I am not sure this is the right place where I should post, I hope I've chosen the right section.(adsbygoogle = window.adsbygoogle || []).push({});

I'm studying laser's fundamentals on Svelto's "Principles of Lasers". Here I find the description of a generic four level laser by means of rate equations; it can be represented like this: (first picture)

Then, I read that the CO2 laser, whose basic scheme is in the second picture, can be modeled as a four-levele laser too; I don't understand why this is true. In the CO2 laser the radiative transition is between level 3 and 2, while in the first photo it is between 2 and 1. Moreover, level n.3 in the first picture should be pratically empty, while in the CO2 laser it isn't so.

Can anyone explain me how I can model a CO2 laser like a four-level laser like the one in the first picture?

Thanks.

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# Four Level Laser

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