#### jayjay23

Joined Sep 30, 2011
12
can someone help me with my research on different type of laser and their min/max ranges. specially a laser that can track a photo-diode at a long range. e.g 50ft and above.

Thanks as you help

#### thatoneguy

Joined Feb 19, 2009
6,359
Most any laser diode will go 50ft.

What level of accuracy are you looking for, and what sort of feedback system for tracking?

#### jayjay23

Joined Sep 30, 2011
12
basically i need to point the laser beam toward a set of sensor to keep a vehicle on a straight line, i have 2 ways of operation.
1. The laser will be pointed toward a sensor(photo-diode) and as long as the sensor can sense the presence of the leaser beam the vehicle will be kept on a straight line.
2. There will be 2 sensors mounted on a vehicle and leaser beam pointed in the middle. as long as the sensors do not sense the laser beam the two back wheels of the vehicle will be at same voltage, when one of the sensors sense the presence of the laser beam e.g. the left sensor send the beam, the voltage in the left wheel will decrease and which will make the vehicle to make a slight left turn.

i need to track the sensor from a long range between 50ft to 200ft
i like the second idea better, i hope that give more light to the question

#### THE_RB

Joined Feb 11, 2008
5,438
A 5W red laser diode with lens is safe enough and commonly available and will make a good bright spot 50ft to 200ft, although the spot will get larger at 200ft of course.

Why not buy a $10 red laser pointer from ebay and do some initial tests? #### thatoneguy Joined Feb 19, 2009 6,359 Your idea sounds workable if you have a smooth floor. I agree with your idea of using two, possibly more, such as one non-laser, but LED through decent Fresnel lens so the rough direction could be found, and the laser guidance could take over from there. #### gerty Joined Aug 30, 2007 1,298 A 5W red laser diode with lens is safe enough and commonly available and will make a good bright spot 50ft to 200ft, although the spot will get larger at 200ft of course. Why not buy a$10 red laser pointer from ebay and do some initial tests?
Wouldn't that be 5 mW instead of 5W? Or are we talking about totally different things

Joined Dec 26, 2010
2,148
5W? Do I smell fried photodiode?

You will see many laser pointers sold as "5W", but mercifully their true output powers are much lower. A real 5W laser is a dangerous piece of hardware which can do irreparable eye damage in an instant.

A collimated beam that strong would probably go for miles on a clear day, but would surely be be far too dangerous for this purpose, as well as very costly.

I doubt that a student would want to use anything over a few mW for this sort of' experiment, especially if it is an open area.

Most likely if this is a college project there will be fairly strict rules about what is allowed. http://en.wikipedia.org/wiki/Laser_safety

#### jayjay23

Joined Sep 30, 2011
12
thanks guys for the contributions, it goes in more details but i don't want to bored you guys with it. i have a laser pen which i bought on ebay some times ago i guess i will do some experiment to see how far it can reach. just one more thing do anyone no of a website that have different types of laser i could use for this experiment and there specification?.

#### thatoneguy

Joined Feb 19, 2009
6,359
www.wickedlasers.com

Over priced, but decent stuff tht matches specs, also covers safety when working with lasers.

Your application should be in the 5-10mW range tops.

#### jayjay23

Joined Sep 30, 2011
12
quick question, sorry so much question im just finding my way round this laser project. what the difference between a single mode laser and a multimode, and also what is the difference between a 375nm and a 473 wavelenght

#### thatoneguy

Joined Feb 19, 2009
6,359
quick question, sorry so much question im just finding my way round this laser project. what the difference between a single mode laser and a multimode, and also what is the difference between a 375nm and a 473 wavelenght
373nm and 473nm wavelengths are 100nm apart.
UVA 320-400 nm
Blue - 475 nm

There aren't single mode and multi-mode lasers. You must be thinking of fiber optic.

Single mode fiber has a very, very thin core an will only carry one ray of light at a time.

Multi-mode fiber has a larger core, and can carry multiple rays and frequencies of light at the same time, see Wikipedia on Multi-mode fiber

The difference between lasers and other light sources is their output is coherent, e.g. all polarized in the same direction, so dispersion and spread is very low, and focusing can be "perfect", so collimation to a single beam is simple.

#### THE_RB

Joined Feb 11, 2008
5,438
That was indeed supposed to be 5mW.

I'm not sure what failed; brain/finger/keyboard but the 'm' went missing for sure.

#### davebee

Joined Oct 22, 2008
540
Cheaper semiconductor lasers emit light at multiple wavelength peaks that are fairly close together; they are called multimode lasers.

They are fine for many purposes, but for the highest speed optical fiber communication, they aren't so good, so the better lasers are tweaked to emit their light mostly at a single peak - those are called singlemode lasers.