Advice on large long distance scanning onto white cliffs

[jammah]

Hi All!
Today something interesting fell into my lap one of the event orginisers for the Large New Years festival in my home town saw my laser and is interested in working with me next year.
Amongst other things he had a fairly interesting project in mind Our town is Fairly small with around 30,000 people we get around that same amount coming to the three to five day long festival to accomidate the massive influx they setup large temporary camp grounds north of the city on the beach
This guy is wanting to project basic block lettering onto the white cliff faces of young nicks head from the campgrounds
ill add pics that should illustrate this better
Im obviously fairly new to all of this But in NZ Im one of the few who has anything to do with lasers and I would love to be involved in such a project!
SOOO I thought I would ask your wisdom and thoughts!

Can It be done?
How Far can a projector fire ? ( Unless its done from a boat its about 3km away)
How Much POWER

I bought a 8 x array off bbe would 8 m140's be enough ????

Any thoughts or input would be really appreciated!

Oh and also I should note the cliffs and the area behind is private farmland there is no houses or public access so it will not be firing into anyone

Thanks in advance

James

[Jem]

Hi James

3Km away is a bit of a tall order. You'd need *really* good divergence from your laser modules and even then the text would have to be huge to be readable. Assuming a 1mrad divergence the beam is going to be 3 meters diameter at 3Km. Oh, and think really hi power as well. Also, think about movement and how it's magnified over distance, have you ever looked through high powered binoculars at a distant object? Just not feasible in my opinion. I think you need to be getting much much closer to those cliffs, say ~100/200 meters or may be even less for a standard laser projector. Is there no beach in front of the cliffs where you could set up?, even though that may be close to the cliffs you could use wide angle scanners, the text would be readable and power requirements would be less.

You have a PL member in Rotarua who is also a Pangolin dealer, his PL name is Pitts. His personal name is Ray. If you contact him he can perhaps advise the best way of going about this.

Sorry to pee on you bonfire, but I think you need to take the stable boat option (if there is such a thing) or even better get a rig on the beach ;-)

[sbk]

Hi James,

I believe you could easily do that projection at 3km distance, with lets say as little as 200 watts laser power

Have a look, these guys did something similar : http://www.youtube.com/watch?v=VmdLPcYrTsU

[Laserhobbit]

Hi james,

In my first round of being involved in laser shows in the 80s this was one of the requests we seemed to get time and time again. I have to say I have done similar in both the UK and also quite a few times in South Africa and also in Brazil. BUT, and here I am sorry I have to agree with JEM, with no bonfire extinguishing meant. These were the most difficult shows we ever did. But if its an opportunity here are a few pointers:

1) Forget the idea of projecting from a boat, it is just not stable enough and just won't work

2) You must try and scan as close to the cliff as possible with the widest possible scanners. so forget any scanner you would normally use in their normal tuning. We used to use CTs with the scan amp setup for the widest it would scan.
Forget about scan rate being 30K. I have had to run galvos at as low as 3 or 4K to get the angle we needed. More commonly this was about 10 -15k so think about VERY basic text and no really complex shapes. We even used to sacrifice a bit on divergence and use optics to increase the apparent scan angle, but this needs a really low divergence beam

3) Forget about multi colour, unless you are using really high power. Use green and make sure your power is as high as you can get


4) Think about using gas lasers the beam quality will more than make up for the increased complexity. We used to use 2 SP171s or a SP921 for this type of thing.

BUT the good news is it can and has been done, just needs careful planning and a few tests beforehand to check the kit you plan to use looks good. MY advice, scan from no more than 1km, use gas lasers 15w minimum and it may look Ok. I admit I'm an old gashead and so the gas lasers may seem old hat, but the beam quality helps soooo much with this type of thing. First things first it needs to have a trial to see if it possible with the kit you can get hold of. Just using a stacked solid state array and DT40Ws in a boat is unlikely to really work.

Just my 10p and I am sure other PL members will also have advice which may be different. as it is one of those gigs which seems simple until you try it.

Cheers

Steve

[jammah]

cheers fellas I certainly diddn't think it would be easy
really appreciate your help
looks like I have MUCH more homework
I think Ill Go assess the beach right in front of the cliffs, try and get an idea of how much room I have

It may be a case of too hard basket, at this stage it was just an idea he had

and I said I would look into it for him

I must admit a project like this does seem very interesting I guess it depends how deep their pockets are

thanks again guys

EDIT: in saying that 30,000 people at $200 to $400 ticket price per head maybe they are

[Jem]

Thinking a little more about this, I reckon it could be done from a boat, but you'd have to use a gyroscopic stabilised platform to mount the laser on. I guess that'd probably blow the budget though even before you started to think about lasers and their power requirements .

Hehe... I can just imagine trying to run an SP171 on a boat . Well, you'd not be short of water, it'd just be the wrong type. Better add a desalination plant into that budget as well as a decent sized 3 phase generator

[andy_con]

2x 8w opsl greens = about £40k

[White-Light]

I think Ill Go assess the beach right in front of the cliffs, try and get an idea of how much room I have

Should be obvious but don't forget the tides!

Assuming the beach and access is uncovered at all states of the tide, its worth buying a tide timetable for the year, they're usually only a pound or two and its worth checking the tide forecast for the day in question to check for spring tides. Also, don't forget to allow for how the weather can affect all of this - bad weather can cause surges. Last thing you want is for you or your equipment to become swamped or worse...

[norty303]

Don't forget that you can do quite extreme geometric correction to images, so you do have the possibility of scanning from further along the beach but closer to the target. Of course, the downside is that the image brightness and divergence will vary across the image due to the distances involved. Again, you could correct the brightness part with some horizontal shading.

Building a scaff platform on stilts would be both secure and also afford you the luxury of being able to place it in the water (at appropriate height for tide!) and more in line with cliffs

[laserdj]

www.youtube.com/watch?v=AXEQjdbi7Aw&hd=1

This is a 5W head, from around 400m away... (the biggest tree is around 45m high!)
It´s a Viasho, short cavity DPSS, so not a great divergence...
I think you can get it done with more than one green projector, or a LS... contrast with the surface must be great since it will be viewed from 3km away.

Cheers