Possible protection for Laser Speed Guns

[Paul Szilard - Australia]

Here is the problem:

 

The police are now using hand held laser speed guns to measure your speed, here in Australia. I got done a few months ago, which cost me $234!

 

I have spoken with a guy that sells radar detectors, and he told me that the police are trained to try to aim the laser into your headlight, as the beam bounces across from one side and then the other and produces a strong reflected signal which the police device can use to calculate your speed.

 

Now if we could deploy a headlight protector, which allows light from the headlight bulb to come out, but prevents REFLECTED light (that is light which originates from in front of the bike), to reflect back, then we have a reduced risk of being measured.

 

Such a thing does exist! It is a CIRCULAR POLARIZER. You can test this with a circular polarizer off your digital camera, however for the headlights we need something inexpensive and cut to size film.

 

To demonstrate the effect, take a shiny metal object such as a coin, and place it on the table where light strikes it (you can use a torch if need be). Then place a circular polarizer on top and check to see if the coin is still shiny or dark. Now flip over the circular polarizer and you should see it change from light to dark, or vica versa. Therefore, it matters which way round you apply the filter.

 

Now imagine that instead of the coin, we have a headlight reflector, and instead of the torch, we have a laser gun. If we correctly mount the polarizer, we can greatly reduce the reflected intensity and thus detectability.

 

I have been Googling for sourcing this kind of film and it ain't cheap. Around $90 for a sheet 12" by 8" which should do two big headlights, like the RT's.

 

I am planning to buy some and see.

 

Your comments are invited...

[Quinn]

I'm curious to know how you'll test the effectiveness on the bike.

 

---

 

 

[Albert]

I believe the Klingons tried this ( Cloaking Device). As I recall, the Federation wasn't fooled.

[tallman]

 

 

Someone who needs a cloaking device.

[Danny caddyshack Noonan]

There's usually another way to get readings for doppler shift. All they need is a reflection, if it isn't coming off the headlamp, any other part of the bike that reflects that wavelength will suffice. Question is, does the detector give you enough time ro roll off and slow down before they get a signal back?

 

[markgoodrich]

I don't see how this will work. My understanding of polarizers is they polarize light passing THROUGH a medium (filter). I think what you are seeing with the "dark" coin is light coming back through the filter is polarized, not light reflected off the surface of the polarizer. I suppose the film could be applied in such a manner that the laser would pass through the filter and the return bounce would be polarized, but I still don't see how it's going to help.

 

But then, my understanding of, say, electricity, is that it is magic, so wait for a brainiac to respond.

[Penforhire]

Seems to me that even if it works there may be enough reflected signal back to the gun where the laser strikes non-headlight regions of your bike.

[Paul Szilard - Australia]

Fortunately we are not up against the Federation. Although if they had warp factor travel, I would hardly think that they worry about traveling over 50kph.

 

You can't ever get 100% cloaking and I wasn't suggesting that, but just try this little experiment: park your bike at night, facing a white wall but some distance away, then use a laser pointer and shine it at different parts of the bike and watch on the wall how much of the laser beam is reflected.

 

Here is a little diagram:

/|
/|                    
/|           x ...>....//-=\       
/|                    o    O
/|

wall        you  laser  bike

I am sure you will be able to see that the reflected light is by far the greatest, when you shine your laser into the headlight.

 

The speed gun is the same, except they use infrared laser.

 

The aim of the exercise is to minimise the reflection. Once I get a circular polarizer film, I can try this and even take a photo (must set camera to manual exposure, otherwise the comparison is impossible.

 

Alternative approach could be using a light meter to measure the reflected light intensity. I do have a hand held meter so may be able to do it. Only thing so far I haven't got the polarizer film.

 

Anyway, anything that can significantly reduce the risk of being booked, is worth investigating, IMHO.

[Boffin]

There's usually another way to get readings for doppler shift. All they need is a reflection, if it isn't coming off the headlamp, any other part of the bike that reflects that wavelength will suffice. Question is, does the detector give you enough time ro roll off and slow down before they get a signal back?

 

Laser speed detectors use a pulsed laser and use the delta-time between reflected pulses to calculate the speed - the speeds we operate at are too low for Doppler shift at light frequencies to be easily detectable.

 

What can be done is to carry a laser detector and to minimise the reflected strength of the laser light. A circular polariser may work but a better way is to apply a coating of IR opaque paint, that is clear at visible light frequencies such as this. Note: I have not tried this paint but I know the technique works. In this application the paint would adsorb some IR on its way to the reflector and some more on the way back. Used in conjunction with a detector you should be able to reduce your speed before the laser gets a lock. This has an advantage over a pure laser jammer - such as some active IR garage openers - insofar as the cop eventually gets a lock so is less likely to pull you for having a jammer.

 

BTW, I have used a laser speed detector as part of my day job and was able to clock my bike at 30mph whilst it was parked in the bike-shed. (sorry I am not allowed to tell you why this happens)

 

Andy

[Paul In Australia]

Paul

Technically I have no idea if this will work on not, But it would only delay a lock on it appears. As Laser detectors are illegal where you are ( actually in bigger poo for using one than speeding) it probably is not going to be any use in the real world. Remember the LEO's now mount them in the grilles etc in unmarked cars and motorbikes. They will get you anyway iMHO.

best regards

Paul

[ratfink]

Here is the problem:

 

The police are now using hand held laser speed guns to measure your speed, here in Australia. I got done a few months ago, which cost me $234!

 

I have spoken with a guy that sells radar detectors, and he told me that the police are trained to try to aim the laser into your headlight, as the beam bounces across from one side and then the other and produces a strong reflected signal which the police device can use to calculate your speed.

 

Now if we could deploy a headlight protector, which allows light from the headlight bulb to come out, but prevents REFLECTED light (that is light which originates from in front of the bike), to reflect back, then we have a reduced risk of being measured.

 

Such a thing does exist! It is a CIRCULAR POLARIZER. You can test this with a circular polarizer off your digital camera, however for the headlights we need something inexpensive and cut to size film.

 

To demonstrate the effect, take a shiny metal object such as a coin, and place it on the table where light strikes it (you can use a torch if need be). Then place a circular polarizer on top and check to see if the coin is still shiny or dark. Now flip over the circular polarizer and you should see it change from light to dark, or vica versa. Therefore, it matters which way round you apply the filter.

 

Now imagine that instead of the coin, we have a headlight reflector, and instead of the torch, we have a laser gun. If we correctly mount the polarizer, we can greatly reduce the reflected intensity and thus detectability.

 

I have been Googling for sourcing this kind of film and it ain't cheap. Around $90 for a sheet 12" by 8" which should do two big headlights, like the RT's.

 

I am planning to buy some and see.

 

Your comments are invited...

 

I tried this....oxyacetylene torch, coin was a lump and yes very dark.

 

Polarizing filter was vaporized.

[DewNMoon]

Well you could be "observant" and look for the LEO pointing the device at traffic being they have to target you.

 

Or try $$ this stuff

 

http://www.radarbusters.com/laser-jammers/laser-jammers/6524+6527+4293856175.cfm

 

http://www.radarbusters.com/radar-detector-accessories/laser-veil/6524+6531+4293663457.cfm