Plasics and lasers

[swamidog]

to clarify, some laser modules have adjustable focus. if you're projecting your laser through optics (such as lumia wheels, or other scan through effects), you want to make sure the focal point of the laser is not on the scan through effect or it will burn, even at low power.

project the laser as far away as you reasonably can (even 30-40 feet is helpful) and adjust the laser focus so the projected laser dot is as tight and small as you can make it. this is called "far field" or "infinity focus" and achieves two things:

1) it lowers the overall divergence of the beam.

2) it increases the initial size of the beam so you'll have less energy density on your scan through optics.

most commercial laser modules will already be focused for infinity, but if you build your own or buy modules from other forum members, it would wise to check focus.

Thanks Swamidog,
Just to be clear, if I am controlling the laser via software for example I should widen the beam and aim slightly off angle instead of smack dab center. -I get the concept of bringing the focal point back but with a camera it's a little bit different since you are dealing with an adjustable lens.

[The_Doctor]

Given how much can be had for sharp lumia patterning by focussing fairly tightly on the distorting optic, it pays to test empirically. If the tightest scattering you want will sit still when the optic sits still, you're in business. If it drifts under these conditions, then slight melting is implied. Empirical tests will show whether this is recoverable, or permanent. I didn't try many distorting optics, but what I did try suggests that making the beam diameter any less than about 0.5mm on the optic gets no useful sharpening of image, and also tends to make the output scatter more widely and uncontrollably too, so that can be used to set a lower limit to beam size on impact.

It's hard to settle this in the long term because unless you can be sure of excluding dust settling on the distorting optic's irregular surface, that dust alone will make a huge difference to how the surface absorbs energy and gets distorted itself further in response. I'd try to avoid plastic for that reason alone, glass will be much safer and more consistent for longer.

Another problem, especially with shortwave light, is that some plastics will degrade and become more opaque, clouding the image and making them more vulnerable to absorbing excessive energy even in other wavelengths that did not cause this problem, so they might still melt in the end.

[Bradfo69]

Thanks Sir Swami... one latte for you at SELEM. I really haven't messed with homebrews so, I really didn't know about their focusing.

[norty303]

BTW, the 40W in the specification is the electrical consumption from the mains, NOT the output power of the lasers, but I guess people have realised that

[Revmutt]

For those of us in tiny apartments without the space for proper work benches and such, I always say bring a pointer into shops that may have old cheap glassware. Textured stuff, Hobnail and what have you are good targets. Small items like shot glasses and candle holders make sense because they come in pairs or more.

For what I'm building I should be able to use both plastic and glass.

[TechJunkie]

For what I'm building I should be able to use both plastic and glass.

Thats what I'm doing now. I crushed some glass into fine shards, then melted them into a clear CD. The type that comes on top of a CD spindle. It looks really cool, and very cheap to produce. I also took a small glass bottle, about the size of a dime, and added some oil, and shards. When it rotated it never repeated the same effect because the glass would slowly tumble in the oil altering the effect. The trouble is you have to run it horizontally for the glass to tumble, so the effect is vertical, but still looks amazing.

[The_Doctor]

Thats what I'm doing now. I crushed some glass into fine shards, then melted them into a clear CD. The type that comes on top of a CD spindle. It looks really cool, and very cheap to produce. I also took a small glass bottle, about the size of a dime, and added some oil, and shards. When it rotated it never repeated the same effect because the glass would slowly tumble in the oil altering the effect. The trouble is you have to run it horizontally for the glass to tumble, so the effect is vertical, but still looks amazing.

Nice. Especially the oil-and-shards jar. That one might work with high power because it can spread the heat and probably stand a lot too. Could be dodgy as hell if it burned or exploded, but you'd need a LOT of heat to do that, and even then you'd get warning before it did it.

Idea: if you could pare tiny shards of acrylic into oil, the heat of a beam might make a kind of lava lamp lumia! NO MECHANICAL MOVING PARTS. Heat from the beam would cause convection to move the shards in the oil. I bet there will be people reading this who want to try it...

[laserlackey]

Idea: if you could pare tiny shards of acrylic into oil, the heat of a beam might make a kind of lava lamp lumia! NO MECHANICAL MOVING PARTS. Heat from the beam would cause convection to move the shards in the oil. I bet there will be people reading this who want to try it...

..... *head kersplodes*.... running off to procure a multi-watt source and jar of oil now