why there are some Black stripes on the hologram

[nobo]

I am really interested in hologram and I did some experiences in laboratory. However, I don't know why there are some Black stripes which seems somewhat regular on my hologram.
I tried many times but the black stripes still exist and i really hope anyone could help me figure it out. Thank you very much!!

[Joe Farina]

Black stripes in a hologram are often caused by a mode-hopping laser diode. These are also called "contour fringes" and cover the image of the object in regularly-spaced bright and dark contour stripes, making the object look like a zebra.

[nobo]

Black stripes in a hologram are often caused by a mode-hopping laser diode. These are also called "contour fringes" and cover the image of the object in regularly-spaced bright and dark contour stripes, making the object look like a zebra.

Thanks for your answering!

I know little about the laser and have not heard about the mode-hopping.So does it means that I may need change my laser in order to make a perfect hologram?

And as you know, there are many different kinds of hologram and When I using the following method showed in the picture, the hologram would be okay.

[nobo]

Black stripes in a hologram are often caused by a mode-hopping laser diode. These are also called "contour fringes" and cover the image of the object in regularly-spaced bright and dark contour stripes, making the object look like a zebra.

Besides the parameter of the laser is MRL-III-671nm-50mW and when I adopt the following scheme showed in the picture, the hologram looks like a zebra.

[Joe Farina]

Most laser diodes are prone to mode-hopping (or slight changes in wavelength) during a holographic exposure, but the effect is unpredictable. I always recommend helium-neon lasers for this reason. They are available at reasonable cost, on eBay for example.

The way to be certain that those stripes are due to mode-hopping is to observe them closely: if they seem to cover the object itself (like they are tattooed on the object) then it's mode-hopping. If the stripes seem to be located on the film plane, then it's something else.

[nobo]

Most laser diodes are prone to mode-hopping (or slight changes in wavelength) during a holographic exposure, but the effect is unpredictable. I always recommend helium-neon lasers for this reason. They are available at reasonable cost, on eBay for example.

The way to be certain that those stripes are due to mode-hopping is to observe them closely: if they seem to cover the object itself (like they are tattooed on the object) then it's mode-hopping. If the stripes seem to be located on the film plane, then it's something else.

fantastic！ I will try to change my laser and find out the problem. Thank you so much!

[Joe Farina]

This is one of my favorite discussions on laser diode mode-hopping:

http://assets.newport.com/webDocuments- ... ode_IX.PDF

Below, I've attached a few pages from a long paper which illustrates the "zebra" effect on holograms of objects, when "two" closely-spaced wavelengths of light were used (they were using a dye laser in this case). The same effect happens when a laser diode mode-hops.

contourfringes563.pdf

(652.46 KiB) Downloaded 257 times

Also, below is an example of a helium-neon laser which can be found on eBay:

http://www.ebay.com/itm/Helium-Neon-Las ... SwuTxV9OFR