Creating a Paralell Beam from Line Laser

Hi There, I need to create a non diverging, Red laser Beam for a gesture detection experiment. I have a Line laser which creates a line ideal for the purpose, but the line created is projected with a beam angle of around 50 degrees. (i.e. the length of the line varies according to the distance of the projection surface .)
I am looking at placing a Optical Lense / Grating which will create a paralell beam such that the created laser line does not grow with the distance. Any ideas on what / where I can find the intermediary device needed for my activity. Any assistance/advise is much appreciated.
Genny

You'd need a cylindrical lens or mirror, but it's hard to find big ones.

How wide of a line do you need? You will need a lens of that size to stop the spread at that width.
Types of simple lenses
Perhaps you could make do with just a line that spreads less? Like 38° AixiZ Line Generators

I think he wants a line that is the same length at all distances ie no "degree" value. Mr. blue's idea certainly would work.

Here's something I just tried that works okay: laser focused into a line generator lens (focal point in or near the line lens) followed by a large Fresnel lens (page magnifier, for example - available for a few dollars) at one focal length away from the line generator optic. It's certainly not the best quality, but it is probably the cheapest solution and might be good enough.

Dear All, Thank you very much for your kind replies and advise. Actually my ultimate experiment uses IR Lasers (5mW at the moment, using 780nm and 980nm but for Calibration purposes I use a Red Laser. All lasers are Line Lasers. I desire the beam width (not height) to be around 25 cm. laser line beam height is fine as it is.

I did use a Fresnel Lens (off a Old Overhead Projector), and pointed the beam (line) at the centre. it did create a line, but it was projecting at an angle. Actually as the attached image (TOP View) would indicate, I am trying to measure the length of a object using a camera, and when the line laser projects as it is the shadow created by the object varies according to the location (i.e. as in the picture, I would find the length of object 1 to be longer than object 2, while ideally i must get the same value)...Thank you very much.

genny said:

...it did create a line, but it was projecting at an angle.

Click to expand...

What do you mean by that?

i,e the shadow length of the objects placed varied, as in the original situation, and the laser line (if viewed from top) was still perhaps projecting at an angle (v shape).

Of course, I did not place the line laser at the f length as you mentioned.
How can I find out the f length of the OHP Fresnel Lens ?

Thanks once again!

It would be easier to just move it forward or backward until you get what you want. If it is too far away, the line will converge. If it is too close, the line will diverge. One google result puts the FL at around 132mm which means with a 50 degree line lens you'll only get a 115mm line. Another result placed it at 280mm which means a 240mm line so it depends on the model.

What about using two different color lasers, spaced a known distance apart, using the same line generating optics throwing out at the same angle? You'll have to do some trigonometry and subtraction instead of directly measuring a shadow...

Thanks all for the comments and advice. I will try to test using fresnel lense. for the two beam option, i have to use two IR wavelengths - perhaps 780 and 980 nm, and use two filters and two cameras, as the experiment uses IR and not visible light.

I just tried the Fresnel idea and it works...
just move the Line laser closer or farther away from
the lens until the line on the lens it as big as the line
on a wall..

The only thing I see as a problem is that if you want
your parallel beam 3 feet wide... you will need a 3 foot
Fresnel lens surface...


Jerry

I still havent been able to get a perfect line. but will try further. Using a 5mW Red Laser, and OHP Fresnel (Does it have a side ?). The line i need is around 25 cms, within the range of the width of the fresnel lense