"It detects laser scatter..."
Discussion
A claim made on behalf of the new Road Angel during a conversation with a rather pleasant young lady at the Motorshow yesterday.
I don't own such any such device currently but having passed mobile lasers twice (two different places) on consecutive trips to the office I'm now considering it.
But is this claim true? Surely, any scatter off a vehicle being targetted in front of you is going to go off in any direction EXCEPT behind it. So assuming you're on a fairly straight road, the only way a detector on your vehicle is going to receive any is via a lucky second bounce off a conveniently positioned bus shelter or similar. Chances of that?
Have I missed something or is this pretty much the way it works?
There's very little scattering of IR LASER from LIDAR guns in the real world. Usually the registration plate is the first target, but assume the operator goes for a headlight then you might get some of the beam reflecting off the side of the car in front which you could pick up but with the divergence on the LIDAR beams being so little, I wouldn't rely on this.
As people have already said - if it goes off, you're booked.
As people have already said - if it goes off, you're booked.
erm..............not that daft actually, but I'd like to see one demonstrated to be completely convinced. the Laser is infact modulated a bit like a TV remote control. The LED in a Telly zapper is very low power, and fires at a very wide angle so the beam intensity at the actual telly is extremely low. To make the detector see it at all the zapper modulates the LED (I don't just mean the coding pulses) at about 35-40KHZ. The detector in the telly is nothing more than a radio that uses an IR dependent resistor as the aerial!. The LTI is similar. The laser modulates and the detector can pick this up much more reliably. So, on your laser detector you have a sensitive IR dependent resistor feeding a very high Q factor radio filter, tuned to the modulating frequency of the LTI2020. If the filter is very stable (digital?), you can achieve very high Q factors making the detector very sensitive to an LTI2020. Seeing as it blasts away at 30mW (which is f.......g bright if you've ever seen a 30mW visual laser) you'll get bonnet bounce, road bounce, the lot, even if it's trained on the numberplate, and even through mist in the air.
However, like I said, I'd like to see one working before investing in one!
However, like I said, I'd like to see one working before investing in one!
Ok; my first post here, so please be kind if this is all old hat, or covered elsewhere ( I've had a reasonable look, and can't see it mentioned elsewhere, so here goes):-
All the talk is of detecting/defeating the laser speed measuring apparatus.....what about the health and safety aspects?
The 20mW range mentioned puts the laser firmly into class 3b territory. Which isn't pleasant, for a start - reading from the H&S site they state:-
"Laser products having a level of accessible emission which can be harmful to the unaided eye but generally will not cause injury to exposed skin. Diffuse reflection hazards (ie, those arising from rough surfaces) are generally of low risk."
Preventative measures - "Prevent eye exposure to the beam. Guard against unexpected specular reflections (ie. those arising from shiny, mirror-like surfaces)."
In other words, if a police office is pointing a laser at me, I'd think I'd have fairly good grounds to be unhappy.
I can recall an interview with a police constable saying 'we aim straight between the eyes". Ouch. Now, to be entirely honest, I'd be surprised if anyone did get injured in this fashion; with the power level involved, dwell time would have to be at least a second, and I think this is unlikely to occur in practice...however, as the beam is outside the visible spectrum, you're not going to see it, so the 'blink response' isn't going to help you.
It could be interesting to see what happen if everyone who gets stopped under these circumstances starts rubbing their eyes and complaining of blurred vision...I'd also like to know who the relevant Laser Safety Officer is.
Interestingly enough, the health and safety executive do not make any statements about the safety requirements for class 3b lasers except "These are potentially very hazardous laser products capable of causing severe burns as well as eye injury. Their safety assessment is a specialist area and inspectors are advised to contact HSE or the National Radiological Protection Board (NRPB) for assistance in assessing the safety performance of these types of device."
However, for class 3a (less powerful), they state "Only employees approved by the LSO should be assigned to install, adjust and operate class 3A laser products. Warning signs should be posted in any areas where class 3A laser products are used and to which there is access by untrained people (such as members of the public). Systems of work and their operation should ensure that it is not possible for a person to stare directly into beams or through optical instruments which have not been fitted with suitable filters to protect the viewer. Where practicable, laser beam paths should be located well above or below eye level. Proper account should be taken of hazardous reflection risks." I'd say that all of these would be areas where questions could be asked.
If a member of the public was to point such a device at me, I'd think they'd be in danger of getting a fairly unpleasant fine. Any of the BiB care to comment on what precautions are taken?
All the talk is of detecting/defeating the laser speed measuring apparatus.....what about the health and safety aspects?
The 20mW range mentioned puts the laser firmly into class 3b territory. Which isn't pleasant, for a start - reading from the H&S site they state:-
"Laser products having a level of accessible emission which can be harmful to the unaided eye but generally will not cause injury to exposed skin. Diffuse reflection hazards (ie, those arising from rough surfaces) are generally of low risk."
Preventative measures - "Prevent eye exposure to the beam. Guard against unexpected specular reflections (ie. those arising from shiny, mirror-like surfaces)."
