COMET Laser System
(Compact Multipulse Terawatt)
The COMET laser system is a completely separate laser system from The USP and JanUSP laser systems. COMET laser system consists of a single Coherent Tsunami Ti:Sapphire oscillator that supplies seed pulses to two independent Nd:phosphate-doped glass amplifiers. When the COMET system fires, it delivers a powerful one-two punch of 1054 nm light energy onto a target system. The first burst in a COMET firing is the "long-duration pulse", typically 600 psec to 1nsec FWHM duration and up to 16.5 Joules of light energy. Then a controlled number of nsec later, the "short-duration pulse" is emitted, typically 7- 7.5 Joules of 1054 nm light in 500 fsec.
The one-two light punch out of the COMET laser system starts with a Coherent Tsunami Ti:Sapphire oscillator that maintains an intracavity pulse train of 100 fsec broad-band optical pulses 9 ns apart in time and of 1054 nm center wavelength (instead of the more common 800 nm wavelength for Ti:Sapphire). A single seed pulse is switched out of the Ti:Sapphire oscillator pulse train.
The 100 fsec broadband seed pulse from the oscillator is routed through a grating pair pulse stretcher, which stretches out the seed pulse's duration some 10,000 times to 1ns and proportionally drops its peak amplitude by the same factor. Some of this stretched duration, diminished amplitude seed pulse is picked off and run through a rod geometry Nd:phosphate doped glass amplifier, which for full power shots produces 16.5 Joules of 1054 nm light and somewhat shortens the pulse duration to typically .8 ns or so. This amplified light pulse is directed into the target, as is the "long-duration pulse", typically 600 psec to 1nsec FWHM duration and up to 16.5 Joules of light energy.
The rest of the stretched duration, diminished amplitude seed pulse is controllably delayed several nsec and then run through a different rod geometry Nd:phosphate doped glass amplifier, which for full power shots produces 7 Joules of 1054 nm light and somewhat shortens the pulse duration to typically 0.8 ns or so. This amplified light pulse is directed into a grating pulse compressor inside a vacuum chamber, and from there to the target as the "short-duration pulse", typically 500 fsec FWHM duration and up to 7 Joules of light energy.
Each of the long-duration and the short-duration arms of the COMET laser system is a chirped pulse amplifier (CPA) configuration.
The output of each arm of the COMET laser system has been carefully adjusted to minimize the amount of "pedestal" (temporal wing structure above which the laser output pulse rises ) to about 1.0E-07 of the peak pulse power. Furthermore the "pre-pulse" or contaminant leakage light from amplification of the mostly blocked next seed pulse in the oscillator train, has been minimized as well (1.0E-09). Both measures were originally taken while COMET was being considered for USP-style thin foil solid density experiments, where any pre-pulse or pedestal leakage would greatly complicate the interpretation of the experimental results.
For more details see http://www.llnl.gov/str/Dunn.html
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