Laser frequency doubling in the presence of small-scale beam breakup

Frequency multiplication of intense laser pulses in narrow acceptance angle crystals is commonly accomplished with large conversion efficiency. However, the conversion efficiency can be seriously affected by degradation of the laser pulse, such as occurs when small-scale intensity fluctuations exponentiate due to nonlinear refractive effects within the laser. We present evidence that beam breakup such as this can cause a significant fraction of the laser energy to lie outside the acceptance angle of the crystal, thus diminishing conversion efficiency.