|
The purpose of this thesis is to make a new computer controlled data acquisition system to measure the picosecond (ps) laser pulse energy and move the sample. Using the system built last year, when we perform measurements, we can monitor each individual pulse’s energy and exclude the data obtained with the pulses whose energies lie outside the energy window. This helps to reduce the noise of the data. In this newly designed system, we introduce the autocorrelation function to additionally monitor the input picosecond pulse duration. This further reduces the noise by ignoring the data obtained with too long or too short pulses.
To measure ps pulse laser energy, we choose the EG&G UV-444BQ photodiode with a series of circuits which sequentially read the pulse energy, convert the signal phase by , and hold the peak voltage for a long time (10 seconds). When the peak voltage corresponds to the laser pulse energy, by peaking and holding it, we can easily pick it up using a kilohertz analog-to-digital (A/D) converter which is commercially available.
The hardware control program is written with National Instruments automatic control software “LabVIEW”. Because this program operates under the Windows interface, it is much friendlier for users than the Pascal automatic control system under DOS interface that has been used in the past in our laboratory. When writing the Pascal program formerly, we need to write a lot of codes, including the assembly ones, to control the data acquisition and sample motion actions. So the programmer must have sufficient skill, experience and carefulness to deal with this program. With LabVIEW design program, however, we can perceptively write, modify and operate the program all by graphic codes.
We test our system’s performance with ps Z-scan experiments on a standard sample (methyl blue). In the measurements, the autocorrelation is incorporated to monitor the pulse width.
|