Pulse-burst laser systems for fast Thomson scattering (invited)

Abstract

Two standard commercial flashlamp-pumped Nd:YAG (YAG denotes yttrium aluminum garnet) lasers have been upgraded to "pulse-burst" capability. Each laser produces a burst of up to 15 2 J Q-switched pulses (1064 nm) at repetition rates of 1-12.5 kHz. Variable pulse-width drive (0.15-0.39 ms) of the flashlamps is accomplished by insulated gate bipolar transistor (IGBT) switching of electrolytic capacitor banks. Direct control of the laser Pockels cell drive enables optimal pulse energy extraction, and up to four 2 J laser pulses during one flashlamp pulse. These lasers are used in the Thomson scattering plasma diagnostic system on the MST reversed-field pinch to record the dynamic evolution of the electron temperature profile and temperature fluctuations. To further these investigations, a custom pulse-burst laser system with a maximum pulse repetition rate of 250 kHz is now being commissioned.

High-Repetition-Rate Ultrafast Fiber Lasers for Material Processing

“…The low duty cycle leads to the attainable output powers which circumvents the impractical requirements for laser systems to produce high-energy (at least, at the microjoule level) pulses continuously at very high repetition rates. As a matter of fact, burst-mode laser systems have been in use for a while in niche applications such as accelerators [6], [7], combustion diagnostics [8], flow measurements in aerodynamics [9], Thomson scattering experiments [10], pulsed laser deposition [11], photoacoustic microscopy [12]. More recently, they have also been attracting attention as tools for efficient material processing [13]- [16] since it was demonstrated as a strong alternative by Marjoribanks and colleagues [17].…”

Operation and beam profiling of an up to 200 kHz pulse-burst laser for Thomson scattering

“…Thermal conduction estimates imply that a typical burst sequence is too short for thermal gradients to build up in the laser rods, while the 2-4 min laser off period between burst sequences gives enough time to completely cool the rods. 4 Measuring that the beam profile in the far field does not change over a sequence of pulses helps confirm the lack of thermally induced changes in beam focusing. A series of 2 mm thick graphite disks with different sized holes were used as a set of fixed sized apertures on the laser running at full power.…”

“…The laser discussed here is being developed as an upgrade to MST's Thomson scattering system, 4 utilizing the same beamline, collection optics, and detection systems. 5 The established systems necessitate a 1064 nm based laser, with minimum pulse energies on the order of 1.5 J.…”

3.5-GHz intra-burst repetition rate ultrafast Yb-doped fiber laser

“…This way, reasonable average powers are obtained despite the high repetition rates achieved during the burst. For a long time, burstmode operation has been applied to diverse, but niche applications [8][9][10][11][12][13][14]. This is partly because, until recently, burst-mode laser systems have relied on complex solid state lasers, with architectures that were not optimized for burst mode.…”