William Angerer - Department of Physics and Astronomy - University ...

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gain, low noise, head-on photomultiplier tube. The photocathode is made of GaAs.
which has a quantum efficiency of "V 14% over the range of our SHG spectroscopic
measurements l.
3.2 Data Acquisition
The signals from the sample and reference photomultiplier tubes were sent directly
to a pair of Stanford Research Systems SR530 lock-in amplifiers. The data from the
lock-in amplifiers were transfered through a GPIB cable to a National Instruments
AT-GPIB/TNT GPIB board in a 100 MHz Dell computer with a Pentium processor.
I wrote a Quick Basic 4.5 program to graphically display, analyze, and store the
data. All experiments in this thesis, with the exception of the photoluminescence
experiment. acquire data in the same manner as the nonlinear spectroscopy data
acquisition scheme.
Prior to measuring the signals from the sample and quartz, a background measurement
from both the sample and reference lines was made with the laser blocked.
The appropriate background measurements were subtracted from the sample and reference
signals, and a normalized signal was reported as the ratio of the sample to
reference signals. In a typical nonlinear spectroscopic measurement, the lock-in amplifiers
were set to a 300 ms time constant and data was acquired every second for
I The R943-02 has a quantum efficiency of '" 15% at 350 nm which monotonically decreases to
'" 13% at 500 nm.
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