CMOS Laser Beam Profiler

[tony.olivieri]

Hi Guys,

I’m looking for some help with a laser beam profiler program I’ve been working on. I’m using a CMOS camera from ImagingSource (DMK33UX249), 1920 x 1200 resolution, 16-bit monochrome. I’m having a hard time figuring out a couple of things.

The first issue is with the image intensity. The laser beam spot is always a completely saturated spot rather than Gaussian shaped. I would much prefer to not have any ND filters in the setup, but even with heavy attenuation filters reducing the optical power to a few uW. The image still comes up saturated. The only method that has worked so far is to apply an FFT filter. Intuition tells me this is not really a valid method to remove this saturation. How can I get this program to automatically correct its intensity levels (?) for a range of optical power levels?

The second issue I’m having is related to a specific project I’m working on which uses a modulated laser source. What would be the best way to create a type of user controlled trigger? My laser is modulated at only 10 Hz, but due to program execution time(?) images show up at random intervals. It’s not a big issue, just not very convenient to make optical adjustments in real time and grab images.

I uploaded the code I have so far, it’s functional, and I’m probably doing a lot of things wrong, so any help and recommendations would be greatly appreciated.

[Kyle97330]

I do a lot of beam profiling, working for a laser company.

When I go to this site, showing the camera specs:

https://www.theimagingsource.com/en-us/product/industrial/33u/dmk33ux249/

It says it has an "electrical trigger".  I don't have IMAQ (we use purpose-made beam profiling software, not just trying to do it on an off-the-shelf camera).  However, I would imagine that somewhere in IMAQ it should be able to set it up to use that electrical trigger to sync its frame captures.

How does your laser source modulate?  Some sources I use have a modulation input that we send a signal to, and others have internal modulation, and some of those have a modulation output.  If you have any of those, you might be able to hook it directly to your camera.

If you don't have a simple signal, you might need to add either a photodiode and a circuit to use that to trigger the camera, or add a tap on the power supply for the laser and add a circuit to detect the power ramping up to also trigger your camera.

If you don't want to or can't use the electrical trigger, then your only real option is to always set your camera's exposure time to a multiple of your laser frequency, so you always capture an integer number of full on/off cycles.  However, at 10Hz, even 1 cycle at 100 ms is not great (max of 10 FPS).

As for the intensity, cameras have 3 main ways to control it:

Exposure time

Gain (but that's usually to get more from a weak signal, which is not your problem)

Filtering (via ND filters usually, but you can also use other optics such as beam splitters or polarizers)

The camera specs you have says it can go down to 30 µs.  Have you tried setting it down that far and seeing if it still shows as saturated?

Also, may I ask if there's a specific reason you prefer not to use ND filters?  Generally, if we want to avoid filters completely, we use something like a "Nanoscan" which is a lot more specialized but can be used on much more powerful beams without filters.