Rationale for supersonic pulsed chemical lasers and problem areas related to design and use of associated reagent premixers are described. An analytical model of reagent mixing and reaction for evaluation of 'prereaction' and mixing characteristics of high enthalpy H2-F2-diluent flows is formulated and programmed for computer solution. The code is used to evaluate parametric dependence of prereaction level and required mixing length on principal parameters defining candidate premixer flows. Possible flow choking and subsequent detonation in the mixing region resulting from reacting flow transients following a fast laser-reaction pulse are examined, both by defining conditions under which choking by chemical heat addition and/or Chapman-Jouguet detonations are energetically allowed, and by using a simplified reacting flow model to estimate kinetic limitations on probable occurrence of such disturbances. (Modified author abstract).