Measurements of NH(3) absorption coefficients with a C(13)O(2)(16) laser

Area of Science:

• Spectroscopy
• Laser Physics
• Environmental Monitoring

Background:

• Ammonia (NH3) detection is crucial for environmental monitoring.
• Carbon dioxide (CO2) lasers are used for gas sensing.
• Accurate absorption measurements are needed for efficient detection.

Purpose of the Study:

• To measure NH3 absorption coefficients for specific C(13)O(2)(16) laser transitions.
• To investigate the pressure dependence of NH3 absorption.
• To determine the frequency separation between laser and absorption lines for improved detection.

Main Methods:

• Absorption spectroscopy using a C(13)O(2)(16) laser.
• Measurements conducted at low NH3 concentrations broadened to 1 atm with N2.
• Determination of absorption coefficients (K) for R(8) to R(28) transitions.

Main Results:

• The strongest absorption coefficient (K = 36.09 ± 1.43 (atm-cm)−1) was found for the R(18) transition, exceeding previous CO2 laser measurements.
• Frequency separation between the R(18) laser and aQ(6,6) NH3 line determined as 550 ± 50 MHz.
• Pressure dependence of K was analyzed for selected transitions.

Conclusions:

• Enhanced NH3 absorption coefficients facilitate a ~40% reduction in path length for long-path monitoring.
• The determined frequency separation is suitable for heterodyne detection using Hg-Cd-Te photomixers (bandwidth ≥ 1.5 GHz).
• These findings advance the capabilities of CO2 laser-based ammonia sensing technologies.