Nonlinear optical generation in a hydrogen discharge

Sum-frequency generation with electromagnetically induced transparency (EIT ) has been examined in a hydrogen discharge. EIT is demonstrated in the 3p- 1s and 4p-1s transitions at 102.6 and 97.3 nln, respectively, with increase d efficiency of generation arising from higher H-atom density, although com peting effects due to the presence of Hz distort the line shapes of these s pectra. Only for shorter-wavelength transitions (such as 7p-1s and 8p-1s) t hat show very large shifts and distortions is there a decrease in intensity in comparison with generated radiation from H atoms external to the discha rge. [S1050-2917(99)01404-3].