Message Board Thread - "10 µm by 10 µm spot - can it be measured or seen?"

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10 µm by 10 µm spot - can it be measured or seen? Andrew Szelc 6/8/2006

Our company is considering a purchase of a high standard, fast frame rate (>200 Hz) imaging radiometer with a high quality close-up/microscopic objective lens. Our intention is to use such a set to observe and measure a thermal signature of a tiny temperature point made by a high power laser.

Please see the enclosed picture.

The red rectangular shape is the "hot point" - an area heated by the laser beam. The denisty of the input power (the impinging laser power) is between 1.04 and 3.12 Giga Watts per m^2. The laser wavelength is 830 nm. According to our FET simulation the temperature of the point reaches @ 1000 deg C. The surface emissivity is high (> 0.9) and the working distance between objective lens and the sufrace should be around 30 mm or less.

Since we will be measuring quite a hot target (>900 deg C), we intend to use a 3-5 µm or even NIR imaging radiometer. As for as we know, when dealing with high temperatures, short wave cameras are less susceptible to errors caused by wrong emissivity setting and also the NETD value is slightly lower for SW-TIs working in the higher temperature region.

We have already had one demo of a thermal imaging system from one of the european manufacturers. They brought a thermal imaging radiometer equipped with a standard close-up lens and we were trying to seize the spot. Unfortunately, despite our efforts, we were not able to find it (probably due to the fact that its dimensions were far below spacial resolution of the demonstrated system).

Our questions are as follows:

1. Will it be possible to see our 10 by 10 µm^2 "hot point" with a thermal imaging system that works in the region of short or mid-infrared (1 µm - 5 µm)? The target's dimensions are comparable to the wavelength we will be using...
2. maybe in order to rise spacial resolution we should go down with the wavelength and simultaneously increase the diameter of the objective lens. But will it be enough? There are some commercially available, high frame rate thermal imaging systems (usually, InGaAS and InSb arrays based) that utilize short- and mid-infrared region. Some of them can be armed with 10 µm close-up lenses (Phoenix and Merlin from FLIR are good examples). Having such a camera, would it be possible to measure, or at least to see, the "hot point"?
3. One of our R&D colleagues suggested that in order to achieve higher resolution per pixel we should use an array with a smaller pixel size. Well, we do not really know whether that is the right way and there are theral devices with pixels smaller than 30 µm by 30 µm. We could accept a smaller pixel and even at the expense of reducing the sensitivity.
4. The laser is aimed at the surface at a certain angle in order to decrease the influence of a reflected apparent temperature. Is there any spectral filter that could be installed on the camera to cut-off the laser beam radiation (830 nm)?
5. In your opinion, would it be possible to use NIR imaging radiometer combined with a standard, fine quality microscopic lens made of standard optical glass? Mr Austin Richards from IndygoSystems used a standard photographic objective lens in his Vis-NIR (InGaAS based) camera.

And that is all for now...

We will appreciate any info. Thank you in advance for all your comments.

Best regards,
Andrew Szelc, ITC-Level II, AGFA Gevaert N.V., Belgium
Re:10 µm by 10 µm spot - can it be measured or seen? Hay 9/30/2006
Beste Andrew,

I am wondering if you solved your problem, if not maybe I'm able to help you.


Hai Theunissen
EN 473 niveau 3 thermograaf
THEOLT thermografie & techniek
Spoorstraat 155
Tel. ++31 485 54 1293
Fax.++31 485 54 1575


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