Three-dimensional optical path extended gourd-type photoacoustic cell for highly sensitive trace acetylene sensing.

A novel gourd-type photoacoustic cell (GTPAC) has been developed, featuring a highly reflective, polished gold film-coated inner wall that minimizes optical loss and maximizes light utilization efficiency. GTPAC integrates two coupled spherical chambers with a radius ratio 2:3, which is close to the golden ratio. Its unique Gaussian curvature distribution enables multi-directional, disordered light beam reflection without complex optical alignment. It creates a non-periodic three-dimensional (3D) optical trajectory, significantly enhancing light-molecule interactions. GTPAC achieves an exceptionally high sensitivity of up to 3.36 μV/ppm using a distributed feedback butterfly laser with central wavelength of 1532 nm (±1.5 nm) to detect acetylene gas. When the integration time is extended to 100 s, the minimum detection limit is as low as 0.59 ppb. Moreover, its flexible design and broad spectral compatibility enable significant potential for extension to other gases, such as methane and nitrogen oxides, offering new prospects for ultra-sensitive trace gas detection.