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Science Forum Index » Optics Forum » Cheap USB cam for beam diameter measurement?
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| Bas |
 Posted: Wed Nov 05, 2003 10:06 am |
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Guest
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Hello group,
i want to measure laser beam diameters and plan on doing so with a
cheap USB webcam (lens removed of course and with a strong ND filter).
Does anybody have experience with this?
I tried with a CCD camera, but i fear that with the conversion to
TV-signal and the subsequent frame grabbing you mess up the resolution
along the line of pixels. Am i right that with a webcam the pixels on
the (CMOS?) chip correspond one to one to the pixels on the screen?
And do these camera's corrupt the image with compression? Any advice
on models to buy or to avoid is welcome.
Thanks in advance,
Bas |
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| Detector195 |
| Posted: Wed Nov 05, 2003 1:48 pm |
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Guest
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bassw@hotmail.com (Bas) wrote in message news:<8fe46d4f.0311050706.71919032@posting.google.com>...
Quote: Hello group,
i want to measure laser beam diameters and plan on doing so with a
cheap USB webcam (lens removed of course and with a strong ND filter).
Does anybody have experience with this?
I tried with a CCD camera, but i fear that with the conversion to
TV-signal and the subsequent frame grabbing you mess up the resolution
along the line of pixels. Am i right that with a webcam the pixels on
the (CMOS?) chip correspond one to one to the pixels on the screen?
And do these camera's corrupt the image with compression? Any advice
on models to buy or to avoid is welcome.
Thanks in advance,
Bas
I don't know about actual brands, but I do know some things to watch
out for. Many CCD cameras feed the image through some digital signal
processing. This is even true of cameras that produce analog output.
There are algorithms for things such as contrast enhancement, which
would be exactly what you don't want for your application.
It is worth looking for a camera vendor that will actually tell you
what processing is applied to the image, and perhaps even tell you how
to turn it off. |
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| AES/newspost |
| Posted: Wed Nov 05, 2003 4:29 pm |
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Guest
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In article <6213f73a.0311051048.662d612a@posting.google.com>,
Detector195@yahoo.com (Detector195) wrote:
Quote: bassw@hotmail.com (Bas) wrote in message
news:<8fe46d4f.0311050706.71919032@posting.google.com>...
Hello group,
i want to measure laser beam diameters and plan on doing so with a
cheap USB webcam (lens removed of course and with a strong ND filter).
Does anybody have experience with this?
I tried with a CCD camera, but i fear that with the conversion to
TV-signal and the subsequent frame grabbing you mess up the resolution
along the line of pixels. Am i right that with a webcam the pixels on
the (CMOS?) chip correspond one to one to the pixels on the screen?
And do these camera's corrupt the image with compression? Any advice
on models to buy or to avoid is welcome.
Thanks in advance,
Bas
I don't know about actual brands, but I do know some things to watch
out for. Many CCD cameras feed the image through some digital signal
processing. This is even true of cameras that produce analog output.
There are algorithms for things such as contrast enhancement, which
would be exactly what you don't want for your application.
It is worth looking for a camera vendor that will actually tell you
what processing is applied to the image, and perhaps even tell you how
to turn it off.
True.
Also, Spiricon, a company in Utah, makes commercial CCD-based beam
quality meters, and I think may have on their web site some notes by the
company founder, Carlos Roundy, on tricks of the trade in removing
background noise and tilt from the response of the CCD. I'm sure he
published these somewhere.
In fact, here's a small set of journal articles on the subject (mostly
not using camera CCDs, however):
[1] R. H. Burns, "A high-frame-rate CCD-based diagnostic for laser beam
quality.," in Phase Conjugation and Beam Combining and Diagnostics:
Proc. SPIE 739, pp. 181-8. 1987.
[2] M. D. Duncan and R. Mahon, "Beam quality measurements using
digitized laser beam images.," Appl. Opt., vol. 28, pp. 4569--4575, 1
November 1991.
