Abstract: A transverse flow uniform droplet generator and method for its use. The droplet generator, such as is used with a gas laser system, produces singlet oxygen from a flow of droplets of liquid basic hydrogen peroxide (BHP) reacting with a transverse a flow of He/Cl.sub.2 gas mixture. The resulting flow of singlet oxygen travels in the same direction as the He/Cl.sub.2 gas mixture and the unreacted BHP is collected on the opposite of the reaction volume from which it enters. Very uniformly-size BEP droplets are formed by an injector which specific mechanical resonance characteristics and the flow of the BHP and the gas mixture in the generator volume is also carefully controlled.