Polarization of Laser vs Sunlight

[nepstein]

Hi all,

I'm implementing a computer vision system with a near-infrared laser and a NIR bandpass filter. It shines a laser on things and looks for a reflection. I'm getting a bunch of interference from sunlight and was thinking of using a polarizing filter to cut some of the sunlight out.

Anyone know if laser light is polarized to begin with, and in which direction? Most of the sunlight interference isn't direct, but reflection off a concrete floor. Anyone have experience with this? Other ways to cut out sunlight from laser light other than polarization?

I'm open to all suggestions! Thanks so much.

 

[UltrafastPED]

Most lasers are polarized due to the design of the cavity/cut of the crystal. You can check the specifications for your laser. If Brewster's angle is used, it will be plane polarized as it exits, but it is easy to change via the correct wave plate - the angle can be rotated, or it can be converted to circular polarization. You can also verify the wavelength & bandwidth of the laser ... you may just need a better notch filter.

Wave plates: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/quarwv.html#c1

Polarization concepts: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polarcon.html#c1
This is a good learning site!

Sunlight is not polarized, though the atmosphere does generate some partial polarization, which changes during the day - professional photographers have to allow for this when they choose filters:
http://www.polarization.com/sky/sky.html
http://www.cambridgeincolour.com/tutorials/polarizing-filters.htm

Also see http://en.wikipedia.org/wiki/Rayleigh_sky_model