Calculated electronic energy level of nitrogen molecule. HOMO indicates the higher occupied molecular orbital, and LUMO indicates the lowest unoccupied molecular orbital. The photon energies corresponding to 800 nm and 1600 nm lasers are 1.56 and 0.78 eV, respectively. The vibration energy of nitrogen is about 0.2 eV. The energy gap that matches the energy of 1600 nm photon is colored blue, and the possible transitions between the gap are depicted on the right.