Long Distance Laser Night Vision Flashlight

There are many infrared LED night vision Instructables but their biggest shortcoming is a lack of distance.  The range is limited to about 5 metres or so.
This Instructable uses an infrared laser to massively increase the range up to 100m (300 feet) or more.

Any laser commands respect.  Almost any laser has the ability to cause permanent eye damage.
Special care must be taken with this project.  Not only is the laser used capable of causing instant eye damage but because it's invisible there is no blink reflex and you won't even realise until it's too late.

Here are some dos and don'ts that MUST be followed if you attempt this project.  I take no responsibility for any injuries!

DO wear proper protective laser goggles when testing.  Make sure they filter the wavelength used by your laser and are in good condition.  Yes they are expensive but your eyes are even more so.

DO disable the laser when not using it:  turn off, use key lock if it has one, remove battery.

DO keep it away from children.  In fact I would go as far as to say treat it as you would a firearm.

DO NOT look directly at the beam or point it at anyone else.  Also beware of reflections off shiny objects.

• an infrared laser.  Mine is a 1000mW which is very powerful for a handheld laser.  They can be quite expensive too so it pays to shop around.  I was lucky to find one on a Chinese web site a couple of years ago for about NZ$50.  Another way to obtain an infrared laser is to convert a green laser which uses an IR laser diode.
• a lens mount.  I recovered one from a broken web cam but they can also be found on Ebay.  They are pretty standard and called a CCTV S-mount.  The thread is M12x0.5
• a CCTV lens to suit the lens mount.  This spreads out the infrared light making it a spotlight and rendering it safe at a distance.  These can be found cheap on Ebay or DX.com.  A 16mm focal length produces a 20 degree field of view.
• pipe fittings to suit.  I used a 25mm to 20mm reducer and a 20mm cap
• possibly some o-rings and tape
• a drill (preferably a drill press)
• hot glue
• safety goggles that filter infrared
• a night vision device.  This could be as simple as a converted digital camera or a full-blown image intensified night vision scope.  I used the former since I can't afford the latter!  (It also makes it easy to take photos for this Instructable!)

This is fairly straight forward.  The idea is to fix the lens in front of the laser using the plumbing parts.  the pictures tell the story better than words.
I drilled a hole in the centre of the cap and fixed the CCTV mount into it using hot glue.  Try to get this as centred and straight as possible.  a drill press helps a lot here.
I used a couple of rubber o-rings and some insulation tape to get a firm fit over the laser body.  The whole build is very solid and won't easily come apart -- important for safety!

The pictures tell the story well.  The left hand side is taken with the IR laser on and on the right with it off.

The big question is, is it safe to use?
Yes it is.  You won't need laser goggles if you use it as intended.  This is why:

The measurement for safe exposure to light is called maximum permissible exposure (MPE) and is measured in Watts per square centimetre (W/cm2).
For near infrared wavelengths a conservative safe value is 0.001W/cm2.
How large does the area of the spotlight have to be for the MPE to be smaller than this?
For a 1000mW laser it is 1000cm2 or a 36cm (14 inch) diameter circle.
At what distance does the light cone project a circle of this size?  For a 20° cone this is about 1 metre (slightly more than 1 yard).
I calculated this on a MPE that is safe to look at.  If you take an inadvertent glance closer than 1 metre you won't go blind instantly.  Just don't stare at it for ages!