harbor freight micrometer

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Joe Farina

harbor freight micrometer

Post by Joe Farina »

I was wondering if anyone has tried the following micrometer for measuring DCG layer thickness:

http://www.harborfreight.com/digital-mi ... 98485.html

They say on the website it has a resolution of 0.0001 inch, but on the package it says 0.00005. (0.0001 inch would be 2.54 microns) The price is $34.99, but occasionally it goes on sale. Very high precision wouldn't be needed, but I would like to know if my coatings are around 15, 20, 25 microns, etc.
Dutchelm05

harbor freight micrometer

Post by Dutchelm05 »

I use this type at work and I bring in plates once in a while to measure.
One thing to keep in mind Joe, there are types in which when you rotate the micrometer the tip also rotates. This is not the best thing rather the prefered type is the tip that simply goes up and down.
Good price though,
Good Luck

Tony
Joe Farina

harbor freight micrometer

Post by Joe Farina »

Thanks Tony. It will still probably be a destructive method, though; measure the glass/gelatin, scrape off the gelatin, measure at that same spot again, and subtract for the glass.
Colin Kaminski

harbor freight micrometer

Post by Colin Kaminski »

I thought we sorted out an optical method to measure this? Am I mistaken?
Dutchelm05

harbor freight micrometer

Post by Dutchelm05 »

Using a spectroscope requires that you coat a mirror I believe.
Am I mistaken? :?
Thieu

harbor freight micrometer

Post by Thieu »

Strictly you don't need to coat a mirror, you'll get interference from the reflections at the air->gelatin and gelatin->glass interfaces. The interference will cause dips in the reflection spectrum at (approximately) equally spaced wavelengths. From how many dips you see per wavelength interval you can calculate the thickness. At my previous job I wrote software to fit a theoretical spectrum to a measured one to measure antireflection coating thicknesses this way. It also worked well for the emulsions. Because the difference in refractive index between glass and gelatin is very small, the reflection at the second interface will vary from almost nothing to a couple of tenths of a %. So the dips are shallow. I don't know if you'll be able to see them by eye. For a free standing layer they'll be very easy to see.
Dutchelm05

harbor freight micrometer

Post by Dutchelm05 »

I guess I recalled this post.
http://holographyforum.org/phpBB2/viewt ... ess#p41567
Have you tryed it with glass Thieu?
Colin Kaminski

harbor freight micrometer

Post by Colin Kaminski »

I was thinking of something like this:

http://www.sciencedirect.com/science?_o ... archtype=a
Thieu

harbor freight micrometer

Post by Thieu »

This morning I tried both techniques. For the first type I looked at the reflection of the sun on a small portion of the plate through a grating. I could not discern the dips in the spectrum. For the other type I reflected the unfocused beam of the blue diode onto a screen. It also generates a reflection with a slow variation of the entrance/exit angles. No luck there either. I guess the contrast is just too low. I used photoframe glass with a couple of um's of knox (finally made some plates Joe :-) ) I'm afraid the conclusion has to be that the shallow dips can only be seen with a digital spectrometer like the one I used at work. It worked well there with the same gelatin on glass coatings.

Btw, if you use mold coating, you can use rainex on parts of the plate that are normally coated. Then the layer can easily be pealed off. This certainly works with the spectral technique, I use it as a demo for students in a wave optics class with mica plates. The dips show up really well in that case.
Colin Kaminski

harbor freight micrometer

Post by Colin Kaminski »

Thieu wrote:This certainly works with the spectral technique, I use it as a demo for students in a wave optics class with mica plates. The dips show up really well in that case.
What mica do you use? I need some optical grade mica about 50mm in diameter and a mm or so thick.
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