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Explanation of laser intensity

  1. Dec 10, 2009 #1
    I've become interested in lasers and this question came to me today. Let's say we have two 10 mW lasers. One has a spot size of 1mm and one has a spot size of 10mm. Therefore, the first laser has a greater intensity. In classical physics we are told the wave amplitude increases. In modern physics we have more photons. Do either of these concepts relate to spot size (cross sectional area of a laser beam)? Also, what determines the spot size of a laser from a functional point of view? - Thanks
     
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  3. Dec 10, 2009 #2

    Andy Resnick

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    Since the lasers have equal power output, increasing the beam diameter decreases the intensity (units [W/m^2]). Note that in photometry, the quantity of [W/m^2] is *irradiance* (or emittance, or exitance) while 'intensity' is [W/sr].

    Laser beams are often approximated as "Gaussian beams", and so the minimum spot size is inversely proportional to the beam spread angle (divergence). I'm not sure what sets the beam diameter at the laser aperture, but it may be related to the resonator geometry and manufacturing constraints.
     
  4. Dec 11, 2009 #3
    Yes, I realize this. Let me clarify as my title was misleading. I interpret light as a particle traveling in the x-direction yet oscillating in the y-direction. The "particle" hits within an area of known probability. Do this thousands of times and you have a dot, right? I was wondering if this had anything to do with spot size.
     
  5. Dec 11, 2009 #4

    Andy Resnick

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    Sure- that's how diffraction is analyzed in terms of particles.
     
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