[3] R. G. Waarts, "Optical characterization of grating surface emitting
semiconductor lasers," Appl. Opt., vol. 29, pp. 2718--2721, 20 June
1990.
[4] A. Cutolo, F. Ferreri, T. Isernia, R. Pierri, and L. Zeni,
"Measurements of the waist and the power distribution across the
transverse modes of a laser beam," Opt. Quantum Electron., vol. 24, pp.
S963--S971, September 1992.
[5] M. D. Duncan and J. A. Ruff, "An M$^2$ beam quality meter for pulsed
lasers," presented at Optical Society of America Annual Meeting,
Albuquerque, New Mexico, September 1992.
[6] J. A. Ruff and A. E. Siegman, "Single pulse laser beam quality
measurements using a CCD camera system," Appl. Opt., vol. 31, pp.
4907--4909, 20 August 1992.
[7] C. B. Roundy, G. E. Slobodzian, K. Jensen, and D. Ririe,
"Compensating for performance deficiencies of CCD and vidicon cameras
for laser beam diagnostics applications," in Laser Beam
Characterization, P. M. Mejias, H. Weber, R. Martinez-Herrero, and A.
Gonzalez-Urena, Eds. Madrid: SEDO (Optical Society of Spain), 1993, pp.
381--403.
[8] B. Eppich, R. Kostka, N. Reng, and H. Weber, "High power laser beam
characterization.," in Proc. SPIE 2206, pp. 469--482 1994. |
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| Louis Boyd |
| Posted: Wed Nov 05, 2003 8:22 pm |
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Guest
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AES/newspost wrote:
Quote: In article <6213f73a.0311051048.662d612a@posting.google.com>,
Detector195@yahoo.com (Detector195) wrote:
bassw@hotmail.com (Bas) wrote in message
news:<8fe46d4f.0311050706.71919032@posting.google.com>...
Hello group,
i want to measure laser beam diameters and plan on doing so with a
cheap USB webcam (lens removed of course and with a strong ND filter).
Does anybody have experience with this?
I tried with a CCD camera, but i fear that with the conversion to
TV-signal and the subsequent frame grabbing you mess up the resolution
along the line of pixels. Am i right that with a webcam the pixels on
the (CMOS?) chip correspond one to one to the pixels on the screen?
And do these camera's corrupt the image with compression? Any advice
on models to buy or to avoid is welcome.
Thanks in advance,
Bas
I don't know about actual brands, but I do know some things to watch
out for. Many CCD cameras feed the image through some digital signal
processing. This is even true of cameras that produce analog output.
There are algorithms for things such as contrast enhancement, which
would be exactly what you don't want for your application.
It is worth looking for a camera vendor that will actually tell you
what processing is applied to the image, and perhaps even tell you how
to turn it off.
True.
Also, Spiricon, a company in Utah, makes commercial CCD-based beam
quality meters, and I think may have on their web site some notes by the
company founder, Carlos Roundy, on tricks of the trade in removing
background noise and tilt from the response of the CCD. I'm sure he
published these somewhere.
If cheap is the requirement however you might consider using an older
surplus B&W ccd industrial camera along with a video card which uses one
of the Brooktree chips (BT848 or similar). That would run about $25 for
the framegrabber and maybe $50 for a used camera with gamma setable to 1
(linear). If you run Linux there are drivers such as BTTV with source
code allowing you to be sure you have control over the image
processsing. With either an analog or USB camera you'll be limited to
8 (or less) bits of dynamic range.
USB cameras have a couple of limitations. One is their small physical
size and the other is only being available in color versions (at least I
haven't found a B&W one) which cuts into their resolution. If you're
working with IR lasers those filters cause trouble. I've used
industrial B&W cameras to observe yag lasers at 1064nm though not as
direct beam profilers.
--
Lou Boyd
http://www.fairobs.org |
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