Design and testing of a modular Raman cell and air sampling system for hydrogen gas detection

Abstract

Hydrogen is emerging as a potential energy carrier and low-carbon alternative to fossil fuels. As hydrogen infrastructure grows, detecting hydrogen emissions will become increasingly important for reasons including safety monitoring, quantifying product loss, and setting greenhouse gas inventories. Laser diagnostic methods such as coherent anti-Stokes Raman spectroscopy (CARS) and photoacoustic Raman spectroscopy (PARS) can provide reliable detection of trace hydrogen gas concentrations but have primarily been demonstrated in laboratory environments. This study investigates the design of more compact system components and flow sampling hardware to enable practical field deployment of CARS or PARS for the development of a portable hydrogen gas sensing instrument. A modular Raman shifter cell was designed and tested at multiple lengths ranging from 0.5 to 2 meters. Testing involved maintaining a constant input laser energy while varying cell pressure to characterize Raman scattering conversion for a given cell configuration. In addition, a flow-through gas sampling system was designed to enable gas flow through CARS or PARS sample cells to support development of the instrument's air sampling system. Results show that reducing Raman cell length decreases the stimulated Raman scattering (SRS) conversion which can be supplemented through an increase in gas pressure within the cell. Additionally, flow-through testing with nitrogen demonstrated that flow-induced acoustic noise is a limiting factor for PARS measurements, with higher flow rates producing increased acoustic noise that can interfere with detection sensitivity. The results demonstrate that compact Raman cell configurations and controlled flow sampling systems are viable for supporting development of a portable hydrogen sensing instrument capable of active ambient air sampling in field and industrial environments.