Two methods and apparatuses are described for hydrazine synthesis through nitrogen fixation induced by photoexcitation of N.sub.2. Both methods of photoexcitation of N.sub.2 for hydrazine synthesis involve a two-photon absorption process. The first method of N.sub.2 fixation with H.sub.2 uses a high-energy short-pulsed Nd: YAG laser with wavelength of 1.06 .mu.m. The two-photon absorption of N.sub.2 is followed by a vibrational-vibrational (V--V) energy transfer that leads to a near-complete population inversion of N.sub.2 vibrational states. The energy separation of these states is larger than the activation energy needed for N.sub.2H.sub.4 formation. The second method of N.sub.2 fixation with H.sub.2O uses a high-energy short-pulsed blue laser with wavelength of 0.4 .mu.m. The two-photon absorption at 0.4 .mu.m pumps N.sub.2 to a highly excited vibrational state, which has enough energy to both dissociate H.sub.2O into H.sub.2 and O.sub.2, and to react with H.sub.2 to form N.sub.2H.sub.4 as in the above direct method of N.sub.2 fixation with H.sub.2.