Electronics > Projects, Designs, and Technical Stuff
Can you excite a laser with a waveform different than square or DC?
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zdelarosa00:
I was looking at LIDAR sensors datasheets and manuals, and apparently they all use square pulse trains to fire their lasers.
According to this: ("Airborne topographic mapping lidars generally use 1064 nm diode pumped YAG lasers, while bathymetric (underwater depth research) systems generally use 532 nm frequency doubled diode pumped YAG lasers because 532 nm penetrates water with much less attenuation than does 1064 nm. Laser settings include the laser repetition rate (which controls the data collection speed). Pulse length is generally an attribute of the laser cavity length, the number of passes required through the gain material (YAG, YLF, etc.), and Q-switch (pulsing) speed. Better target resolution is achieved with shorter pulses, provided the lidar receiver detectors and electronics have sufficient bandwidth.[4]" https://en.wikipedia.org/wiki/Lidar#Components).... I understand that you get more distance range from firing a short train of pulses than powering a continuous beam.

But the main question is:
Do commercial laser diodes permit amplitude/brightness changes?
I exactly would like to understand if dimming is possible or the material itself and construction set a minimum threshold for turning it on and of course a maximum voltage amplitude, so the light can't effectively dim of change brightness, and therefore can't output a light wave different thatn square or DC.
Maybe they probably can but it's a very small variation.  :-//
coppercone2:
if it does not use a resonance burst then yes, otherwise you would need to change the system.

Benta:

--- Quote from: zdelarosa00 on December 21, 2018, 02:53:51 pm ---
But the main question is:
Do commercial laser diodes permit amplitude/brightness changes?


--- End quote ---

Normally not, if you drop the current too far, they stop "lasering". There's a reason for the photodiode for optical feedback in the devices.
zdelarosa00:
Apparently this is a fairly common laser diode datasheet. And they don't specify a minimum where voltage and current is.

Do the graphs say something else? Or is the characterization of the semiconductor for performance check under not so normal conditions?
james_s:
The output power does vary with current, to a point. Some types of lasers can operate over a wider range than others. With the early red laser diodes the gap between where lasing begins and catastrophic optical damage was quite narrow, hence the need for a feedback photodiode and careful current control. Many more modern lasers can operate over a much wider range. For example I have a 445nm blue laser diode that produces a useful beam from under 100mA all the up to over 1A where it produces ~1W of optical power.

Diode pumped solid state lasers tend to have a narrower range of operation.
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