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Number of Ionization event estimation

Physics Asked by Bilash Krish on June 15, 2021

First of all, I am new in this field and therefore if I ask a silly question please forgive me.
I have a gas-cell (say 3$times$3$times$3 mm$^3$ volume) filled with a N$_2$ gas. The number density is known. Now I want to shine a pulsed laser light on this volume element (gas cell) with 20ns, 800nm, and energy per pulse 100 mJ. Now with a known cross-section how do I calculate the number of ionized N$_2$ per pulse?

Thanks in advance.

One Answer

For a single photon scattering/absorption event with a cross section ${sigma}$, which is $[L^2]$, or an area, the number of scattering events per pulse is:

$$ N = N_{gamma}rho_Asigma $$

Here

$$N_{gamma} = frac E {hbaromega}$$

is the number of photons in a pulse, and

$$rho_A = rho_{N_2}times L$$

is the areal density ($[L^{-2}]$) of target molecules. $ rho_{N_2}$ is the number density of molecules and $L$ is the length of the target chamber.

Correct answer by JEB on June 15, 2021

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