laser flares- is the fan made by a filter?

[tim_ber]

http://www.rescue-flares.co.uk/How_to_use_Rescue_safety_flares.html

Is the main difference between a laser pointer and the laser flare that a laser flare has a filter on the end to create the "fan" like pattern the web site talks about?

In other words it is a 7mW laser, waterproof, but with a divergence filter? And therefore possible to make / obtain for less than £70?

In fact I am soon to test a brand new green laser with a filter that I obtained for £4 inclusive - first sights (not long distance yet) appear to offer a large visual area.

 

[elton]

I don't know, but I'd use a rotating mirror, or a pair of mirrors on speaker cones fed with signals designed to create the pattern.

 

[pteron]

It's a cylindrical lens. Fire a laser at it and it forms a fan.

Must be possible to make for less than 70 quid.

I wouldn't use mirrors - who wants moving parts when you can do it without?

 

[VicS]

The one I like the look of is the ODEO FLARE
Unlike the one above it is omnidirectional so does not have to be aimed at any would be rescuer.

A little more expensive than £70 unfortunately.

 

[tim_ber]

job done

Well, I've just finished making my laser flare from a laser pointer (not waterproof yet), but has a superb flare/cone pattern by hacking a few bits from the workshop. Total cost £5 I reckon. Don't think it is 7mW (therefore range may be compromised), but it will do me for now and will be in my pocket when I'm in the Solent this Jan and Feb. Other pocket will have mini flares in it, but not a huge fan of explosives.

It is indeed much better than a laser pointer (as far as being able to attract a third party's attention) as the website points out, but can easilly be made for way less than £70.

 

[elton]

It's a cylindrical lens. Fire a laser at it and it forms a fan.

Must be possible to make for less than 70 quid.

I wouldn't use mirrors - who wants moving parts when you can do it without?

I don't believe it can be done without moving parts. If you think otherwise then please explain how it's possible to create a 6000 ft wide solid cone of light without using a massive power source.

In fact the one VicS pointed to states

Continuously lit lasers rotating at variable speed from 240 RPM downwards

 

[tim_ber]

The one I like the look of is the ODEO FLARE
Unlike the one above it is omnidirectional so does not have to be aimed at any would be rescuer.

A little more expensive than £70 unfortunately.

Yes, I read a past thread about that one. Some people highlighted a few issues about it and I seem to remember agreeing with them (in my mind) at the time.

Certainly a few design tweaks I'd like to make to it before I bought one. Going the right way though.

Gunpowder is old fashioned stuff or magnalium powder or whatever is used now (Wessex - another over priced product in my opinion)

 

[Twister_Ken]

but it will do me for now and will be in my pocket when I'm in the Solent this Jan and Feb. Other pocket will have mini flares in it, but not a huge fan of explosives.
.

Hope you don't have to use it, because no-one will recognise it as a distress signal.

 

[Woodlouse]

I don't believe it can be done without moving parts. If you think otherwise then please explain how it's possible to create a 6000 ft wide solid cone of light without using a massive power source.

In fact the one VicS pointed to states

It's not a solid cone of light. All it is is a laser diode that, instead of concentrating all of the light to a small point, is diffused at an angle of roughly 3.75 degrees. All anyone looking at it would see is a very bright light source, but they wouldn't be illuminated.

 

[maxi77]

Well, I've just finished making my laser flare from a laser pointer (not waterproof yet), but has a superb flare/cone pattern by hacking a few bits from the workshop. Total cost £5 I reckon. Don't think it is 7mW (therefore range may be compromised), but it will do me for now and will be in my pocket when I'm in the Solent this Jan and Feb. Other pocket will have mini flares in it, but not a huge fan of explosives.

It is indeed much better than a laser pointer (as far as being able to attract a third party's attention) as the website points out, but can easilly be made for way less than £70.

I would have a slight care using cheapo lasers, though they are supposed to be nominally eyesafe the QC on items that cheap is slight, and it is not uncommon to get a unit that is not safe.

It is the testing and quality control that takes the cost of something safet to use up over £70. I certainly have only one pair of eyes and have no intention of putting them at risk with cheap potentially blinding lasers.

Personal choice but that is mine.

ps, until there is a proper standard that can be recognised clearly from a helicopter no rescue helicopter pilot will go any where near an unkown laser source, for the pretty obvious reason he values his eyesight.

 

[elton]

It's not a solid cone of light. All it is is a laser diode that, instead of concentrating all of the light to a small point, is diffused at an angle of roughly 3.75 degrees. All anyone looking at it would see is a very bright light source, but they wouldn't be illuminated.

So how diffuse do you think a milliWatt laser is going to be, spread into a 3.75 degree cone over several thousand metres? They don't work like that. They have moving mirrors or prisms. The light is not diffused or spread, it is swept or scanned verically and horizontally in a repeating pattern.

 

[Woodlouse]

So how diffuse do you think a milliWatt laser is going to be, spread into a 3.75 degree cone over several thousand metres? They don't work like that. They have moving mirrors or prisms. The light is not diffused or spread, it is swept or scanned verically and horizontally in a repeating pattern.

Take a look at the product in the original link. The thing is less than 4 inches long, how are you going to fit moving mirrors or prisms into that? The only movement comes from waving your hand about when you hold it. It's little more than a small torch with a laser diode instead of a bulb.

http://www.rescue-flares.co.uk/Rescue_laser_flare.html

 

[maxi77]

So how diffuse do you think a milliWatt laser is going to be, spread into a 3.75 degree cone over several thousand metres? They don't work like that. They have moving mirrors or prisms. The light is not diffused or spread, it is swept or scanned verically and horizontally in a repeating pattern.

