What is $[\mathrm{J}]$ supposed to denote in this case?

Question

I am currently studying Laser Systems Engineering by Keith Kasunic. Chapter 1.2 Laser Engineering says the following:

If the energy of the incident electromagnetic field more-or-less matches that of the electron’s excited state energy $E_2$ compared with some lower-energy state $E_1$, then there is a high probability the electron will give up its energy in the form of a stimulated photon whose energy $E_p$ in Fig. 1.9(a) is $$E_p = E_2 - E_1 = h \nu = \dfrac{h c}{\lambda} \ \ \ \ \ \ \ [\mathrm{J}] \tag{1.2}$$ where $h = 6.626 \times 10^{-34}$ J-sec is Planck’s constant.

What is $[\mathrm{J}]$ supposed to denote in this case? I read this relevant question on square brackets in dimensional analysis, but I don't think it clarifies what it means in this particular case.

Answer 1

$$E_p = E_2 - E_1 = h \nu = \dfrac{h c}{\lambda} \ \ \ \ \ \ \ [\mathrm{J}] \tag{1.2}$$ where $h = 6.626 \times 10^{-34}$ J-sec is Planck’s constant.

Another way of writing this is,

$$E_p/J = E_2 - E_1 = h \nu = \dfrac{h c}{\lambda} \ \ \ \ \ \ \ \tag{1.3}.$$

It means that $E_p$ is expressed in units of $Joules$, so $E_p/J$ is $E_p$ per unit $J$.