Abstract: A gallium nitride group compound semiconductor laser diode (10) satisfying the formula (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N, inclusive of 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1 comprises by a double hetero-junction structure sandwiching an active layer (5) between layers (4, 6) having wider band gaps than the active layer (5). The active layer (5) may comprise magnesium (Mg) doped p-type conductive gallium nitride group compound semiconductor satisfying the formula (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N, inclusive of 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1 . In another embodiment, the active layer (5) is doped with silicon (Si).

Abstract: An organic nonlinear optical material comprising a 4-nitrophenylaminoacetaldehyde acetal of the following formula (I): ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 each represent a hydrogen atom, or a linear or branched alkyl group having 1 to 6 carbon atoms, and R.sub.4 represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a nitro group or a halogen atom.