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This paper presents an optimized T-type resonant photoacoustic (PA) cell for methane (CH 4 ) gas detection. The noise transmission coefficients and PA field distributions of the T-type resonant PA cell have been evaluated using the finite element method and thermoviscous acoustic theory. The optimized T-type resonant PA cell, together with a near-infrared (NIR) distributed feedback (DFB) laser source, a high-speed spectrometer and a fiber-optic acoustic sensor constitutes a PAS system for CH 4 detection. The sensitivity is measured to be 1.8 pm/ppm and a minimum detectable limit (MDL) of 9 parts per billion (ppb) can be achieved with an averaging time of 500 s. The optimized T-type longitudinal resonant PA cell features of high PA cell constant, fast response time and simple manufacturing process.

The construction of functional photonic structures in transparent solids for various applications, such as 3D displays, optical information processing, and tunable lasers, is of great scientific and technological importance. Here, self-assembled crystallite-based grating nanostructures are created in an unconventional multicomponent glass with an ultrafast laser. The novel nanogratings are organized as periodically assembled crystalline and amorphous phases, exhibiting strong polarization-dependent birefringence. The Ta 2 O 5 component in the glass strongly contributes to the creation of nanogratings. Furthermore, a picosecond laser rather than a femtosecond laser is established to more suitably create nanogratings in the target glass, proving the critical role of thermal accumulation during nanoscale crystallization. Finally, nanogratings are demonstrated to be broadband variable near-infrared optical attenuators with a high attenuation ratio,

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