Solve Math Simulation for Laser Microphones

  • Thread starter Ghassan99
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In summary, the device emits a laser beam and flexes a window to redirect the beam. The vibrations in the glass cause a slight change in the focal length of the beam, which in turn changes the voltage across the photo detector. This causes the audio to fluctuate.
  • #1
Ghassan99
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I have been trying to write the mathematical simulation for this device but unfortunately I found no clue to start with .
the simulation should be starting with the Gaussian beam equation of the laser source and then the vibrations in the glass pane cause the window to flex, changing the center of curvature of the window, thereby causing the "focal length(=measure of how strongly the system(glass) converges or diverges light) of the window to change, albeit very slightly. This creates a varying divergence and converges in the reflected laser beam which then can be directed to a photo diode causes the voltage across the detector to fluctuate.
I'm really desperate for a mathematical simulation for this process.
 
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  • #2
Ghassan99 said:
I have been trying to write the mathematical simulation for this device but unfortunately I found no clue to start with .
the simulation should be starting with the Gaussian beam equation of the laser source and then the vibrations in the glass pane cause the window to flex, changing the center of curvature of the window, thereby causing the "focal length(=measure of how strongly the system(glass) converges or diverges light) of the window to change, albeit very slightly. This creates a varying divergence and converges in the reflected laser beam which then can be directed to a photo diode causes the voltage across the detector to fluctuate.
I'm really desperate for a mathematical simulation for this process.

That's not how a laser microphone works. What makes you think it is a modulation in a focal length?
 
  • #3
that's what I have studied , do you have any other idea i assume?
 
  • #4
the usual way is that the laser is reflected off the window back to a receiver
The flexing glass FM modulates the laser signal which is then demodulated and the audio recovered

Dave
 
  • #5
I guess it is possible to build a system based on an optical lensing receiver system with an extremely shallow depth of field such that microscopic defocusing would cause the field to increase enough that the amount of light on a critically sized sensor would vary enough to be detected.

But, I think the more common approach is an interferometer based approach where the reflected signal's phase varies due to the path length changes and is summed with a reference from the transmitter. This produces an AM light signal.
 
  • #6
hi mebigguy

it may well be AM ... Berkeman PM'ed me with same thoughts
my reasoning for it being FM was that there was a Doppler effect in action which would produce an FM'ing of the laser beam

I don't understand how the laser is AM modulated by a sheet of glass vibrating back and forward ?

cheers
Dave
 
  • #7
It is an interferometer. The distance to the reflector and back changes as the reflector vibrates. This causes a phase change which is detected by summing with a portion of the transmitted signal.

http://www.williamson-labs.com/laser-mic.htm explains different approaches, including one that is not an interferometer.
 
  • #8
davenn said:
the usual way is that the laser is reflected off the window back to a receiver
The flexing glass FM modulates the laser signal which is then demodulated and the audio recovered

Dave
mathematically please
 
  • #9
meBigGuy said:
It is an interferometer. The distance to the reflector and back changes as the reflector vibrates. This causes a phase change which is detected by summing with a portion of the transmitted signal.

http://www.williamson-labs.com/laser-mic.htm explains different approaches, including one that is not an interferometer.

interesting link, saved that one :)

fig 3 is the way I was thinking, but that isn't listed as the interferometer as the others are
So is that one PM, AM or FM or a mixture ?

Dave
 
  • #10
Figure three is just detecting angular deflection of the window the same as figure 2.

It has to work such that the laser light boundary falls through the middle of the detector, and the deflections change the area exposed to the laser. (half the detector is lit with no deflection, all or none with full deflection)

So in principle there is no "modulation" of the light in that application. It is just that the beam is moved off the detector.

BTW, doppler shift of light is not detectible by a photodetector. FM modulation is constant amplitude.
The interferometer actually AM modulates the light intensity. The detector tracks the intensity.
 

FAQ: Solve Math Simulation for Laser Microphones

1. How does a laser microphone work?

A laser microphone works by using a laser beam to detect vibrations on a surface. The laser beam is directed at a surface, and as sound waves hit the surface, they cause tiny vibrations that can be picked up by the laser. These vibrations are then converted into electrical signals, which can be amplified and turned into audible sound.

2. What is the purpose of using a laser microphone in a math simulation?

The purpose of using a laser microphone in a math simulation is to demonstrate the principles of sound wave detection and conversion into electrical signals. By using a laser microphone, students can see how sound waves can be converted into measurable data and learn about the mathematical formulas and calculations involved in this process.

3. Can a laser microphone be used for eavesdropping?

Yes, a laser microphone can be used for eavesdropping. However, it is not a commonly used method for eavesdropping as it requires precise positioning and high-quality equipment. Additionally, the sound quality may not be as clear as with other eavesdropping methods.

4. What are the limitations of using a laser microphone in a math simulation?

One limitation of using a laser microphone in a math simulation is that it may not accurately reflect real-life conditions. In a simulation, the laser beam is directed at a flat surface, but in real-life situations, the laser may need to be adjusted to account for different surfaces, angles, and distances. Additionally, environmental factors such as wind and ambient noise may affect the accuracy of the results.

5. What are some real-world applications of laser microphones?

Laser microphones have several real-world applications, including military and law enforcement surveillance, industrial monitoring, and acoustic research. They can also be used in non-destructive testing to detect defects in materials and structures. Additionally, laser microphones have been used in the entertainment industry for recording and amplifying acoustic instruments.

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