Since Krupke et.al. proposed and demonstrated pumping alkali atoms using diode lasers in
2003, there has been lot of interest in the diode pumped alkali laser (DPAL) systems. Several
researchers have been able to scale the DPAL system to powers in the tens of watts. We have
conducted a systems-level, weight-scaling study of a notional medium power, CW DPAL system.
Three different modes of operation are considered: (i) very high pressure operation (over 25
atmospheres of He) in which the absorption and emission lines of the alkali atoms are broadened
sufficiently to allow for efficient pumping with off-the-shelf diodes that have line width of 2 to 3
nm, (ii) intermediate pressure regime (~ 5 atmospheres) that requires diodes that are line narrowed
to ~0.4 nm, and (iii) low pressure operation (~ 1 atmosphere) that requires diodes that are line
narrowed to < 0.1 nm for efficient pumping of pump radiation into the alkali vapor. In the latter two
cases some amount of methane, ethane, or some other gas would be needed to mix the two upper
states rapidly; while in the first case, helium is used to broaden the transition and to mix the upper
states. We have considered closed-cycle transverse flowing systems with the transverse length
limited by medium inhomogeneity caused by heat deposition into the gas. Weight models have been
developed for each of the following sub-systems: Pump Diodes, Fluid Flow System, Thermal
Management System, Optics and Diagnostics System, Instrumentation & Control System, and
Electrical Power system. The results of our weight estimates for a notional 100 kW DPAL system
are presented.
The Brillouin-enhanced four-wave mixing (BEFWM) technique for phase conjugation in high-power laser systems is presented. The technique represents a form of nearly degenerate four-wave mixing in which the four beams are coupled acoustically through Brillouin nonlinearity. Emphasis is placed on the case of the Brillouin geometry where the second pump beam is downshifted by the acoustic frequency from the first pump. A 1D steady-state model has been developed which takes into account the limitation of the reflectivity of the BEFWM process due to the presence of a small component of the second pump beam with the same polarization as the first pump beam. In addition, 3D wave optics code have been developed for calculating the conjugation fidelity under less than ideal conditions such as misalignment of the pump beams, the two pump beams not being perfect conjugates of each other, etc.
The RF Linear Accelerator Free Electron Laser is usually operated in the oscillator mode. For high power operation, a ring resonator configuration with grazing angle incidence optics is the preferred choice. In this paper, we describe the modeling of such an oscillator configuration using full wave optics. The steady state mode structure of the resonator is obtained using Fox-Li type of calculation. We start with a gaussian field and propagate this field through the wiggler and the optical components of the resonator. The field at the end of one iteration through the resonator is compared with the field at the start of the iteration. This process is repeated until the field shape and the cavity power levels reach steady state reproducibility to within a couple of percent. The FEL interaction is modeled by tracking the motion of thousands of electrons through the wiggler and averaging their energy loss. Betatron motion of the electrons is taken into account as are any field and misalignment errors in the fabrication of the wiggler. We have used this numerical model to investigate the effects of (i) misalignment of mirrors, (ii) aberration of the mirrors, (iii) the efficacy of compensatory misalignment techniques, and (iv) the dependence of the performance of the FEL on the outcoupling fraction.
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