Subnanosecond single-beam thresholding and a high-contrast, high-gain optical AND gate are demonstrated using a nonlinear Fabry-Perot InGaAsP/InP laser amplifier. These devices switch on or off in less than a nanosecond, dissipating only femtojoules of optical input energy. They have large gain (10-20dB) and are operated using diode laser sources. The switching dynamics are theoretically modeled. Potential applications of arrays of these devices for parallel signal processing and computing are discussed.