Cutting sheet at 45 degrees? Fixture?

[Kev Williams]

Sorry Kev, that's dead wrong. Posting your idea on a public forum will not provide you ANY protection at all. If you want to invent something, you should NEVER post it anywhere until you have filed for the patent. The U.S. Patent system is a "First to File" system, not a "First to prove anything" system.

Canada, the Philippines, and the United States had been among the only countries to use first-to-invent systems, but each switched to first-to-file in 1989, 1998, and 2013 respectively.

DEAD wrong? Give me a little credit. Sorry my 90 hour work schedule has been interfering with my law studies...

[Scott Shepherd]

DEAD wrong? Give me a little credit. Sorry my 90 hour work schedule has been interfering with my law studies...

Is there another way to say that what you told people to do is incorrect by 100% and will actually get you in trouble if you were trying to file a patent? Because it was.

[Dave Sheldrake]

To me that sounds like you didn't think it could work and were citing reasons why.

Nooo, I said it will cause abberations leading to scatter, scatter in any ionising beam is dangerous, sometimes minimally so, sometimes very much so. The point of the comment is not wanting to see a nice guy end up setting fire to his cat or wife's furniture or finding himself with a very hot mirror / broken mirror. Point any laser at pretty much any surface and it will reflect, refract or backscatter, white paint for example in the home has been responsible for eye damage in the groups where people use small 1w 532nm lasers but at least they have a blink reflex to protect them, the human eye has no blink reflex to IR lasers so by the time Bert,Bill or Harrys uber death ray has gone awry it's usually too late to help them.
If I believed or had a reasonable suspiscion that the angled mirror idea wouldn't work I'd have simply said "That won't work" and provided reasons why.....I didn't, I simply said it will cause abberations and scatter.

Having someone spend time making certain their tube is perfectly level, when it does't actually matter, does not help them.

Then go waste a few days reading up on Phase Cancellation, Uncontrolled Mode Changes and the effects of Multi Mode Laser Beams in industrial and semi industrial environments, maybe a look at Professor Shaol Ezekials series of books and lectures may help or some of the printed / posted works by Dr Sam Goldwasser in understanding the effects. Modelling it out in 3D also requires taking into account non linear abberations caused by any reflective surface's effect on a laser beam as well as the base mode of the beam, granted at TEM00 the effects of having a tube out of line won't be noticed but as yet I haven't seen any lasing source outside of a lab approach a single mode TEM00 beam profile.
Another source of useful reading is the published works around the NIF and the methodology they used when aligning resonators. In reality a laser can be pointed at a lens and fired and it will cut, however when you are dealing with the close to minuscule powers of small format lasers anything that sucks those photons is important, losing 2% on a 7kW resonator isn't going to be noticed,losing a base line of 2% on a 30 watt RF tube can make the difference between a job working and failing.

At the very least maybe some additional care will be taken in the future with regards to expert advice.

At no point have I said or suggested what I offer is expert advice, if you want real experts I can name 6 to 10 people easily that make what I know about lasers seem like chump change, that said if I'm going to have to write half a books worth of information down to justify and explain every post I make then it's just easier for me not to post. If the tiniest detail really is that important then there are many seats of learning round the world that offer courses that can help with that as well as a huge volume of publications at post grad level that will provide details to boil the brains of the most avid learner.

Dave, I hope that I did not come across as disrespectful,

Not at all Paul , although at this point in time I'm leaning toward not bothering with posting here anymore, when Rich takes the time to drag up a post from ages ago about tilted laser tubes that kind of tells me all I need to know.

cheers

Dave

[Scott Shepherd]

Not at all Paul , although at this point in time I'm leaning toward not bothering with posting here anymore, when Rich takes the time to drag up a post from ages ago about tilted laser tubes that kind of tells me all I need to know.

cheers

Dave

That would be a real shame Dave. Don't stop posting because one or two people make comments. Think of the 100's of people that have replied positively to you and your help. Don't punish us for something he did

Besides, if that's all it took, there'd be no one left on the forum

[Rich Harman]

...when Rich takes the time to drag up a post from ages ago about tilted laser tubes that kind of tells me all I need to know.

I give up, but I would like to point out that it was you Dave, that dredged up the subject of tilted laser tubes in post #44 of this thread.

[Wilbur Harris]

Deleted this post because what I wrote about is none of my business...

[Keith Colson]

Not to beat a dead horse here, but I cannot see any optical "scatter". When I run the red targeting laser through the system with the lights off I cannot see any red light other than the target dot. I used to measure optical scatter when I was testing retro reflectors in my last job (miniature digital camera and optical ranging design) and it's very easy to see when it is present. Note that you will not get refraction from a first surface mirror either as you need a change in transmission media to enable that effect. I am meeting my optical scientist friend at lunch today and will discuss this further as I am always keen to learn. He was the one that told me to add the 22.5 degree mirror to the system, a really clever guy.

Dave its funny you mention 1 watt lasers in the house on painted walls. I have a blue one mounted in my lounge amongst many other lights. I scan it using a laser printer mirror. I added a monitoring circuit that shuts the laser down if it is not scanning (unsafe). With a smoke machine I get a blue sky effect, it looks pretty cool.

