A 100 W Green Laser for Photoinjection of GaAs Photoemission Guns

For synchronous photoinjection of GaAs photoemission guns, a high-average-power green laser light source with an RF-pulse repetition rate in the range of 0.5 to 3 GHz is required to advance fundamental accelerator technology and its application to nuclear physics scientific research. The efficiency of GaAs photocathodes degrade over time. In order to maintain a constant photoemission, the photoinjector laser output power has to be increased. A 100-W average powergreen laser could provide uninterrupted photoemission for up to 4 days. Q-Peak proposes to develop a frequency doubled hybrid laser consisting of fiber and bulk lasers. The system would employ a simplified technique of generating synchronized, ps-duration pulses compared to traditional mode-locking scheme. At high-average-output power and high repetition rate, the fiber lasers offer advantage over bulk laser due to their ease of thermal management and alignment insensitive nature. However at high energy per pulse regime the fiber laser suffers from nonlinearity resulting in spectral broadening. The fiber-laser portion of the system would provide high-gain amplification of the pulses to energy levels below that where nonlinear effects in the fiber lead to undesirable pulse-distortion. The bulk laser component would then provide sufficient, distortion-free amplification to reach the desired peak and average-power levels. In our proposal, we are combing best of both fibers and bulk nature of the lasers to obtain 100 W of green power. Commercial Applications and Other Benefits: Such a laser fulfills an important near term need as a source used in photoinjector applications for linear accelerators and free electron lasers. Other than being used in the photoinjector for a GaAs photoemission gun, the laser also finds its application in the Compton polarimetry and electro-cooling in the Relativistic Heavy Ion Collider (RHIC). Other applications of the basic technology would be in the areas of time-resolved spectroscopy, terahertz generation, and materials processing. Accelerators are also used as versatile x ray sources for a wide range of applications, such as biochemistry, condensed matter, materials science and diagnostic medicine. Advances in fundamental accelerator technology may allow accelerators for these purposes to be built with greater capability while being more compact and less expensive.