Achieving a smaller beam diameter with 803T optics

Re: Achieving a smaller beam diameter with 803T op

I'm using this one:



the one with the 4 little white plastic things around it, and it's very tiny? well, smaller than the arcylic one atleast. You can see in my post above that the lens I used has the same circular pattern as the one in the original post, but notfocused dot. I should only have 1 lens inside the knob right?

Re: Achieving a smaller beam diameter with 803T op

looks like all those pic's are fake but the secound one!

Re: Achieving a smaller beam diameter with 803T op

i think you have a too large distance between the lens and the diode. when screwing the lens (only the new one, alone! old one out!) in, does the "dot" get smaller, until you cant go any further? do you use a regular aixiz module? look into it: does it have the threads all the way into the module, down to the diode itself? there are the real ones from aixiz, and bad ones from dx, with threads stopping halfway, so you cant get the lens close enough.

..more to come when you give hints

manuel

Re: Achieving a smaller beam diameter with 803T op

Hi, sorry for not replying for a while.
In this mod we put the lens in the piece of plastic behind the lens nut. The one that holds the stock lens in place. We need to sand the lens down a tiny amount so the new lens will fit inside of the lens holder. Mikeeey, I'm pretty sure you got it, just keep screwing the lens down until you get a dot. Remember this lens has a small focal point, so we want to get the lens as close as possible to the laser diode.

Re: Achieving a smaller beam diameter with 803T op

Jimmymcjimthejim said:

In this mod we put the lens in the piece of plastic behind the lens nut. The one that holds the stock lens in place. We need to sand the lens down a tiny amount so the new lens will fit inside of the lens holder.

Click to expand...

hmm, i didnt really get how you mean it, probably just like i did it too?
step-by-step, just to be sure, how i do it:

i screw the black lens nut into the metal housing, just how it belongs. then i push onto the acrylic lens, with guessed 10 pound pressure, until it suddenly gets lose. if you use something made of plastic and perhaps tissue-paper in between, it wont even be scratched. i use a plastic pen.
you now have: a hollow black plastic nut with threads, a lose acrylic lens and a black "washer" which held the lens in place.
glue your new (dvd/br-pickup-) lens onto the "washer". for that, you have to widen the hole a bit. you will figure it out!
the lens is on the flat side of the washer, the round side of the lens at the washer.

# #
# #
# #
# ++ #
# +++++ #
#######++++++++#######
+++++++++++
++++++++++++
++++++++++

all right, thats my first attempt of ascii-"art", could have made a photo in that time!
# is the "washer"
+ is the new lens

dont use regular acrylic-glue, it fumes and screws the lens up!
try to glue the lens centered and even.

now push the washer back into the hollow nut, just like it was. you now have a nut with only one lens, the new one, which sticks at the bottom of the nut. with regular aixiz holders (which are threaded all the way down), you are now able to screw the net/lens down right until it touches the diode. no, thats no good idea actually! oh, i had to shorten the original spring to half of its length too.

when you screw the lens in, you first have a large blob, as in the pics, then it gets smaller, is a dot, and spreads out again for the last few turns until the lens touches the diode.


i couldnt describe that with more words than now. once you did it, its more than clear and obvious. and yes, you get a nice round dot, with small beam-diameter, and with little specle around the dot! definitely worth experimentation, thats why i annoy you people with painfully detailed instructions!

manuel

Re: Achieving a smaller beam diameter with 803T op

Thank you Krutz. You pretty much covered it!

Re: Achieving a smaller beam diameter with 803T op

Well all I managed to do was get the glass on the diode dirty from the lens making contact with it... and even then, it wasn't focused enough.. lol. I think I'll just wait on IgorT's glass lens's.

Re: Achieving a smaller beam diameter with 803T op

mikeeey said:

Well all I managed to do was get the glass on the diode dirty from the lens making contact with it... and even then, it wasn't focused enough.. lol. I think I'll just wait on IgorT's glass lens's.

Click to expand...

Then you screwed it in too far!

Great job!!!

Thanks for reviving that thread and reminding me, I wanted to try this out as well!

As for the lens orientation: the final lens (which we're discussing here) takes a parallel beam and focuses it into a pinpoint a few mm's away. So I'd think the side that faces out from the sled (the one toward the DVD) should be the side facing the diode in this mod - we're running the light through it "backwards", creating a parallel beam out of a pinpoint emitter.

Also the lens next to the LD in the sled should have similar (or maybe even better) properties...

Uhm ..... never thought that, those rings, can be due to a diffraction fresnel-type grating, printed directly on the lens ?

I tried those lenses times ago with red, green and blu-ray diodes, and got all the same results, a circular diffracton serie of rings, looking as a fresnel lens, also if all the lenses that i've tried was looking perfectly transparents, at sight.

