Laser absorption spectroscopy of oxygen confined in highly porous hollow sphere xerogel

Fabrication and characterization of porous tissue-mimicking optical phantoms as a tool for optical sensor validation

This paper presents porous polydimethylsiloxane (PDMS) optical phantoms with tunable microstructural and optical properties to mimic porous biological tissues (e.g., fruit) during the design and optimization of novel optical setups. A well connected salt network formed using salt particles of various size distributions was used to obtain porous PDMS phantoms of different porous features including porosity, pore size distribution, pore number density and pore connectivity. These microstructural features are strongly related to the light scattering from the phantom where a higher reduced scattering coefficient ( μ s ' ) was observed from the porous PDMS phantom with a higher number of small pores compared to the optical phantom with a lower number of larger pores. The prepared phantoms were used to validate GASMAS (gas in scattering media absorption spectroscopy) H₂ O and O₂ sensors by quantifying the optical path length through the pores and the O₂ concentration inside the pores.

Methane detection using scattering material as the gas cell

A compact methane (CH₄) detection system is presented and developed by using an alumina ceramic scattering material as its gas cell. Due to the material's high scattering performance, the optical path length of the gas cell at 1653.7 nm can reach 15.96 cm although its physical length along the light transmission direction is only 0.50 cm. The wavelength modulation spectroscopy technique is employed to enhance the detection sensitivity, and the second harmonic gas absorption signal with low noise is detected and processed. The long-term stability of the system is investigated by the Allan deviation analysis method. Detection limits of 4.5 and 2.6 ppm are achieved at averaging times of 20 s and 200 s, respectively. The dynamic gas exchange performance is also experimentally studied. The experimental results indicate that our system is a good choice for practical applications owing to its small volume, high sensitivity, and stability.