Image Issues

bryuly · Post by **bryuly** » Tue May 25, 2010 7:23 pm

Hi,

I am doing some research with holograms. I have been getting good images with the transmission set up I have been using, but now I am wanting to take images of vibrating objects and when I do I get really fuzzy object on the top half but on the bottom where it is being held it seems to be alright. I have tried as much as possible to get all of the vibrations out of the room but the room does have a heating and air conditioning system that I can not control. I have covered the vents. Is there too much vibration from air still or maybe the vibration device itself? The vibration device however has been on before and I got reasonable images with it on. Maybe certain frequencies? Is there something wrong with how I am developing them? Develop doesn't seem likely since I have been using the same time for all of them. Maybe a couple bad plates?

Thanks for any help.

I am using VRP-M plates and JD-2 developer on a vibration dampening table .

jnhong · Post by **jnhong** » Wed May 26, 2010 1:38 pm

It seems you already understand that vibration and holography don't mix, but your goal is to create a hologram of a vibrating object. You need to explain this: what should the hologram of the vibrating object look like? Is it supposed to look like it was also vibrating when reconstructed? Did you want the hologram to appear as if the object were moving? How would that look like? Did you want to capture "motion blur" in the holographic image?

How should the hologram of the vibrating object look like compared to the same object when it is NOT vibrating? If the holograms have no differences, then just shoot the non-vibrating object and be done with it.

Once you have CLEARLY answered those questions, we can go into details of your laser pulse and exposure energies and bench stabilization. What? You're not pulsing your laser? Err........

Joseph

bryuly · Post by **bryuly** » Wed May 26, 2010 6:48 pm

Yes I get that vibrations are bad. I am attempting to take images of vibrating objects to see the modes of the material. For example the picture of the bell here has modes.

: image.JPG (13.97 KiB) Viewed 3093 times

I do not want any motion blur. As you can see they will be clearly different when vibrating and not...so I need the vibrator on.

Also here you can see different modes of a plate.

http://www.puertovaras.tv/video/NGeNvn8 ... plate.html

MfA · Post by **MfA** » Wed May 26, 2010 9:12 pm

No experience with it, but I can provide the name of the technique you are trying to describe ... Time Averaged Holographic Interferometry.

At a guess, there are no true nodes and everything is vibrating at some harmonic with displacements substantially larger than a wavelength? (Consequently not showing up on the hologram.) Can you reduce the amplitude of the vibrations during the time of exposure?

bryuly · Post by **bryuly** » Wed May 26, 2010 10:26 pm

I have looked up where the nodes should be and have tried a couple images now. I in fact got one to somewhat turn out to where I could see the nodes, but some parts of the plate (mainly top and some of the middle) is not very clear. So I am guessing I need a better way of holding the plate still...?

The amplitude is already at a minimum when taking the image. So, I may try a more powerful laser and reduce my image time as opposed to figure out how to reduce vibrations...since I have already tried to get them to as minimal as possible.

Do you know if it is possible to get the same effect/image with two shorter exposures and a higher powered laser?

dave battin · Post by **dave battin** » Wed May 26, 2010 11:59 pm

what are you using as your transducer?

jnhong · Post by **jnhong** » Thu May 27, 2010 2:49 am

Your plate's top and bottom must be flexing instead of just resonating. You will probably need to clamp them down some more. What frequency and duty cycle are you modulating your laser?

MfA · Post by **MfA** » Thu May 27, 2010 3:35 am

bryuly wrote:Do you know if it is possible to get the same effect/image with two shorter exposures and a higher powered laser?

Frozen Fringe Holographic Interferometry ... doesn't measure quite the same thing obviously, that measures displacement modulus the wavelength (you'll need a pulse laser).

Colin Kaminski · Post by **Colin Kaminski** » Thu May 27, 2010 4:34 am

Holographic Interferometery of vibrating objects is quite advanced. I have played with it a little. The best results I have gotten are to take a hologram of a still object then project it on to the model and vibrate the model. Not as bright as making Time Averaged Hologramic Interferograms but that process has eluded me. Also consider speckle interferometry. All three process can be found in Optical Holography by Hariharan. Better math for making measurements can be found in Holographic Interferometry by Vest.

Please post your results!

bryuly · Post by **bryuly** » Thu May 27, 2010 1:53 pm

For the transducer I assume you are referring to how I make the vibrations. I am using a Pasco Scientific mechanical wave driver.

: SF9324_330_32255.jpg (8.8 KiB) Viewed 3060 times

jnhong wrote:Your plate's top and bottom must be flexing instead of just resonating. You will probably need to clamp them down some more. What frequency and duty cycle are you modulating your laser?

That is what I am assuming I think I will try to get a better plate holder. Does anyone know of a good one that can hold all sides still? As for the frequency and duty cycle is there an easy way to tell?

Colin Kaminski wrote:Holographic Interferometery of vibrating objects is quite advanced.

Really? I have gotten some images already and I just started with holograms 3 weeks ago. I have been working at it a lot, granted, but I don't know that it is as hard as you make it sound. I got a partial image on one, however the plate is fuzzy in places like I said before. Hopefully I will get a good image once I get a better plate holder. I will Post results once I get it to work for sure!

Colin Kaminski wrote:Also consider speckle interferometry. All three process can be found in Optical Holography by Hariharan. Better math for making measurements can be found in Holographic Interferometry by Vest.

I will definitely look into that and will try to find those books somehow...Thanks for the help. I appreciate it!