High resolution spectroscopy of ammonia in a hollow-core fiber.

We have demonstrated frequency modulation saturation spectroscopy of the nu(1) +nu(3) band of ammonia in hollow-core photonic bandgap fibers (HC-PBFs). Previously blended lines have been resolved and the corresponding molecular transitions assigned. Cross-over resonances are observed between transitions that do not share a common level. We have measured the pressure dependence of the line shape and determined the collisional self-broadening coefficients for ammonia. The many absorption lines of ammonia in the 1.5 microm wavelength region are potential frequency references lines for optical communication as well as candidates for spectroscopic trace gas monitoring.