Detection of nuclear spin isomers of water molecules using self-scanning Tm-doped fiber laser

A near infrared spectrometer based on the self-scanning Tm-doped fiber laser is developed. The spectrometer is applied to measurements of the water nuclear spin isomer abundances using water absorption lines in the vibrational band near 1.91 µm. The ortho/para ratio of water nuclear spin isomers is measured to be equal to 3.06 ± 0.02, which is close to the theoretical prediction of 3 at room temperature.