Focus lasers with bending mirrors ?

[mixedgas]

Aspheric mirrors will do this, but the technology to make them is out of the range of most of our Asian optics friends.
Your always on the verge of breaking the glass if you try this in short distances.

The easier way is to run the beam into a large diameter, long length fiber with the right numerical aperture to match the diode.

You then induce "microbends" into the fiber to do mode striping and clean up the beam with a Planters style spatial filter.

As most people can't cleave fiber nor do they own a polishing puck, this falls on deaf ears. I have a paper on coupling seven multi-mode 650 nm diodes into a single fiber. However the optical real estate to do will fit in my 18"x18"x36" projector, not the micro tiny boxes that PLers insist on. Tiny boxes are reaching their performance limits in many cases.

"I cant do it Captain! I can't defy the laws of physics, Sir!"

The fictional character, Montgomery Scott, from Star Trek.

Steve

[The_Doctor]

I saw what RS Components wanted for fibre handling, once. More than people usually want to pay for the latest laser. Definitely beyond me.. As is handling tiny boxes, the older I get... My current mount experiments are tiny, but if that effort fails I'll be buying more bits from Dave.

[planters]

I actually think it isn't that complex. The single mode lasers have a nice beam product, but are limited to extracting their energy from a small volume and so have relatively low power. The multi-modes operate like you clustered numerous single mode diodes together. More volume is utilized and the individual single mode pathways within the cavity run sorta parallel to each other just like what you get when you knife edge a number of single mode diodes to build their power to equal the multi-mode diode's output.

This brings up a tangential point that Steve mentioned. Some of these beam manipulation techniques such as spatial filtering and larger finer adjusting optical mounts as well as beam expansion telescopes require additional space, but the benefit of the higher quality beam that is possible to me seems worth it. I would like to see some examples of beams that push the boundaries for brilliance even if the projectors are less portable.

[The_Doctor]

Well, that's pretty much what I hoped and thought, hence the question. See, I used to think single mode was the only way to go for this, and it seems that my rethink is worth following up with money now. Thanks for the thoughts on this. I was never sure if other things in multimode operation might screw up the quality but it seems to me that even singlemode, without spatial filtering, is fairly messy anyway! So I think I'll be trying some G71 diodes ASAP. (I think P73 might be tougher to handle, and I never liked open cans. Also, most cheap lenses such as I have are optimised for those little 0.3mm thick windows in diode cans so I'll not argue with the makers' intent there..

About spatial filtering, I didn't follow the whole thread closely, having heard of spatial filtering before, but you may well be able to correct me before I waste time on something.. It occurred to be that some 'exacto' type blade might allow easy precision with much shorter focal lengths, so smaller space used. They have a shallow slant, and a very straight edge, so can reduce the demands for adjustment precision if the back of the blade were retained in a groove such that he blade runs along that groove, driven by an optician's screw for extremely fine pitch. Could that combination allow secure adjustment with focal lengths as low as a cm or so?

[Vidal Wolf]

Nightlightdean had a response to bending a mirror in another thread a couple days ago

[logsquared]

Wow! pushing this into the adaptive optics realm is past what I am willing to do. I can say that a simple cylindrical curved mirror placed a focal length away from the source has some benefits over the standard 2 lens telescope. The length away from the source helps ease alignment especially when using multiple knife edged mitsu diodes. The cost could be very low.

[planters]

Wow! pushing this into the adaptive optics realm is past what I am willing to do.

Me too. I think that using higher quality,but standard techniques is the way to go. X/Y diode mounts that allow a diode to sit perfectly centered to the aspheric lens (many of these small molded asphers are 1/100 wave precise), super precise focusing and the willingness to revisit focus once or twice, perfectly centered lens elements and final spatial filtering will give the most cost effective results. Adaptive optics (and I have designed and built real ones) have a high threshold. You need to invest a lot of effort just to bring the quality up to countering the degradation caused by the added complexity. Only then do you see any improvement. This may be justified for an important optical system such as a microscope or observatory telescope, but for a projector you would need a system for each diode. That is unless you included, and this might be more practical, an auto focusing/co-alignment system under the heading of adaptive optics.

[kecked]

the best thing I've found is to use a 2 or 3x beam expander and let it clip the beam. At least in my living room that allows me a pretty tight beam on the wall even from the 445nm diodes. Have not tried the high power reds. I just love the 170mw opnext diodes.

[VDX]

... you can use fiber-optics to 'harmonize' the laser output.

I'm working with fiber-coupled diodes for material processing, but positioning a fiber with 0.1mm diameter directly to the chip is common in other fileds too.

You'll loose the coherency, but collimating and focussing the resuling beam after 'averaging' through the fiber is easy ...

Viktor

[badger1666]

I played around with flexing a mirror so it was slightly concave ,that just made the stripe wider
Tried 45deg and < and the beam just got bigger. But going towards 180deg it did start to improve ,just cant get enough flex on the mirror i have , need to find some thinner mirrors with a bit more flex in them or just not bother sound like a better option and just spend $$$$$$$$ on some single mode and have done with it.