# Design and construction of a system identifying molecular nitrogen and water

I have read papers that use LIDAR-like and LIDAR-Raman systems that detect elements.

I want to measure the vapor water ($$\rm H_2O$$) and $$\rm N_2$$ of trees/agriculture using Arduino and low cost elements (DIY).

I am thinking of using 405 nm, 50 mW laser. The problem is how can I detect the returned wavelength?

What I am thinking:

1. A CCD sensor?
2. A Photodiode array?
3. A modified webcam?
4. A photodiode with a filter?

My question is what do I measure with the wavelength sensor? The time from when I send the pulse of the laser and the time it returns in the wavelength sensor? Only the wavelength? Should I send a specific coded message with the laser? For example 101010011?

• I’m thinking you first need a laser safety officer to discuss shining a 3b/borderline 4 laser around outdoors. Also note that you need some really good optics folks to make LIDAR, much less LIDAR/Raman work. – Jon Custer Sep 25 at 20:23
• Yes, You are right, I meant 50 mW. My fault! – just_learning Sep 25 at 20:50