Microwave optical double resonance spectroscopy of ammonia in a hollow-core fiber.

We have demonstrated microwave optical double resonance spectroscopy of the nu(1) + nu(3) and nu(1) + 2nu(4) bands of ammonia in a hollow-core photonic bandgap fiber. Signal strength and lineshapes are analyzed. Spectroscopic assignments of previously assigned lines and previously proposed assignments have been confirmed and new assignments have been made. Several microwave transitions in the excited vibrational states have been measured for the first time.