very high collimated lens.

Hi,

I want to design a project named "high range laser distance finder". Here, my laser is not collimated and its spread. So i want highly collimated lens that can maintain laser beam to infinite range.

is it possible? or it must maintain laser beam up to 1 km.

You simple need bigger aperture. Double aperture = half divergence.
The formula is:

divergence = 2 * wavelength /(pi*aperture)

wavelength and aperture must be in same units, divergence will come out in radians.

More about beam shape here: Gaussian beam - Wikipedia, the free encyclopedia
I modified the formula because they use half of the aperture in theirs.

Based on this, with 1mm aperture and red laser you should be ideally getting 41cm spot size over 1km. With 10mm aperture it would be 4.1cm.