I would have to vote for mode hopping as someone who has seen his share of it.
But hey the easiest way to end it is very ridge object like ball bearings. Make a fairly large spaced triangle place the plate on top, place cardboard panels all around the object that won't imped the beam, allow as long a settle time as you can stand (like 15-20 minutes) and that should tell you. Do a single beam set up in which the object is glue to the table.
A good science project is to try a Michelson interferometer set up and see what is going on. There is lots of info on the web on how to set one up.
The object should be 3D not a coin since if it was mode hopping, a flat coin may not show the problem. If it is mode hoping, stick with flat objects until you figure out what is going on with the rest of your process. If you still like holography, then spend a few bucks on a better laser.
Good Luck,
Tony
Horizontal stripes on red hologram
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Joe Farina
Horizontal stripes on red hologram
Dutchelm05 wrote:I would have to vote for mode hopping as someone who has seen his share of it.
Yes, me too :wall: Object movement usually shows irregular, and typical localized dark areas or bands. Mode-hopping, on the other hand, makes your three-dimensional object look like a zebra. The bands go everywhere. But as Tony and Bob said, the object needs to be adequately deep for the mode-hopping bands to show up. If the the coherence length is longer than the depth of the object, the object may appear normal, or it may be dim or even vanish, depending on how things are set up. Coherence does not go out abruptly, though it appears to do so when the coherence is short, like it is with some diode lasers (with longer coherence length, like with a HeNe, it would obviously fade in and out). I have a paper about intentional depth-contouring using this principle (the authors used a dye laser whose coherence could be easily changed by adjusting it). They had a photo of a coin (I'm pretty sure it was a dime), and they adjusted the laser to have a really short coherence length, maybe less than 1mm. Those contour bands were going all over the front surface of the coin.-
wler
Horizontal stripes on red hologram
As for coherence length: there are different situations with different symptoms, depending on the shape of the laser emission wavelength(s):
1) The situation is simplest if there is a single narrow line; then the coherence length is determined by the line width, and if the latter is small, then the coherence length is large (typically tens to hundreds of meters).
2) Conversely, if the line width is large but still looks like a continuous gaussian peak, the coherence length is reduced, and leads to fading out in the hologram (ie, reduced depth).
3) If the emission consists of a few distinguished narrow peaks, then there is a periodic fading in and out, and this leads to banding. This "multimode" emission is typical for argon, DPSS and other lasers (unless special effort is made to suppress it).
4) If the emission consists of many narrow peaks, then the situation is in-between the above two, and if the number of peaks becomes very large so that a continuum is approached, then situation 3) approaches 2), ie, the banding becomes finer and finer and one approaches the "fade-out" scenario. This is typical for high-power laser diodes.
1) The situation is simplest if there is a single narrow line; then the coherence length is determined by the line width, and if the latter is small, then the coherence length is large (typically tens to hundreds of meters).
2) Conversely, if the line width is large but still looks like a continuous gaussian peak, the coherence length is reduced, and leads to fading out in the hologram (ie, reduced depth).
3) If the emission consists of a few distinguished narrow peaks, then there is a periodic fading in and out, and this leads to banding. This "multimode" emission is typical for argon, DPSS and other lasers (unless special effort is made to suppress it).
4) If the emission consists of many narrow peaks, then the situation is in-between the above two, and if the number of peaks becomes very large so that a continuum is approached, then situation 3) approaches 2), ie, the banding becomes finer and finer and one approaches the "fade-out" scenario. This is typical for high-power laser diodes.
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Colin Kaminski
Horizontal stripes on red hologram
I have not had problems with Integraf's laser but I do make sure to warm it up for 30 minutes or so before use.
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jnhong
Horizontal stripes on red hologram
It doesn't take 30 minutes. Ten is plenty. I bet even five minutes is okay. I've used the Integraf diode a lot. I power it up when I start preparing for a shoot in my "dark room". It's just that I always take at least 10-15 minutes to get everything ready to expose a plate, so I've never tried just 5 minutes power up. On the other hand, my ThorLabs 635 nm LDM is stable within 5 minutes. I just watched it the other day using my DIY light meter.
This guy might be experiencing the back reflection problem I was having. Angle the plates so little direct reflections come back to the diode. Maybe that will help.
Joe
This guy might be experiencing the back reflection problem I was having. Angle the plates so little direct reflections come back to the diode. Maybe that will help.
Joe