laser illumination system

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ph1jrh

Newly Enlightened
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Oct 15, 2010
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Hello.

As part of a science project i would like to illuminate a fast rotating sample using laser illumination. However, laser illumination suffers from speckle, especially when viewed using a CCD camera.

I want to use a laser so i have monochromatic light, so i can get intereference effects from the surface i am illuminating. However, lasers give speckle.
  • 🙁
DAMN DAMN.

You can get things to remove speckle from laser light:

http://www.optotune.com/index.php?option=com_content&task=view&id=72&Itemid=61

...however, these are beyond my budget.

Does anyone know how to make a cheap laser illumination set-up which is free from speckle...
Any and all help is most welcome....
 
Can you say what it is you are attempting to measure? As far as your budget, how much is the optotune device and where does that fall relative to your budget? Do you care to mention what level class this is and where?
 
The sample a polymer in an organic solvent (think nail varnish/polish) on a fast (3000 rpm - think Dremmel) spinning flat surface/disc.
I need a very bright illumination system which is monochromatic..hence laser light.
Budget = <$250 (Optotune device = $1500 +)
Class of laser = not important to me, as long as it is bright enough. All laser will be used by laser safety trained people
Where = in a lab setting.

Have though of possibly using a modulation to the drive circuitry to de-tune the laser slightly, making the spectral line broader.

Any help welcome.
 
Are the defects in the nanometer range then? We have had to deal with speckle on some of our systems but typically it is because we do not want a user to see it not because it is an issue in a measurement system. The same coherency that gives you the ability to measure defects unfortunately highlights the imperfections in your source creating the speckle. Unless you are measuring defects that are less than half the wavelength of the laser source it should just be noise shouldn't it?
 
We are measuring film thicnkesses of the order of nanometers. In particular the film thinning, as the solvent leaves. We can detect changes in thickness of the film, of the order of 1 nanometer. I hope this helps.
 
This well outside of my level of experience so I defered to our OE's. They blathered on about the required wavelengths and resolution until I interrupted with your budget limitation. "Add three zeros" was the response I got. One nanometer is really small!

Sorry I couldn't be of any real help. If I come across something I'll post a link otherwise good luck.
 
Thanks anyway. The film thickness monitoring works by interference effects. If you shine light at a liquid film on a reflecting surface/mirror (or in my case solvent+polymer on a silicon wafer) you get reflections from the air/liquid surface and reflections from the liquid/solid interface. These two reflections interfere, and satisfy Bragg law for diffraction for constructive interference. As the films thins it passes through maxima (constructive interference) and minima (destructive interference) and the film appears bright or dark. The change in thickness between two bright points (in time) is equal to wavelength/3 = delta_D = 173nm of for a 520nm light source.

I have found this "mechanical" diffuser system which could be modified: http://www.jetsetmodels.info/pics/basic_35mm_dof.pdf

I think you basically need to move a diffuser about at high speed, faster than your shutter speeds.,
 
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