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You are watching: How many photons are in the laser pulse?


Have you ever before wondered how numerous photons you generate each time girlfriend fire a pulse that laser energy? i have!

Fortunately, I can work the out since I’m a physicist. It’s the kind of point us physicists do!! the keeps us off the roadways at night……

So, to calculate this number we require to understand the power of every individual photon. This is rather easy to carry out using a formula native quantum physics:

E = h f

where ‘E’ is the photon energy, ‘h’ is Planck’s continuous and ‘f’ is the frequency that the light. Max Planck to be a an extremely clever physicist who helped to develop quantum physics ago in the early on 1900s. Making use of the above simple formula we have the right to calculate the energy of a photon of any kind of wavelength (remember, wavelength = the rate of light / frequency).

So, listed below I display the power of photons that a variety of wavelengths frequently used in skin science lasers:

 Wavelength (nm) Photon energy (joules)
 532 – Nd:YAG, second harmonic3.734 x 10^-19
 585 – pulsed dye laser3.396 x 10^-19
 694 – ruby laser2.862 x 10^-19
 755 – alex laser2.631 x 10^-19
 1064 – Nd:YAG1.867 x 10^-19

Notice the the separation, personal, instance photon energy falls as they become ‘redder’!

Now, we simply divide the number of photons (above) into the pulse power used in a treatment. Let’s say the the pulse energy is 1 joule; so the variety of photons for each wavelength is:

 Wavelength (nm) Number the photons
 532 2.6781 x 10^18
 5852.9449 x 10^18
 6943.4936 x 10^18
 755 3.8007 x 10^18
 10645.3562 x 10^18

That’s a lot of photons!!!

To placed that into some sort of perspective, let’s compare these numbers against something an ext tangible.

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How numerous grains that sand are there ~ above the world Earth? Well, follow to The math Dude there are approximately 5.6 x 10^21 grains!!!

That’s 5,600,000,000,000,000,000,000!

So, by this reckoning, when you fire off 1000 pulses the 1064nm laser energy at 1J every pulse, girlfriend will have actually generated around the same number of photons together the total variety of grains that sand top top the whole planet!

If your laser runs at 10 Hz (10 shots per second) climate you only need 100 seconds, or much less than 2 minutes, that shots to same all that sand.