Utility of a tunable dye laser, wherein the lasing medium comprises a dye material in solution, to isotope separation has been recognized as, for example, in U.S. Pat. No. 3,772,519, incorporated herein by reference and assigned to the same assignee as the present application. For continuous operation of an isotope separation facility for uranium enrichment using the same or similar techniques as described there, it is desired to have pulsed beams of high intensity laser radiation operating on a generally continuous basis. This in turn requires that the laser systems operating to provide such beams be capable of operation for prolonged periods without degradation in beam quality or intensity. One source of degradation in laser performance over extended periods is associated with the windows that operate as a containment for the flowing dye medium and through which the excitation energy used in amplification is applied. Degradation at these points can result from solarization of the window material, i.e. gradual darkening or loss of transmissivity of the window, as well as a decomposition of the dye material on the inner surface of the window over time which would also reduce the window transmissivity and contribute to a loss of efficiency and promote unwanted heating. The containment walls will also produce a boundary layer effect leading to inefficient heat removal in the flowing medium.
It has been suggested in order to overcome this and other difficulties in laser amplifiers to employ a totally free jet in which there is no boundary layer between the jet and a containment vessel in the region of laser amplification.