At the end of the day the real limit on power is the irradience per square mm generated at reasonably close range. That is what kills your eyesight. Then there is the problem of the rescue service being able to tell from what they see that the laser you are using will not blind or dazzle them. Just think what happens to your night vision when some one shine an Aldis lamp in your face.

 

[Mistroma]

Signal type

Hope you don't have to use it, because no-one will recognise it as a distress signal.

Do you mean:

a) People expect to see a flare and would ignore a laser.

If so, then carrying a £70 unit would be equally pointless.

b) Homemade unit output is different from £70 unit.

i) Weaker: It is as OP said that but 5-50mW lasers aren't very expensive so higher power possible at little cost. But that's a matter of range, not recognising as an SOS.

ii) Colour: Not certain viewer would readily see much difference between similar red lasers. Range would be affected in different conditions.

iii) Signal "shape": Both described as fan shaped (simple rod type lens?). Simple lens would probably output a Gaussian distribution of light wrt angle. So output intensity would drop sharply at towards each end of the fan.


Just wondering? My own view is that public tend not to ignore big light in sky but might not put much weight behind a flashing light. However, the laser would alert a S&R to your location and they aren't a one-shot deal.

I haven't had time to look for the specs. of the £70 unit but will try to see if they specify performance.

 

[Twister_Ken]

Do you mean:

a) People expect to see a flare and would ignore a laser.

Yes. The laser 'flare' is not a recognised distress signal by any authority, nor - I suspect - the general public. Fixed and flashing lights are the norm for nav lights and buoys, not for distress.

If so, then carrying a £70 unit would be equally pointless.
Yes

.

 

[Woodlouse]

I don't think they're selling this device as a distress signal for raising the alarm. I think it's intended to reveal your position once you've sighted the rescue services that are looking for you after being alerted by more traditional methods.

 

[pteron]

I don't believe it can be done without moving parts. If you think otherwise then please explain how it's possible to create a 6000 ft wide solid cone of light without using a massive power source.

I don't care what you believe, I told you how Rescue Flares do it.

 

[mikefleetwood]

The "Rescue laser" products have no moving parts - just a cylindrical lens (or similar) to spread the beam on one axis. They would appear to use standard small laser diodes, as in hand-held pointers, etc. Probably about 0.5mW output.

The main problem, as far as I can see, is how does a rescue pilot distinguish these "safe" devices from the beam from a normal laser pointer - which will not be "safe"? The colour and appearance will be the same.

The reason lasers are dangerous to the eye is not just the parallel beam (in otherwords the brightness doesn't change much with distance), but the eye is capable of focussing the monochromatic light onto a very small spot on the retina, causing localised burning and scarring. As it happens, the output from a normal (beam not spread) laser pointer at 0.5mW is not particularly dangerous, especially at distance (there will be some absorbtion and dispersion). The threshold for retinal damage is about 0.5mW, and the blink reflex will kick in before any damage can be done - which is probably why such devices are legally available.

However, any bright source of light will screw up your night vision, which is not a good thing when flying a helicopter!

 

[maxi77]

The "Rescue laser" products have no moving parts - just a cylindrical lens (or similar) to spread the beam on one axis. They would appear to use standard small laser diodes, as in hand-held pointers, etc. Probably about 0.5mW output.

The main problem, as far as I can see, is how does a rescue pilot distinguish these "safe" devices from the beam from a normal laser pointer - which will not be "safe"? The colour and appearance will be the same.

The reason lasers are dangerous to the eye is not just the parallel beam (in otherwords the brightness doesn't change much with distance), but the eye is capable of focussing the monochromatic light onto a very small spot on the retina, causing localised burning and scarring. As it happens, the output from a normal (beam not spread) laser pointer at 0.5mW is not particularly dangerous, especially at distance (there will be some absorbtion and dispersion). The threshold for retinal damage is about 0.5mW, and the blink reflex will kick in before any damage can be done - which is probably why such devices are legally available.

However, any bright source of light will screw up your night vision, which is not a good thing when flying a helicopter!

There are a number of factors which impact on eye damage, wavelenth is one, you can have relatively eyesafe lasers at much higher powers if you pick the right wavelength although none of those wavelengths are visible. then there is the actaul irradiance on the retina, and that is from a combination of output, beamwidth, wavelength and pulse length. Blink can provide protection from CW lasers as you blink before the main beam hits the pupil, but I would be reluctant to rely on that for my own eyes. Blink is much less effective when the laser is pulsed.

Finally remember cheap laser diodes can vary greatly in output because the processes are not optimised to keep costs down and they are not tested individually again for cost reasons. Many do give a higher output than they are rated at which is why those cheap pointers are potentially dangerous.

And yes a laser even an eyesafe one can destroy your night vision for a long time, it can even dazzle you for long periods in daylight.

 

[tim_ber]

Agree with a lot of the above.

The function of it for me would be to get those that just knocked me off the boat to locate me again (figuring that I can see their mast lights easier than they can see me) - not for helicopters etc to locate me.

I'm spending some time on a big boat this winter with a large crew and one bod falling overboard is different from one bod out of 4 falling overboard (you usually notice one mob out of a small crew pretty quickly).

Anyway, I'm sure that is another thread altogether.

Thanks for laser info.