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Photon Counter
SR400 Gated photon counter

SR400 ... from $5350
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SR400 Photon Counter

Front Panel

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SR400 Photon Counter

Rear Panel

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  • Two independent channels
  • Count rates to 200 MHz
  • 5 ns pulse-pair resolution
  • Gated and continuous modes
  • Gate scanning
  • Built-in discriminators
  • Gate and discriminator outputs
  • GPIB and RS-232 interfaces
  • Overview
    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.
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    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 pile-up correction can all be performed easily with the SR400.

    Counters

    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 time-varying waveforms.

    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.

    Block Diagram

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    SR400 Photon Counter

    SR400 Block Diagram

    Signal Inputs and Discriminators

    Both analog signal inputs (A and B) are internally terminated into 50 Ω. The inputs accept signals between ±300 mV and are protected to ±5 VDC. Each input is followed by a DC to 300 MHz amplifier, allowing detection of pulses as small as 10 mV. If additional sensitivity is required, a remote preamplifier (like the SR445A) can be used.

    Discriminators are provided for each channel with a selectable threshold from -300 mV to +300 mV in 0.2 mV steps. Pulse-pair resolution is 5 ns, and pulses of either polarity may be detected. Each threshold may be programmed to scan in either direction with selectable step size. This can provide a pulse height analysis (PHA) output and is useful for choosing photomultiplier tube bias or discriminator levels.

    Count Periods

    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.

    Outputs

    The front panel can display counts up to 109. Results from both counters can be displayed individually or combined as A-B or A+B. A front-panel D/A output provides an analog signal proportional to A, B, A-B, or A+B, depending on the counting mode. The scale may be logarithmic (1V/decade) or linear.

    Computer Interfaces

    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.

    Phone:(408)744-9040 • info@thinkSRS.comwww.thinkSRS.com