Changes

A fast light source operating in an environment with little background is necessary for the tests described here. The challenge is in preventing light leaks in this chamber despite the need for access ports, patching wires through walls and installing sensor and temperature control modules that must interface with the outside. The design, construction, and test of a dark chamber that meets these requirements, as well as approaches to data acquisition are discussed here.

A fast light source operating in an environment with little background is necessary for the tests described here. The challenge is in preventing light leaks in this chamber despite the need for access ports, patching wires through walls and installing sensor and temperature control modules that must interface with the outside. The design, construction, and test of a dark chamber that meets these requirements, as well as approaches to data acquisition are discussed here.

= Dark Box Construction =

= Dark Box Construction =

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== Light Pulser ==

== Light Pulser ==

A pulser circuit was designed with a pulse height controlled by the amplitude of a step function from a function generator. The pulser differentiates the step function signal and therefore can create pulses as narrow as the rising edge of the step function. Above a saturation point, the pulse broadens to a maximum of 6 ns. The adjacent figure shows the pulser circuit that drives the LED. The LED has some finite rise time and sometimes a very long decay tail. This response function convolves the pulser signal so the speed of the combined system has to be analyzed for each LED type and evaluated for the use of photon detector characterization.

A pulser circuit was designed with a pulse height controlled by the amplitude of a step function from a function generator. The pulser differentiates the step function signal and therefore can create pulses as narrow as the rising edge of the step function. Above a saturation point, the pulse broadens to a maximum of 6 ns. The adjacent figure shows the pulser circuit that drives the LED. The LED has some finite rise time and sometimes a very long decay tail. This response function convolves the pulser signal so the speed of the combined system has to be analyzed for each LED type and evaluated for the use of photon detector characterization.

=== Choice of Light Source ===

=== Choice of Light Source ===

By the time more detailed studies of the SSPM-06 were initiated, a fast LED very close the the mean emission wavelength of the BCF-20 was found. This was the Agilent (Avago Technologies) HLMP-CE30-QTC00. Its pulse shows a small tail in the light output that lasts for about 100ns, but this is fast enough to be contained in the 100ns integration gate used for these tests.

By the time more detailed studies of the SSPM-06 were initiated, a fast LED very close the the mean emission wavelength of the BCF-20 was found. This was the Agilent (Avago Technologies) HLMP-CE30-QTC00. Its pulse shows a small tail in the light output that lasts for about 100ns, but this is fast enough to be contained in the 100ns integration gate used for these tests.

= Data Acquisition =

= Data Acquisition =

Aside from the convenience of being able to collect usable results within hours instead of a day, this speedup also minimized the problem of systematic drifts that occur during long runs. It was found that the higher statistics obtained during extended runs would sometimes be offset by the blurring of peaks due to slow drifts in the gain and pedestal.  Whether due to environmental variations over the course of a day or electronic effects, these drifts smeared the histograms, most of which already had a very faint sign of resolved photon peaks. So, faster data acquisition also meant reducing the effects of these drifts.

Aside from the convenience of being able to collect usable results within hours instead of a day, this speedup also minimized the problem of systematic drifts that occur during long runs. It was found that the higher statistics obtained during extended runs would sometimes be offset by the blurring of peaks due to slow drifts in the gain and pedestal.  Whether due to environmental variations over the course of a day or electronic effects, these drifts smeared the histograms, most of which already had a very faint sign of resolved photon peaks. So, faster data acquisition also meant reducing the effects of these drifts.

= Test and Calibration =

= Test and Calibration =