Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



New! Sharp Diodes 1W 520nm & 5W 455nm & +2W 638nm

Alaskan

Well-known member
Joined
Jan 29, 2014
Messages
12,937
Points
113
Quote: Robert, Redcowboy:

That's good news about the backfill gas being added back !

I am thinking about how these FAC will act upon the beam, also he has a version with a bar shaped output but it could be the better far field performer, I will test the 4w 445 FAC when I get it and look for your results with the green, I have several 1w green builds but I have long wanted to correct that bar shaped spot, if these FAC diodes have a clean output and perform well then I will have to buy some and the blues will be better for knife edging now that they have this FAC, no need for incorporating the c-lens pair.........dam I still have PBS cubes and that host you sent me, these may be just what the Dr. ordered...........just use a coli lens and align to the cube, could even skip the rotator and just rotate one beam 90 to PBS combine 2 beams.

That thought occurred to me too, we can PBS cube combine two diodes which are FAC corrected like this without a plus, or + shape being made, no need for a rotator! Just a nice square :) which will appear as a normal round beam to the eye, unless spotted on a surface, that is.

Edit: The diodes I ordered are being sent to Robert/CDBEAM777, he will need to report on them as I won't have them until he is done with a build he is doing for me.
 
Last edited:



Alaskan

Well-known member
Joined
Jan 29, 2014
Messages
12,937
Points
113
Agreed, for a strait 4 x knife edge the uncorrected beam would be better, but for what we are working on, I think the square is a better product due to reduced divergence of the fast axis. Earlier, I wanted cylinder pairs to fix the divergence problem but they weren't viable for us with that project due to the size as well as cost, but with these that problem no longer exists. I don't like the lower power of the NUGM03 compared to the NDG7475, but the reduced divergence is preferred due to wanting the beam to be much tighter. The lower output power for me is all numbers anyway, visually I won't be able to see the beam is a bit weaker, but I will be able to clearly see the tighter beam in the distance with the FAC lens.
 
Last edited:

RedCowboy

Well-known member
Joined
Jul 10, 2015
Messages
10,973
Points
113
If you take a 7475 focused to infinity and ( wear your laser attenuation glasses ) point it at a wall right in front of you.
You will see the bar shape, now walk backwards and after 6-7 feet you will see it start to transition, by 12 feet it was reversed, what was long is now the short and what was the short is now the long.
The whole thing is larger as it's diverged on both axis, but the fast axis has diverged faster and the fast axis is what was the narrow part of the bar.
So the FAC corrected diode ( with a coli lens added ) that produces the line I understand and can see the shape of the FAC lens in my mind, it will keep the far field bar from being so terribly long, actually far field it should be a short bar which should be much improved.
But the square output of the other option FAC corrected diode I am curious about, I have one ordered but I wonder how the FAC is shaped, even placed further out it looks like the fast axis is 1st over expanded then reduced, also I wonder how well it will hold square over distance.
Looking at it I don't see enough distance under the window can for the square output option to work like the linear output option which would be the conventional convex cylindrical design FAC optic like in the image.

This image would produce the two items listed below but I can't imagine the square output offering looking like this, maybe its a compound optic ?

PLD-FAC-Optics.png




Something like this:

uyfuyi2.jpg
 
Last edited:

RedCowboy

Well-known member
Joined
Jul 10, 2015
Messages
10,973
Points
113
Linear is the standard output only with the fast axis divergence corrected to match the slow axis divergence ( rate of divergence ), so the beam propagates as a rectangle/line without getting proportionally longer and longer IINM

It just seems like there's not enough distance under the window can to square the beam with only 1 FAC lens in the standard tombstone shape, but hey, if it works it works, I also have one of the squared output blues coming so if it's good I may PBS a pair, should be much easier without the rotator and c-lens pair in the optical train.

If you think about our coli lens it sits close to the facet and shows us an image of the junction shape plus divergence over the FL which is 2 to 8mm and the p/n junction is a thin line shape, so how far before the fast matches the slow so that our beam is square without anything but our standard coli lens......about 7 feet is what I measured today, so if the FAC slows down the fast axis( reduces it's divergence ) then it would need to 1st expand it to square the beam to the width of the junction...........that's why I think it's a compound for the square beam FAC diode, the " linear " is how I expect the FAC to work, but we will test and see what we get and if it works great, if not the linear beam shape would be great for knife edging and the beam won't grow wider and wider now that it's been FAC corrected, at least not at the normal aggressive rate.

