|The 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.|
SR400 Gated Photon Counter
The 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
The SR400 has two independent channels that can count at rates up to 200 MHz. Different counting modes allow you to count for a fixed amount of time, until a certain number of counts have been received, or for a fixed number of triggers. Each counting channel has its own gate generator providing counting gates as short as 5 ns or as long as 1 s. The gates can be set in a fixed position relative to the trigger signal, or scanned to measure lifetimes or recover
The actual inputs to the counters can be viewed as NIM level pulses from the discriminator outputs on the front panel. The discriminated pulses are negative going from 0 to -0.7 V. The DISC outputs are very useful when adjusting discriminator thresholds or gate timing.
SR400 Block Diagram
Signal Inputs and Discriminators
Both analog signal inputs
Discriminators are provided for each channel with a selectable threshold from -300 mV to +300 mV in 0.2 mV steps.
The SR400 may be programmed to cycle from 1 to 2000 count periods in a single scan. At the end of the programmed scan, the counters may be stopped or the scan may be restarted. Consecutive count periods are separated by a "Dwell Time" which can be set from 2 ms to 60 s. During the Dwell Time, counting is disabled and data may be transferred or external parameters may be changed. The dwell output provides a TTL signal which is high during the dwell time. This can be convenient for interfacing other instruments used in the experiment.
The front panel can display counts up to
Built-in RS-232 and GPIB interfaces provide a convenient means of controlling the instrument and retrieving data. While the SR400 is scanning, each of the count values for the A and B counters are stored in a 2000 point internal buffer. This buffer can be transferred on a point-by-point basis, or dumped all at once through either interface.