The Stanford Research SR400 Dual-Channel Gated Photon Counter offers a convenient, integrated approach to photon counting that avoids the complexity and expense of older counting systems. No longer is it necessary to mix and match amplifiers, discriminators, gate generators and counters. The SR400 combines all these modules into a single, integrated, microprocessor-controlled instrument. Complex measurement tasks such as background subtraction, synchronous detection, source compensation, and pile-up correction can all be performed easily with the SR400.