Laser Microphone

[tx00824]

Hi guys, I am thinking about building a laser microphone and found quite a bit of sites and videos on google about it but most of them are the angular solutions there is also this bounce back solution with beam splitter look here Fig 3.

I have a question about the beam bouncing, on the diagram laser is shown to be perpendicular to the window plane (in reality then it would have to be aligned along the normal vector of the plane of window) which makes sense, but it seems impossible to achieve in the reality.

I have looked into laser measures and seeing how they work on similar principle of bouncing the beam back and measuring time it travels in this case. I noticed on the videos that measurement can be taken at any angle, so it made me thinking that some of the light gets bounced back at the angle of 0 degrees same way it came from, Is this correct??

Sorry if my question seems very newbie but I have very little idea about lasers at this point.

 

[qumefox]

Laser rangefinders work by sending out pulses of laser power and they measure the time it takes those pulses to return, It doesn't take a lot of photons returning to get enough data to determine the range and most objects will reflect enough to do the job regardless of angle. It's pretty much sonar, except using light instead of sound.

With your laser mic application, you need a CW laser signal, not just pulses, and to get that, you need a clear constant reflection path.

 

[tx00824]

qumefox, so then this type of microphone described on FIG 3 is only going to work as I suspected when directly perpendicular to the plane of glass, but this seems impossible to achieve in real life, to find the angle while being far away from the window will be extremely difficult. Anyway this experiment will not cost me much so I will have a go anyway

I have another question, about Beam Splitter, where can I get one cheap. I think that CD, DVD and BR players have one inside, is this true? so I just buy one and extract it.

I have ordered for my experiment blue laser pointer 405nm, 1mW power, I know that there are different Beam Splitters for different wave lengths (blue, red, green) so which one should I choose for my experiment would it be the Blue Ray splitter? Or maybe I should just buy red pointer and CD splitter it seems cheaper.