That said the squared beam may work well, I am interested to know what the FAC is shaped like and if it over expands then corrects the fast axis much like a c-lens pair........again I understand how it works, it's the p/n junction geometry and the short distance from facet to FAC that has me wondering how it's being squared with just one FAC lens if the back side is flat.....but it may not be flat which could explain it, but if it works then great and by works I mean the beam stays square over distance.
 
Last edited:

Alaskan

Well-known member
Joined
Jan 29, 2014
Messages
12,937
Points
113
Now I see your concern, much for me to research regarding how a simple single FAC lens can work as a replacement to a cylinder pair.
 

RedCowboy

Well-known member
Joined
Jul 10, 2015
Messages
10,973
Points
113
If the P/N junction was closer to square I could easily see how a flat back convex front flat side ( single axis ) lens could square the bean in such a short distance..........of course it is very tiny at the facet so maybe there is room, I know there's room to reduce the divergence of the fast axis yielding a line/bar shaped beam but to square it would mean placing the FAC further away so the faster diverging fast axis can catch up to the junctions length........and as tiny as it is to start there may be enough room, but I do see horizontal and vertical aberrations around the image of the squared beam which doesn't really mean anything, mostly I have not set one up myself and it seems like there's not enough space but either there is or the backside of the squaring FAC may be concave......just thinking outloud and wondering how much bigger the squared beam is after a standard coli lens such as G2 or G8 and wondering if the linear might actually be better, will have to wait and see but I hope its as awesome as it can be, 1w of green in a tight square beam would sure sparkle in the night air :D
 

Alaskan

Well-known member
Joined
Jan 29, 2014
Messages
12,937
Points
113
I think I understand how this can work, in a cylinder pair the second lens just collimates the expanded fast axis, with the expansion lens next to the emitter, the collimation lens acts as the second lens to collimate the FAC corrected output and since both axis then match, a spherical collimation lens can do so without abberation because neither are collimated yet, both sides fast and slow are then expanding together at close to the same rate.
 
Last edited:

steve001

Well-known member
Joined
Jun 3, 2007
Messages
2,517
Points
113

Alaskan

Well-known member
Joined
Jan 29, 2014
Messages
12,937
Points
113
Only thing I could think is she meant line, I normally think of a "spot" as something different from a line.
 

steve001

Well-known member
Joined
Jun 3, 2007
Messages
2,517
Points
113
Now I see your concern, much for me to research regarding how a simple single FAC lens can work as a replacement to a cylinder pair.
Cylindrical pairs are used to circularize a laser's beam. If the objective is to not do so than one lens can be use to beam shape.
 

steve001

Well-known member
Joined
Jun 3, 2007
Messages
2,517
Points
113
If the P/N junction was closer to square I could easily see how a flat back convex front flat side ( single axis ) lens could square the bean in such a short distance..........of course it is very tiny at the facet so maybe there is room, I know there's room to reduce the divergence of the fast axis yielding a line/bar shaped beam but to square it would mean placing the FAC further away so the faster diverging fast axis can catch up to the junctions length........and as tiny as it is to start there may be enough room, but I do see horizontal and vertical aberrations around the image of the squared beam which doesn't really mean anything, mostly I have not set one up myself and it seems like there's not enough space but either there is or the backside of the squaring FAC may be concave......just thinking outloud and wondering how much bigger the squared beam is after a standard coli lens such as G2 or G8 and wondering if the linear might actually be better, will have to wait and see but I hope its as awesome as it can be, 1w of green in a tight square beam would sure sparkle in the night air :D
Note the Hamamatsu fac lenses all have focal lengths under 1mm. They won't catch all of the beam if set further from the diode. They are I think plano-aspherical as indicated by the drawings.
 

RedCowboy

Well-known member
Joined
Jul 10, 2015
Messages
10,973
Points
113
Cylindrical pairs are used to circularize a laser's beam. If the objective is to not do so than one lens can be use to beam shape.

Cylindrical pairs are used to reduce divergence, the beam may or may not be circular but prism pairs are often used to circularize, basically a cylindrical pair is a beam expander that acts on only one axis, they can also be used to focus or expand light in one axis only or used for any purpose you want to use them for, but there not only about circularizing, if used to expand they are in fact un-circularizing.




