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Sun January 19, 2003 (4am)

I've managed to place my second diode in the housing and collimate the beam.

Unfortunately the camera focused on the newspaper rather than the housing but you can still get a bit of a sense of scale.  I had to apply a huge amount of force to get the diode fully seated.  It "popped" (alarmingly so) into place and there's no way it's coming out of the housing.

Here's a shot of the whole thing again just prior to putting the circuit case back together.  The well collimated laser is shining on the pliers in the upper right.

Monday, January 20, 2003

The following is a message and video I posted to the Holography Forum.  I got tons of useful replies.

Has anyone gone to the trouble of writing up how to diagnose what fringe behavior means? I've been documenting my re-entry into holography as well as making sure to test for problems I ignored on the first go-round. Once I'm shooting again, I'll be putting video up on what problems I had, how they can be recognized and what to do about them.

I'm having a problem with my new table and I don't know if what I'm seeing is caused by temperature shifts cooling the laser diode, mode hopping, thermal instability of my table top (1/4" steel) or radio interference.

I'll be posting a video of the fringes later tonight, but in the meantime...

What I'm seeing are rock-solid fringes with an occasional blurring.

Once the table has settled (after just a few minutes) I can mark a dot on the wall and the fringes don't move relative to the dot. What they do though is behave as though I'm modulating the laser (at least, that's how I interpret the blurring). It makes me think that there's a single frequency signal being applied for a short period and then turned off.

It's not regular, but when it happens I'll frequently see a steading blurring once every 8 seconds +/- 3 seconds.

I do see similar blurring (although much more active and variable) if I blow lightly toward my table (from 5-6 feet away).

The video is here (1.5MB)

Wednesday, January 22, 2003

Well, I couldn't try batteries as I didn't have the hardware to hook up eight AA's. I do now, but it will have to wait until I get home from work.

I was able to try another wall transformer that claimed to put out 9v and actually put out 15. When I hooked that to my driver I got nothing but blur. To my untrained mind, that implies that I may indeed have a voltage problem.

I noticed on hooking up the original 12v supply that the 7805 regulator got very very warm (almost hot) extremely fast. This doesn't seem like a "good thing" either.

I've just purchased a new aluminum project box and I'll be using it initially to help shield the ld from air currents and improve the heat sinking on the voltage regulator.

Thursday, January 23, 2003

Well, I hooked up two "batteries" last night. One 9v and one 10.5v made up of 8 1.2v AA's. I know the second should have been closer to 11.5 but 10.5 is what my meter recorded.

I definitely see a difference in the blurring behavior when running from these batteries. On average, the blurring is much less frequent once the system settles (thermally and physically).

Initially there was no blurring at 10.5v and then I did see some very minor blurring much less frequently than shown in the video I posted. I switched to the 9v battery and got nothing but blur for the first 10 seconds at least. Then it sort of settled into a semi-blur state for a while. I don't know how long that might have lasted as sleep was calling and I didn't want to leave it running overnight.

I'll have more time tonight to do some more scientific tests and get some video out.

I also have a variable voltage, regulated power supply on the way and I'll do some tests on that when it arrives (maybe tomorrow).

Friday, January 24, 2003

I ended up not having much time last night beyond testing a new power supply.

I discovered an even better parts store yesterday and purchased an inexpensive regulated 12v ps as well as a couple of heat sinks. One for the 7805 and a larger one that I'll be cutting up to create a diode head with a hole drilled where I'll put the thermister on a permanent basis.

The new ps puts out a reliable 12.25v up to a 3amp load. The old ps was quite variable.

At any rate, it appears that the majority of the blurring is (was, I hope) caused by unregulated input power. I wasn't seeing any blurring once the diode warmed up and only a little at the beginning.

I think that the remaining behavior could be attributed to thermal changes in the diode and mounts as well as the occasional air draft. If I leave the room for several minutes and come back in quietly, I have yet to see any blurring. The test works even better if I project the fringes to the office door across the hallway and don't even go back into my office. Because of the way my office is situated, there's very little airflow in/out of the office if my ceiling fan isn't running and the AC vent is closed.

I expect to receive a variable voltage supply today and I'll test the laser again at lower voltages this weekend.

It appears that one key is to this whole mess is to supply reliable power. I'm sure the EE's and more experienced people are saying "duh" at this moment. It's interesting what the mind will forget after an electronics lull of 15yrs. Especially when you're in a hurry to get "the thing" put together.

In any case, I'm going to try to make this weekend the weekend I:

o Cut some small film strips for testing.
o Put the processing chemicals into bottles, ready for mixing.
o Test my safelight, using film.
o Run a small holo test and develop.

/me goes back to crossing the i's and dotting the t's. no, wait. Dotting the i's and crossing the t's. Yes, that's why I have checklists...

Close up shot of the laser diode "mounted" with two washer sized magnets. I've got the meter attached to a thermistor monitoring the temperature of the diode.  The metal object at the bottom is the beginning of a heat sink head for the diode.

Here's a shot of the interferometer setup I was testing with this morning.

And I got silly and put the camera in the path of the spread beam.  The interferometer was set up so that the fringes were projected across my office to the far wall.

Video, 5MB
These are about 1' in diameter and barely moving.  If you click on the image, you'll be able to download a video of the fringes.  They're moving slightly due to settling of the table and air currents.

Overview of the table.  The table itself weighs about 400lbs.  I'll be moving the smaller cinder blocks so that they're on top of the inner tubes so that the table top is a bit heavier.  The top layer is 1/4" steel plate that weighs about 83lbs.

Unfortunately I don't have any shots of the top being prepared.  I cleaned it on both sides with paint thinner to get the oil off that had been used to keep it from rusting and then painted the entire top with a flat black enamel.

Saturday, January 25, 2003

I didn't have a lot of time to work on the lab due to other commitments (Irish Dance) but I did manage to finish my plate holder and paint all my epoxied mounts.  Late in the evening I mixed up the chemicals included with the JD3 kit from Integraf.

The plate holder prior to painting.  It's attached to the metal bar with three very strong magnets and has two nylon screws to hold the plate in place. The metal bar has four magnets on the base to hold it to the table top.

(later) Unfortunately this design isn't stable enough.  The mount rotates too easily and the nylon screws, while gentle on glass, shift too easily.  For the moment (as of Feb 2003) I'm using it directly on the table in a fairly simple setup and just allowing the plate to rest in the holder.  On the other hand, the other mounts are working great.

Everything being painted flat black.  Prior to painting I cleaned all the parts with paint thinner to get all the grease off.  The paint is high strength Krylon and holds on like it was part of the mount.

Some additional mounts being epoxied. I use flanges from the hardware store and metal bars glued together using epoxy.  Once that's cured I can screw the two parts together to form a very solid base.  I then attach magnets to the bottom (you can see a stack of bases in the upper-left corner of the picture) so that the base is held firmly to the table.  I generally have to use two hands to rotate and slide the mounts around which also gives me a great deal of control when I need to make fine adjustments.

Setting up for the first test shot.


Rebuilding | Week 1 | Week 2/3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 10 | Misc Thoughts


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