Page 135 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Note: it’s a good idea to convert any spot size measurement into centimetres!!
So, if we have a laser which is generating a pulse of 1.3 Joules of energy in a 4 mm diameter spot, then:
E = 1.3 Joules
d = 4 mm = 0.4 cm
Then, the fluence = 1.3 / (0.4/2)2 which is 1.3 / 0.1256 which yields a fluence of approx. 10.35 J/cm2.
An alternative and ‘quick and easy’ way to calculate the fluence is to use ‘multiplying factors’:
      Spot diameter (mm)
    Multiplying Factor
              1
       127
    2
 32
      3
    14
     4
      8
     5
  5
     6
      3.5
     7
  2.6
     8
      2
  Now, all we need to do is take the measured energy form your laser pulse, say 1.3 J, as above, and then select the multiplying factor for the measured spot diameter – in this case a diameter of 4 mm yields ‘8’;
Then simply multiply them together: 1.3 * 8 = 10.4 J/cm2.
For a 3mm spot diameter this would be 1.3 * 14 = 18.2 J/cm2, while for a larger 8 mm spot it becomes 2.6 J/cm2.
This is more than accurate enough for most clinical applications. There’s no real point going beyond one decimal place since the measurement of both the laser energy and the spot diameter will not be that accurate!
Read more here...
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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