Soluciones y Tecnologías de Control Embebido S.A.P.I. de C.V.
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Passive Q-Switch Laser Connection Example
In solid state pulsed lasers with passive Q-Switch optical shutters, we do not have precise
control of the laser emission moment. In some models of commercial lasers, they provide a signal
of synchronism with respect to the firing of the flash lamp, but in any case the very nature of the
passive Q-Switch shutter inserts some type of variability in the instant of emission of the laser
pulse, variability that will depend from the pumping energy of the lamp and even from
environmental factors such as humidity and temperature. In this case, a solution may be to detect
with a high-speed photodiode module the emission of the laser pulse, and use this signal to trigger
the spectrometer. It should be noted that the spectrometer must be one with a high response
speed between the reception of the trigger signal and the entry into the integration zone of the
image sensor they have. As a general rule, spectrometers with high response speed or low latency
between the reception of the trigger and the capture of the spectrum are those that have an
image sensor, almost always of the charge coupled type (CCD) with shutter-electronic. Therefore,
before selecting a spectrometer for this application, ask the supplier if the used sensor enters the
integration zone immediately after receiving the trigger signal and it is not only enough to know
the value of said time, but also if it is constant between catch. The following figure shows an
assembly to trigger an optical spectrometer using the DG-3O1I-17 from the analog signal of a
PDA10A type photodiode module from the manufacturer Thorlabs.
Fig. 37. Spectrometer triggering from the optical detection of a laser pulse
The laser pulses with Q-Switch are of short duration, in the order of units or tens of nanoseconds,
it will also be the output of the photodiode module, so it can be considered virtually as a very
