THORLABS M2MS, Руководство по эксплуатации

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BP209 Series 7 Operation Instructions
Page 72
21424-D02
7.1.4 Pulsed Laser Sources
BP209 Series Beam Profilers can also be used to measure the profile of pulsed laser beams,
although the better choice for such applications is the Thorlabs BC207 Series Camera Beam
Profiler.
Pulsed laser sources with high repetition rate and short pulse duration can be measured in the
same way as a CW laser. A typical example is a femtosecond laser, having repetition rates of
up to 100 MHz and pulse durations below 100 fs.
In such case, the photo diode current amplifier due to its limited bandwidth "sees" not a pulse
train, but virtually a CW signal.
The situation is different if the repetition rate is in the order of up to tens of kHz. In order to illus-
trate how to optimally setup the Beam Profiler, below are given two examples.
Used Laser System
· Thorlabs LPS-635-FC pigtailed laser diode with adjustable collimation package
· Controller ThorIabs ITC4001 in QCW mode (f
rep
= 1kHz, t
pulse
= 100µs)
Scan Rate Setting
The scan rate can be set between 2.0 and 20 Hz, so it cannot be set equal to the pulse
repetition frequency. In the above case, if the scan rate is set to 10Hz, each 100th pulse will be
scanned. Due to the high repetition frequency, previous and following pulses will also be
displayed:
If set the scan rate in such way, that in X and Y profile the pulses move through the diagram
(i.e., so that the pulse rate slightly differs from an integer multiple of the scan rate), and activate
the max hold function function, the software will accumulate the peak intensities over a
number of subsequent pulses, and finally, the beam profile will be displayed - however, this is
the averaged profile over a number of subsequent pulses.
Note
The user should decide when the envelope shape smoothing can be considered to be finished.
Bandwidth Setting