Anyway, i don't have a microscope, so can't check ..... can be interesting if someone with a 100x, or so microscope, want to examine both the sides of one of those lenses, for see if my idea is wrong or not .....


The only other idea i had, is that the lens is so strange shaped, that can cause optical interferences inside itself

I've done some experimentation yesterday, nothing final due to a near-complete lack of proper tools. I got the lens out no problem; it is indeed mounted with the flat side toward the focus point. Mounting it with the rounded side toward the diode will lead to an increased angle of incidence of the rays onto the lens and thus greater reflection losses.

I even managed to disassemble the Aixiz lens housing. That Aixiz lens is fat, no wonder it has about 30% loss. However, I could not yet mount the new lens permanently, I just sort of balanced it inside the housing. The housing has to be screwed in completely - and then some more, to achieve focus (while it was not yet focused, it looked like mikeeeys picture). Due to the aforementioned handicap I could not do a proper focus test; however the beam looked quite spectacular - needle thin instead of the Aixiz thick wooliness.

If you look at the lens at the proper angle, you can see a series of concentric rings (I used a 10x magnifying glass, no need for a microscope). I guess that's from the manufacturing process, as the lens will be aspherical. I don't think it's part of the working design.

With the Aixiz lens, I can get a very nice tiny dot after 5m. I wonder how the new lens will perform once I get it right.

One BIG request:

Can someone with a LPM get a comparative power reading of the new lens vs. the Aixiz (xx% gain)?

i compared several lenses with readings a while back..
http://laserpointerforums.com/f49/results-different-lenses-red-br-efficiency-34041.html
no pics and only one br-lens though.

if there is enough interest, i will redo a test with all different lenses i have available (10?), with readings and photos. wont be soon though, i am really busy these weeks.. but i have this thread subscribed ;-)

manuel

Read your article... the "s are rather distracting :undecided:

If I interpret your numbers correctly, they greatly disagree with what LarryDFW, Milos, Jayrob et al. reported in the 405-G-1 lens threads. According to you, for BR:

no lens: 13mW
Aixiz acrylic: 11mW

so there should be less than 20% gain possible. However the BR-coated glass lens gives +30% according to all other measurements, and it still absorbs or scatters 5-10%. So with BR, a standard Aixiz acrylic lens should give only about 75% of the no-lens power...

Maybe you can repeat the readings with a "standard-power" 803T BR laser (i.e. around 100mW), taking care that the dot covers a significant portion of the sensor. Both should greatly increase the precision.

For this thread here, only the comparison between standard Aixiz acrylic and the 803T sled lens is "in scope", no need for a mass comparison :thanks:

EDIT: I checked Jimmymcjimthejims first post in this thread, there's a picture of the dot. It looks like the beam is off-center to the lens. In mikeeeys picture, it's just a tiny bit off. I think getting the lens centered correctly and perpendicular to the beam is crucial for a good spot. That promises to be quite a challenge.

three problems with my readings:
1) its low-powered, at the edge of what a thermal lpm reads reproduceable
2) spot-size: the smaller the dot, the higher the reading, to a point..
3) its a kes300a diode. perhaps its wavelength is higher than usual, which would reduce the aixiz' absorption.

yes, you already found those flaws ;-)
will make comparisons soon!

thats the tricky part about all 405nm optimized lenses. they are "good". you can only compare them to how bad the other lens is. if someone uses a 650nm coated lens for a bluray, he may gain more than 50% by switching the lenses ;-)

manuel

I've now used the brass housing of my Aixiz glass lens (which I took apart a long time ago) as a lens holder - the lens fit quite well over the diode side aperture, so I just glued it on with household glue (the brass should serve as a good heatsink).

First, as mentioned, the scatter increases a lot (which doesn't bother me too much). Over 5m, I could get a nice small spot, about as big as with the Aixiz (I didn't take measurements or pics, just visual impressions), but more light around it. Part of that may be because the lens looks a bit scratched, possibly the AR coating is damaged. I don't know whether that's from my handling or whether it was already a bit worn from whatever was done to it before. In any case, assume it's sensitive!

Next, I shone the laser at the wall of a house about 50m distant, observing the spot through 8x30 binoculars. Here it's quite obvious that the divergence from the Aixiz is a lot better - at least twice as good I'd say. Over this distance, the Aixiz just showed a bright spot with very little scatter, while the 803T lens had some rings and also two "wings" (a bit like the famous line of the red LOC, but diffuse). Maybe I can get some figures and pictures later (in the next days).

So, which is better - standard Aixiz or this mod? I'm not sure yet... I think this also depends on the actual power performance of the 803T lens. If it gives a big gain, it'd be a definitive plus...