Parameters

W_Fin : waist radius of the incident beam at the fundamental wavelength
W_Fppln : waist radius of the beam at the fundamental wavelength in the PPLN
λ : fundamental wavelength
length_ppln : PPLN length
thick_ppln : PPLN thickness
temp_ppln : PPLN temperature
W_SHout : waist radius of the output beam at the second harmonic wavelength
f₁ : focal length of the lens L1 focusing the beam at the fundamental wavelength in the middle of the PPLN
dist_{WFin_L1} : distance from the waist of the incident beam at the fundamental wavelength to lens L1 (the system is configured so that the waist is in the front focal plane of L1)
dist_{L1_ppln} : distance from lens L1 to the PPLN entrance
W_SHppln : waist radius of the second harmonic beam in the PPLN
f₂ : focal length of the lens L2 collimating the beam at the second harmonic wavelength
dist_{ppln_L2} : distance from PPLN exit to lens L2
dist_{L2_WSHout} : distance from lens L2 to the waist of the collimated beam at the second harmonic wavelength (the system is configured so that the waist is in the back focal plane of L2)