A study of flow characteristics of a high repetition rate dye laser gain medium

The gain medium of a high repetition rate liquid dye laser is made to flow at a sufficiently high velocity through the dye cell in order to minimize the thermal inhomogeneity. In this paper, temperature contours as a function of distance from the pump beam entrance dye cell window wall at various flow velocities in the laminar and turbulent region of gain medium flow were evaluated using computational fluid dynamics (CFD). Appreciable temperature gradients subsist at low Reynolds numbers due to inefficient heat transfer from the gain medium. However, at high Reynolds numbers >6000, the substantial effects of local density turbulent fluctuations degrade the optical quality of the gain medium. These computational studies were used to elucidate the characteristics of observed spectral fluctuations of a dye laser as a function of the Reynolds number. (paper)