In other words, if a police office is pointing a laser at me, I'd think I'd have fairly good grounds to be unhappy.
I can recall an interview with a police constable saying 'we aim straight between the eyes". Ouch. Now, to be entirely honest, I'd be surprised if anyone did get injured in this fashion; with the power level involved, dwell time would have to be at least a second, and I think this is unlikely to occur in practice...however, as the beam is outside the visible spectrum, you're not going to see it, so the 'blink response' isn't going to help you.
It could be interesting to see what happen if everyone who gets stopped under these circumstances starts rubbing their eyes and complaining of blurred vision...I'd also like to know who the relevant Laser Safety Officer is.
Interestingly enough, the health and safety executive do not make any statements about the safety requirements for class 3b lasers except "These are potentially very hazardous laser products capable of causing severe burns as well as eye injury. Their safety assessment is a specialist area and inspectors are advised to contact HSE or the National Radiological Protection Board (NRPB) for assistance in assessing the safety performance of these types of device."
However, for class 3a (less powerful), they state "Only employees approved by the LSO should be assigned to install, adjust and operate class 3A laser products. Warning signs should be posted in any areas where class 3A laser products are used and to which there is access by untrained people (such as members of the public). Systems of work and their operation should ensure that it is not possible for a person to stare directly into beams or through optical instruments which have not been fitted with suitable filters to protect the viewer. Where practicable, laser beam paths should be located well above or below eye level. Proper account should be taken of hazardous reflection risks." I'd say that all of these would be areas where questions could be asked.
If a member of the public was to point such a device at me, I'd think they'd be in danger of getting a fairly unpleasant fine. Any of the BiB care to comment on what precautions are taken?
Jimmyjimjim....
"..The type of laser used is an infrared semiconductor laser diode. The generated light energy has a wavelength of approx. 900 nanometers, with a beam divergence of 3 milliradians, equal to a beam width of about 3 m (or ft) at 1000 m (ft). Target acquisition times range from 0.3 to 0.7 seconds.
This laser is completely eye safe, meeting FDA Class 1 specifications. This means that you could stare directly into the laser for 3 hours without any harm to your eyesight. The radiated light power on MOST lasers is in the order of 50 micro watts, or in other terms, it outputs only one twentieth the light power of a typical TV remote control, and far less than a flashlight.
Which is why Diffusers using industry standard laser LED diodes are effective against laser guns..."
"..The type of laser used is an infrared semiconductor laser diode. The generated light energy has a wavelength of approx. 900 nanometers, with a beam divergence of 3 milliradians, equal to a beam width of about 3 m (or ft) at 1000 m (ft). Target acquisition times range from 0.3 to 0.7 seconds.
This laser is completely eye safe, meeting FDA Class 1 specifications. This means that you could stare directly into the laser for 3 hours without any harm to your eyesight. The radiated light power on MOST lasers is in the order of 50 micro watts, or in other terms, it outputs only one twentieth the light power of a typical TV remote control, and far less than a flashlight.
Which is why Diffusers using industry standard laser LED diodes are effective against laser guns..."
sorry echo, but need to comment. The wattage of a laser is the actual energy of the light as it leaves the laser unit. By comparison, the wattage of a flashlight is the power consumed by the bulb, and not it's actual light output. The electromagnetic energy given off by a bulb is caused by electrons falling from a high energy state to a low energy state. When the energy fed into the bulb is low, the frequency of the radiation is low (ie heat energy). As the energy input increases the frequency increases until you straddle low frequency visible light (red). you are already consuming a fair ammount of power, but are recieving only a dim glow for light output. More power, higher frequency RED, then Green, the Blue, then Violet then probably POP. Bulb filament melts.
Generally you find that only a couple of percent of energy put into a bulb appears as light, (filaments bulbs anyway) and even this light is very wide band so there's no significant energy peaks. Now back to a laser. ALL the energy is going into just 1 frequency, a bit like a tuning fork. This gives a huge peak of light energy at one frequency (1 colour) which is chanelled into 1 thin beam. a 30mW laser in the visible part of the spectrum would blind you almost immediately. For interest, did you know that a 30W laser (such as a YAG - Ytrium alluminium garnet) is so intense you can actually get a visible flash off the moon with one? (the appolo corner cube that was left there on the sea of tranquility). Get THAT from a 30W table lamp!.
TV remotes are VERY low power by the way.
Generally you find that only a couple of percent of energy put into a bulb appears as light, (filaments bulbs anyway) and even this light is very wide band so there's no significant energy peaks. Now back to a laser. ALL the energy is going into just 1 frequency, a bit like a tuning fork. This gives a huge peak of light energy at one frequency (1 colour) which is chanelled into 1 thin beam. a 30mW laser in the visible part of the spectrum would blind you almost immediately. For interest, did you know that a 30W laser (such as a YAG - Ytrium alluminium garnet) is so intense you can actually get a visible flash off the moon with one? (the appolo corner cube that was left there on the sea of tranquility). Get THAT from a 30W table lamp!.