Note the Hamamatsu fac lenses all have focal lengths under 1mm. They won't catch all of the beam if set further from the diode. They are I think plano-aspherical as indicated by the drawings.

The fact the drawing shows plano/flat on the input is something I was talking about, why are you telling me this ?

The output side looks convex but could be aspherical, it's not much of a drawing to see that much detail, why are you telling us this ?

Do you just like to quote from what you read without understanding it ? To quote terminology definitions out of context ?
 
Last edited:

steve001

Well-known member
Joined
Jun 3, 2007
Messages
2,517
Points
113
Cylindrical pairs are used to reduce divergence, the beam may or may not be circular but prism pairs are used to circularize, basically a cylindrical pair is a beam expander that acts on only one axis.





The fact the drawing shows plano/flat on the input is something I was talking about, why are you telling me this ?

The output side looks convex but could be aspherical, it's not much of a drawing to see that much detail, why are you telling us this ?

Do you just like to quote from what you read without understanding it ?
You said this.
but either there is or the backside of the squaring FAC may be concave.....
My mistake.
I wasn't soley using that drawing. The photos coroborate the Hamamatsu drawing being plano-aspherical. It's plano aspherical because the radius of curvature becomes greater further from center. This lens is "U" shaped compared to a plano-convex which would have a gentle radius of curvature like this
"("

Could you explain this?
basically a cylindrical pair is a beam expander that acts on only one axis.
 

RedCowboy

Well-known member
Joined
Jul 10, 2015
Messages
10,973
Points
113
" Basically a cylindrical pair is a beam expander that acts on one axis. "

That's my definition, you likely won't find it online, that's how I often use a c-lens pair.

The plano concave cylindrical expands one axis of the beam and the plano convex cylindrical focuses the one axis after expansion resulting in reduced divergence, much like a beam expander for one axis, that's my non Webster's personal observation.

-------------------------------------

I will yell you my concern with the square output FAC modified diode, I am concerned it may produce a wider/larger spot at a given far field distance with our usual array of M9x0.5 barreled lenses than the linear output FAC modified diode and I know Chris bought several for a project, I am thinking the linear output FAC modified diode may produce a smaller spot far field with our normal array of coli lenses and I am waiting before buying more myself, the divergence listed on the sales pages are identical IINM
 

CDBEAM777

Well-known member
Joined
Feb 25, 2010
Messages
1,648
Points
113
Well...Quite a lively conversation !! SO...We must ask ourselves...." Why were these FAC lenses added to any multimode diode " ???? What was/is the final desired engineering outcome ??? What is the application ????? Surly...Hundreds of thousands of $$$ were not invested so that we may enjoy reduced.....or Zero Bar geometry in our HH applications !!! HAHAHA....That MAY be a unintended coincidence….and I am hopeful that it is....
I have NO idea what the final application is for these FAC corrected diodes ???? But....a commercial application involving thousands of diodes would likely be the guess !!!

Now....let us add " Parallax View " to this debate....!!! When we view the Beam Propagation of an uncorrected NUBM044....as it travels out into the night sky ( Never do this !!!.....because ….Sure as SH!T....an airplane will Pop into existence approx. 0.3 seconds just before one turns the beam on !!!! DIRECTLY in front of your Beam ) …...What do you see ???? Basically a beam !!! NOT a Fan/Bar...one see's a BEAM !!!!.....and this is because Human Parallax View comes into play....SO...What is my point ????

" Parallax View " is a great Physiological aspect of Human eyesight !!! ….It does a perfect job of making a less than perfect Gaussian profile beam. ( Where X does NOT equal Y )...look really good/Beamlike.....at Infinity focus !! SO....what we are really after ????

IMNHO...we are after the perception of a fairly equal divergence....SO...X =Y divergence...as close as possible...in the "Medium Field".

Now...you will ask....WTH is the " Medium Field " ???? ....Well....I would say it is the distance between the Nearfield and the LOS ( Line of Sight ) …..SO....From the HH output....to how far our unaided Eye can see....It is this distance I call the " Medium Field ". I speculate that the FAC will deliver..... the perception....that X=Y in the Medium Field… Just my SWAG....We will see shortly !!! Pass the Popcorn !!!

CDBeam
 
Last edited:




Top