Joe Farina wrote:Hello Milan,
Hello Joe.
Awesome video, thanks.
Your DCG lab is quite complete and impressive, except for two (or maybe three) things: a good laser (and also preferably a reliable power meter to keep track of its output) and a good laminar flow area.
Whole day and whole night spent making 3 V stable PSU, power meter, power indicator (not real power, just to see whether power increase or decrease), finding the best operating point of the laser module (this took me many hours, too much), and other things.
Laser now running on 3V, 470 mA, giving stable 42 mW (okay, reading tolerance maybe '/- 5%, not sure my power meter is properly calibrated). But it working stable without mode hopping. Found that at 440 mA or less, it begins hopping frequently, as well as at or above 480 mA. So, I found 470 mA is the best. Tomorrow will setup improvised interferometer to see true stability.
Seems that all my problems with laser's instability is due to one small transistor close to 808 nm laser diode:
- When this transistor overheats, beam brightness begins to cease and make mode hopping.
I remove this transistor, solder three wires, and put two transistors (darlington pair) outside module. Laser works much more stable now.
Also, make one toy: 'polariscope'.:
- It is essentially two Brewster's plate, each for separate polarization, angled 90 degrees each to other. Working well.
- This 'toy' showing that this laserpointer has very bad polarization ratio. If polarization is okay, just one of two side beams should be visible.
Tried to remove rest on unwanted polarization with BGO crystal (haven't any suitable polarizer, except for photography - too much attenuation):
- Lost about 50% of incoming beam, but it is much better than 'raw' beam. Ratio of polarization is much better. Note small spot on top of polariscope - almost invisible.
- At Brewster angle, small amount of wrong polarization remains. Even this small amount can make troubles. Note how much on top of polariscope remains. I want to remove this, but haven't proper polarizing beamsplitter. Tried BGO crystal (it has high refractive index, and reflecting cca. 40% 'good' polarization). How it works is shown on previous picture (above).
What I found with my 'polariscope' is that all my holograms are made with misaligned polarization by 30 degrees (too much, trusting polarizing sunglasses - too bad idea). So, part of my problem with unwanted interference fringes at plates are due to this issue. Now, some fringes remains, but much less visible.
I am wondering if those medical masks are true hepa-type filters? If they are, then they should be ok. Also, I'm wondering why you're using 7 layers of pre-filter material. Shouldn't one be enough? I don't use any pre-filters, just the hepa. Your flame isn't bending -- it needs to bend. It should be easy to find a cheap fan that is strong enough, if your current one isn't.
Not sure either, only know that there are three layers, and middle one is electret (electro-statically charged), and that this layer actually doing it's job. Only thing what I don't know is how it is effective.
7 layers of pre-filter is because without that it causes turbulent flow (I had no clue how this device actually looks like). About fan: I will try to do something about that.
Of course, you can use any kind of honeycomb structure other than straws. John Pecora uses a grille that we often see under fluorescent light fixtures that is white plastic in the shape squares. I'm not sure if he uses just one, or multiple sheets glued together to form a longer honeycomb, more than one seems better to me. But this item may not be easy to find. You will have to use your own ingenuity here (which I see is considerable -- homemade doubling crystals, wow). The grille must be clean, and not friable (i.e., it must not generate dust). If the material is friable, it can probably be made non-friable by coating with varnish or shellac.
Yes, I will try to find something which may serve for that purpose. Ah, homemade doubling crystals... not the perfect ones, but can double.:
http://www.milankarakas.org/pub/KDP/HomegrownKDP.html
You mentioned that the top cover was removed. It does need a top cover, and also covers for both sides (you're using the tabletop for the bottom cover which is fine). The area in front of the hepa/grille needs to be box-like, this is the clean area where the coatings will be made. Also, importantly, the front opening of the box always needs to be covered when not in use, to prevent dust from getting inside and corrupting your grille. I use a piece of rigid plastic film with magnetic adhesive tape around the edges. The front of my box also had magnetic adhesive tape, so that it "mates" with the magnetic tape on the plastic film.
I put top cover because it improves slightly cleaning ability (too weak flow). And, I will make some cover after using laminar flow hood. Magnetic stuff is good idea. Thanks for this advice.
By the way, I saw your solution of Rhodamine 6G. R6G can increase the sensitivity of "classic" DCG to green light. If you don't already have that paper, please PM me your email address, and I will scan and send it to you.
No, I haven't that paper, will send you PM. Tried once by guessing amount, but not working well. Maybe there should be some other additives?
Best--
m--