TV remotes are VERY low power by the way.
bryan35 said:
So, on your laser detector you have a sensitive IR dependent resistor feeding a very high Q factor radio filter, tuned to the modulating frequency of the LTI2020. If the filter is very stable (digital?), you can achieve very high Q factors making the detector very sensitive to an LTI2020.
A very high Q factor filter would not be useable in this situation. The regular incomming pulses would cause the filter to ring, making accurate measurements of time of flight very difficult.
Much more likely that the laser guns are using synchronous detection which provides a huge increase in performance of simple envelope detection.
bryan35 said:
sorry echo, but need to comment. The wattage of a laser is the actual energy of the light as it leaves the laser unit. By comparison, the wattage of a flashlight is the power consumed by the bulb, and not it's actual light output.....
.... a 30mW laser in the visible part of the spectrum would blind you almost immediately. For interest, did you know that a 30W laser (such as a YAG - Ytrium alluminium garnet) is so intense you can actually get a visible flash off the moon with one? (the appolo corner cube that was left there on the sea of tranquility). Get THAT from a 30W table lamp!.
TV remotes are VERY low power by the way.
What a load of waffle.
bryan35 said:
The wattage of a laser is the actual energy of the light as it leaves the laser unit. By comparison, the wattage of a flashlight is the power consumed by the bulb, and not it's actual light output..
Read it again (it's not my text it's a direct quote from a laser manufacturer hence my "") - Where is there a comparison between wattages? There is mention of a wattage for the laser but NOT for anything else?
You also seem to be mixing up milliwatts and microwatts (simple mistake) - the text refers to uW not mW.
echo, where are you getting the stats for the LTI2020? Their website is about as much use as a chocolate teapot; the only reference to output being "class 1" or intrinsically eyesafe.
The actual output could be anything; it's likely to be in the 5-30 milliwatt range though - most laser pointers pump out <1~<3 milliwatts by comparision, 30 microwatts would be a very low power application, jamming/disrupting/confusing such a low power source would be comparatively easy.
A 30 milliwatt laser, (if focused), would certainly blind you within a quarter of a second or so.
A 30 watt laser would easily reflect off the moon.
The dispersal of the beam at range obviously reduces the effect, I suspect this is what allows the class one rating in this case; I most certainly wouldn't stare into it point blank.
Now, the fact that the beam will be widely reduced in power, due to the spread at range, does leave some room for manoeuvre, and the diodes referred to earlier should certainly be potent enough to do something. However, I was reminded of a US gov't idea for Laser jamming (they started research on 'non-lethal' battlefield weapons, and decided using lasers to blind enemy soldiers was worth inverstigating...then decided to look at countermeasures, for obvious reasons) - aerosol sprays. Tried various thing, I can't remember what, exactly, apart from powedered glass. Only drawback is deployment - anyone got a good idea for keeping a cloud of fumes surrounding the car at 80mph?
The actual output could be anything; it's likely to be in the 5-30 milliwatt range though - most laser pointers pump out <1~<3 milliwatts by comparision, 30 microwatts would be a very low power application, jamming/disrupting/confusing such a low power source would be comparatively easy.
A 30 milliwatt laser, (if focused), would certainly blind you within a quarter of a second or so.
A 30 watt laser would easily reflect off the moon.
The dispersal of the beam at range obviously reduces the effect, I suspect this is what allows the class one rating in this case; I most certainly wouldn't stare into it point blank.
Now, the fact that the beam will be widely reduced in power, due to the spread at range, does leave some room for manoeuvre, and the diodes referred to earlier should certainly be potent enough to do something. However, I was reminded of a US gov't idea for Laser jamming (they started research on 'non-lethal' battlefield weapons, and decided using lasers to blind enemy soldiers was worth inverstigating...then decided to look at countermeasures, for obvious reasons) - aerosol sprays. Tried various thing, I can't remember what, exactly, apart from powedered glass. Only drawback is deployment - anyone got a good idea for keeping a cloud of fumes surrounding the car at 80mph?
In response to the original question, I'd be surprised if it wasn't possible to pick up the scattered light from the beam. If you know the line on which the source is lasing you can pretty easily cut out all the background light with appropriate optical filters and you then look for a modulated signal on your detector. Descrimination should be fairly straightforward. Don't know if the detectors on the market do this, but it wouldn't be too difficult.
Eye safety level for visible, continuous wave, lasers is around 10mW. Look down that beam and it will
hurt and completely dazzle you. If they use near-infrared for these speed guns, then it'll probably pass through the lens of your eye and get focussed nicely onto your retina just as with visible light. (It's the focussing that provides the power density required to burn holes in the retina when you're talking about ~10mW lasers) I'd expect therefore that they'd have to keep the power output to well under 30mW to be deemed safe.
Eye safety level for visible, continuous wave, lasers is around 10mW. Look down that beam and it will
hurt and completely dazzle you. If they use near-infrared for these speed guns, then it'll probably pass through the lens of your eye and get focussed nicely onto your retina just as with visible light. (It's the focussing that provides the power density required to burn holes in the retina when you're talking about ~10mW lasers) I'd expect therefore that they'd have to keep the power output to well under 30mW to be deemed safe.Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff