 Solution

For the harmonic-oscillator recoil matrix element, using ${\psi }_1=\sqrt{2}(x/l_0){\psi }_0$ and differentiating the Gaussian transform with respect to $k$,Consequently $|M_{01}{|}^2/|M_{00}{|}^2={\eta }^2$. Reversing the travelling-wave phase changes the sign of the imaginary amplitude. For small $\eta$, the sideband is weaker by $\eta$ in amplitude and ${\eta }^2$ in probability.

With the printed unnormalized Gaussians, the literal integral would be $-2igk{l}_0\exp (-k^2{l}_0^2/2)$. It is distinguished from the physical normalized-oscillator result rather than silently treating inconsistent wavefunctions as normalized.