A high-frequency train of 5–100-ps pulses (picket fence) is proposed to improve significantly the third-harmonic frequency conversion of Nd:glass lasers that are used to generate high-contrast-shaped pulses for inertial confinement fusion (ICF) targets. High conversion efficiency of the low-power foot of a shaped ICF pulse is obtained by use of a low duty cycle, multi-gigahertz train of ~20-ps pulses with high peak power. Even with less than 10% duty cycle, continuous illumination is maintained on the target by a combination of temporal broadening schemes. The picket fence approach is analyzed, and the practical limits are identified as applied to the National Ignition Facility laser. It is found that the higher conversion efficiency allows ~40% more third-harmonic energy to be delivered to the target, potentially enabling the larger drive needed for high-yield ICF target designs. In addition, the frequency conversion efficiency of these short pulses saturates much more readily, which reduces the transfer of fluctuations at the fundamental and thus greatly improves the power stability of the third harmonic.
© 2000 Optical Society of America
(190.2620) Nonlinear optics : Harmonic generation and mixing
(320.5540) Ultrafast optics : Pulse shaping
(320.7090) Ultrafast optics : Ultrafast lasers
(320.7110) Ultrafast optics : Ultrafast nonlinear optics
(350.2660) Other areas of optics : Fusion
Joshua E. Rothenberg, "Ultrafast Picket Fence Pulse Trains to Enhance Frequency Conversion of Shaped Inertial Confinement Fusion Laser Pulses," Appl. Opt. 39, 6931-6938 (2000)