By G. Jay Doster, Ph.D. and Ryan Feeler, Ph.D., Northrop Grumman Cutting Edge Optronics
Many laser applications require very high peak powers at high repetition rates. The pulses are typically generated from mode-locked laser oscillators, fiber laser oscillators, or modulated CW fiber lasers. Amplifying these pulses to useable peak powers can be challenging as the typical seed laser sources require gains of 30dB or more. In order to obtain high gains in laser amplifiers, high pump powers are required. Continuous operation at high pump powers can limit operational lifetime of the amplifiers and can fracture the gain medium in extreme circumstances. Operation of the amplifiers in quasi-CW mode allows high pump powers without the negative thermal effects seen in the CW pumped case.
Northrop Grumman Cutting Edge Optronics (NGCEO) has developed a line of laser amplifiers specifically for high-energy, quasi-CW operation. The PowerPULSE™ laser amplifiers can operate at high pump powers for pumping times on the order of milliseconds. This allows high amplification factors over longer times at lower thermal loads than is available with flash lamp pumped systems. These amplifiers have been used in a wide range of applications, including combustion diagnostics, Optical Parametric Chirped Pulse Amplification (OPCPA), and fundamental physics and chemistry experiments.
If the application allows, the pulses from the seed laser can be chopped into a series of ‘macro-pulses', each of which contains a sequence of optical pulses at the repetition rate of the seed laser.