Q. Can the phase controller ROM be programmed to provide a
sawtooth waveform output?
A Virtually any output voltage profile can be programmed into the
ROM. This signal is then read out and converted by the DAC into a
corresponding d.c. voltage between 0 and 2 volts max.
Q. Why do you have four PSD channels when two should be adequate?
A For a simple first and second derivative measurement system two
channels are usually all that is required. However with an
additional two PSD channels the measurement system can be made more
robust. For example in gas species spectroscopy the additional PSD
channels can be used to monitor a reference gas cell containing the
species of interest, these signals can then be used to lock the
laser line at the correct wavelength. These additional channels
allow you to use Feedback Control.
Q. I have heard of using the f and 2f signals but why would I
want to use the 3f derived signal?
A To actively lock a laser wavelength onto an absorption feature a
zero crossing monatomic signal is required. Traditionally this is
achieved by monitoring the first derivative signal (f).However when
a semiconductor laser is used the first derivative signal is usually
superimposed upon a slanting dc background signal derived from the
modulation characteristics of the laser itself. No zero cross over
is produced. If a 3f signal is used this slanted dc characteristic
is virtually eliminated and simpler active locking made possible.
Q. Can I change the modulation frequency of the phase controller
board?
A. Yes, simply by changing the frequency of the crystal to reduce
the fundamental frequency. If you wish to modulate at higher
frequencies this may be be possible albeit with the loss of phase
resolution.
Q. If I did this would I have to change the PSD filter values?
A. Yes, we can do this at AOS, for a small charge during
manufacture or we can supply the board with minimum components and a
design brief.
Q. What are the power supply requirement of the phase controller,
laser driver and PSD boards?
A. The phase controller board and the laser driver board run from
+5volts. As with all laser driver circuits a good quality low-ripple
supply is recommended. The PSD board requires +/-12 volts. This can
either be provided by the laser driver board via feed through
connectors or via an external power supply. N.B. the low noise dual
rail supply on the laser driver board requires a split rail d.c.
input although this can be provided by a switching mode supply.
Q. Does the laser need to run off +5volts?
A. No, a separate lower voltage supply can be used. |
