Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

Fun Spymission

F

favetelinguis

0
Joined
Jul 11, 2007
Messages
3
Points
0
Hi this is my first post on this forum hope I do i right :)

Im planing on doing some fun project with a laser since i have more free time then needed now. Im very new to the topic so please forgive me if my questions are to newbies.

First of i wonder if there are any lasers that are complitly invisible that is they dont leve any trace like red or green spots (if there are any what are thy called)?
I want to use this laser to measure movement over a distance of between 100-500meters is this possible.
How is the impact on a laser if it has to go through glass windows on its way to the target will this effect the laser and render the measurement data useless?

Where should i look to by my laser, i want the best stuff and i want to be able to hook it up to a computer.

Thanks for the help, this is some questions yest to get me started so that I know what to serarche for.

Best regards Fredrik
 





:) hi there welcome to the forums.... sounds like an interesting project uve got there.. there are lasers that are invisible to the human eye i believe. i am not sure about impacts on windows and i suppose it would depend on the measurements being gathered i suppose. as for hooking a laser up to a computer well it would depend on what you mean by hooking it up weather you need data from laser or to control it.... umm sorry this isn't very much help.... but a little more specifics would probably be required :)
 
Most humans can see all wavelengths between the UV (Ultra violet) range to the IR (Infra red) range. UV is at about 400nm and IR is at about 700-800nm. nm is a measurement, nano-meters and is equal to 1x10^-9 meters. I assume your are trying to get a laser to point at a pole or something on the far edge of where your "barrier" would be and you want to see when that barrier is crossed. Thus this is what I am going to explain. But before I do, you need to understand the danger of using there lasers. IR reflect off things that visible light doesn't and goes through things that visible light doesn't go though. A glass filled with coke would appear to be clear in front of an IR light source... mostly. IR is very dangerous to the human eye as you do not notice the damages occurring, and when you finally "see", or don't see for that matter, then you would notice the difference but it would be too late. I would personally advise that you do not have the laser going through a window if possible because this only gives you erroneous stray reflections and loss of power and also tends to refract the laser and ruin the beam properties.

With that said... here's a very easy thing you can do. What you need is a collimated IR laser, about 1-5mW power should be more than enough. Point your laser at a pole or tree at one edge and place a webcam at that target. Using a software that senses motion in the camera, you can have your computer beep and whistle and create pop-ups and start jumping up and down if you want. The point is to have the webcam's IR filter removed. Point the webcam on the laser target ONLY. Turn up the sensitivity on the software to as much as possible and then have it conditioned for what you want it to do in case of an intrusion. When the laser is interrupted by anything from a small mosquito to a huge bear, if the dot moves, you sense motion! :D

This is a very simple application of what many 'laser fences' do. The commercial applications use photodiodes or photosensors that are activated in case the laser is interrupted. With photodiodes the target is the photodiode itself and if it doesn't see a laser then obviously the laser is interrupted. In the case of a photosensor, then the system works effectively as I described with a webcam, but on a more discrete and commercially applicable level. You can experiment and try to get things right, if you have any knowledge of software and how to make a program that senses motion in a camera, then you've got it made. Otherwise I advise you ask around or buy one. I can write one, but it would take me a while and I am not motivated honestly...

Also... obviously you need to power the laser diode... for that, in itself, is a huge ordeal. A battery won't live as long as you need it, and a power source would have to be very filtered and regulated. That I assume is a separate stage that we can discuss later if you decide to see this project any further. :)

Good luck;
DDL
 
Hmm interesting example but not what i want to do. I would like to use my laser to messuer speed on objects that are about 100-200meters away from me.
I would like to point my laser at a specific point and when something flyes by it i would like for it to repost the speed of the object back to my computer. I would like the laser to be invisible to the human eye and the laser is probably going through at lease 1window glass.

Do this sound possible at all? Thanks for the help.
 
You sound like you are re-inventing the wheel on the cheap ! Police use a system like that to catch speeders....perhaps a tiny bit of research into how those "guns" work would be a good idea ??
 
HAHAHAHAHAHA... you want a laser speed detector? :o Ya... forget it. The kind that cops use uses modulation and calculates modulation differences while using a very sophisticated filtering system... trust me, it's not something you wanna get into. I'm not sure about 'laser' guns per say... but I'm sure they follow the same concept by measuring the pulse-return time or something like that and then calculating the differences.

Either way... good luck with that and keep us posted :)

--DDL
 
You know, I don't know much about using lasers for that purpose, but Hot Wheels sells a microwave radar gun that actually has about 120m range IIRC... Some guys over at rougesci were using it to try and clock the velocities of their detonations or some such! ;D

Edit: Wow, 2 posts while I typed that out. IIRC Police radar guns use microwaves, dont they?
 
Hmm maby im overlooking something but what is so advance about shooting a laser 2 times at the same object and compare the return time to get the speed of that object?
 
Well, you would have to ensure that the surface you aim at would give a precise reflection straight back at you - you would have to have the speed of light programmed into your computations, etc...it's not that it cannot be done - it is just a lot more involved, and with existing technology in place - hence my comment about reinventing the wheel....
 
This is easy to do with sonar because the speed of sound is slow (comparatively) and the doppler effect more pronounced and easy to measure. With light, you're dealing with something that has a fixed speed (to any observer within a particular frame of reference, blah, blah, Einstein, etc.) and that fixed speed is the absolute fastest that anything in the Universe can move at. In addition, the amount of time that it takes for a light pulse to reach you is rediculously small, and the doppler variation between pulses smaller still. If you can make this work on a DIY device, then all the power to you but it is not an easy task!
 
I won't tell you it can't be done... it can be done... but the device that analyzes and detects such signals is not as simple as one that does the same for radio waves... :(

--DDL
 
Justin said:
With light, you're dealing with something that has a fixed speed (to any observer within a particular frame of reference, blah, blah, Einstein, etc.) and that fixed speed is the absolute fastest that anything in the Universe can move at.
Click to expand...
being both pedantic and a science geek, i must point out that the fastest anything can travel is the speed of light in a *vacuum*, and light in any other medium (such as air, water, etc) is slowed down a tiny bit...scientists have even used special materials to slow light down to 17 meters per second! but still, light in air is travelling almost the speed as in a vacuum, so it would still be very difficult...also, glass slows down light even more, to about two thirds speed, so i'd guess shining through a window would mess up or at least complicate calculations...
 
actually, if you google around, you should be able to find laser range finders... i'm not sure how helpful these will be, and they're not cheap (seem to be $300+) but if you could hook up the readout of one to a computer and measure the difference between laser-measured difference in a set time...?
 
Marianne: Good point about the medium, but as long as you are within the medium then the speed of light within that medium will then be the speed limit for everything... light, information, etc. If you were in water, then the speed of light within the water would be the speed limit for any sort of interaction or communication unless you're measuring gravitational waves, which may or may not be transmitted by particles depending on who you believe. (I know that the "graviton" is commonly accepted as the solution to that question, but no one has found one yet so it's just a pretty-sounding theory at this point!)
 
Considering this new point about gravity I couldn't help but wonder if it actually worked... With the speed of light actually slowed down enough in the right medium, would we ever see light... falling? Or being pulled towards the center of gravity due to the new lower speed? LOL That would be quite a sight... a curved laser... I call it 'Curved LASER'.

:)
DDL
 
You must log in or register to reply here.





Back
Top