J energy with duration as shot as 30 fs. These pulses are frequency doubled to generate the ultrahigh contrast 400 nm pulses that constitute the normal mode of operation.