Cheers
Keith

[Dave Sheldrake]

Not to beat a dead horse here, but I cannot see any optical "scatter". When I run the red targeting laser through the system with the lights off I cannot see any red light other than the target dot.

Red dot is already focussed Keith (or in some cases with diodes just collimated), you can either work with an incident beam or a focussed beam but adding a mirror into the optical train of a laser mid focus causes scatter given that the reflected beam will always travel at an equal angle to it's initial. True you won't get refraction from a first surface

Remember coherent laser light and ambient light (as in the case of photography and telescopes) are two very different animals, if not none of us would have thousands of $$$ worth of resonators, we would all just being using lots of LED's

Dave its funny you mention 1 watt lasers in the house on painted walls.

Got a couple of programmable galvo display lasers here great fun when the day job gets tedious and drives my cats mad I still have the ocular limits papers here somewhere from my last LSO course, it's quite surprising how little it takes to do permanent eye damage

A little bit of useless information, a 1 watt blue laser (445nm) shone into space can be seen with the naked eye by the crew of the ISS

cheers

Dave

[Rich Harman]

but adding a mirror into the optical train of a laser mid focus causes scatter given that the reflected beam will always travel at an equal angle to it's initial.

If the reflected beam always travels at an angle equal to it's initial, how does that lead to scatter? (this is my original question BTW) Scatter would be a beam being reflected in an undesired way - reflecting at the same angle it entered is what is desired.

[Dave Sheldrake]

see my earlier reply Rich, it's a gaussian curve once it hits the focal lens, making changes to a part focussed beam changes the profile of the beam leading to abberations and scatter. Similar in some ways to fitting a meniscus lens lens upside down, a lens fitted backwards will cut and in some cases will appear to have a longer focal length but in reality all it is doing is scattering the beam giving a slightly larger spot and strays providing the illusion it cuts better (or deeper).

It can be done using curved (convex) mirrors to re-profile to some extent but the distances involved mean needing a VERY accurate set of spacings (much like a 3 lens collimator does)
This is the big difference between laser optics and visible optics, the curved nature of the beam profile and requirement for the cleanest modes available is what makes it so dang awkward to get right, if you work with the incident beam as far as possible you are dealing with a *rod* of light, that can be manipulated by a 1,000 different methods before hitting the focal train but once you get into the focal train the nature of focussed lasers makes things that much more difficult as any movement (such as heat expansion) moves the relative position of the reflecting surface in relation to the focal state of the gaussian curve.
If the part focussed beam was just a simple V shape then no problems and Keiths idea would work without any problems.
It's the fundamental reason on a lab laser everything that needs to be done is done before the final focal modification even if there are other optics like expanders / combiners etc in the train.

cheers

Dave

[Bill George]

Well its clearly working in the initial tests, but just wondering long term IF the highly focused beam will burn a hole in the mirror or at least make it dark enough to render it useless.

[David Somers]

Dave and Bill and Rich,

Would it be safe to say that in this case, the problems Dave is referring to are there, but that our laser systems have enough slop in them that the loss is relatively meaningless to us, while in a lab system or a more high power system that Dave has in his business it would be more critical. The important thing here being that Keith's mod is working well enough to accomplish his job and it was a mod that was low cost and relatively low effort. It might be that he needs to keep an eye on his mirror for damage over some period of time. Or maybe things are sloppy enough in our lasers that it wont make a difference? It is an inexpensive mirror to begin with as well so he can enjoy the learning process without worrying about the costs if something goes woof.

Either way though, I would certainly appreciate it if Keith doesn't mind continuing to tell us how his next efforts at mods goes! And if you guys don't mind continuing to debate and discuss what he is finding. It has been fascinating to follow and a great learning experience!!

Thanks Keith!!! And Dave and Rich!

Dave

[Dave Sheldrake]

it's a gaussian curve once it hits the focal lens

To clarify...once it EXITS the focal lens

[Bill George]

I guess my question might have be interpreted as being critical, was not intended. It was merely wondered out loud if the mirror or any glass mirror could take that focus beam for long? That I why I was wondering early on if one made from metal as a HD platter would last longer?

There are so many experts on here such as Dave sharing their knowledge, thank you!

[Dave Sheldrake]

I guess my question might have be interpreted as being critical, was not intended. It was merely wondered out loud if the mirror or any glass mirror could take that focus beam for long? That I why I was wondering early on if one made from metal as a HD platter would last longer?

The cheapest *glass* mirrors (K2) are pretty poor quality glass with a gold PVD coating, renown for going pop even in 30 watt DC lasers, The Si Glass mirrors again Gold PVD will stand much more (up to 60 watts incident) without too many problems but above that you need to move to either Cu (Gold coated copper) or Mo mirrors. Mo will take 300 watts without trouble but as the resistance to heat increases the reflective index decreases, The cheapest gold glass mirrors have the highest reflective index and the ultra tough Mo mirrors have the lowest...it's only a matter of 1 - 1.5% difference so in real terms not a lot, all of them are in the high 98% + range and once they get slightly dirty the difference in RI really doesn't matter.

My only concern with HD platters would be their resistance to corrosion and possibly heat distribution as I understand they are a lot thinner than the 3mm standard stuff??

Mo mirrors are the beasts, you can drop them from low orbit and they just don't break

cheers

Dave