Ultrasensitive spectral trace detection of individual molecular components in an atmospheric binary mixture

Ultra-sensitive all-fibre photothermal spectroscopy with large dynamic range

Photothermal interferometry is an ultra-sensitive spectroscopic means for trace chemical detection in gas- and liquid-phase materials. Previous photothermal interferometry systems used free-space optics and have limitations in efficiency of light–matter interaction, size and optical alignment, and integration into photonic circuits. Here we exploit photothermal-induced phase change in a gas-filled hollow-core photonic bandgap fibre, and demonstrate an all-fibre acetylene gas sensor with a noise equivalent concentration of 2 p.p.b. (2.3 × 10⁻⁹ cm⁻¹ in absorption coefficient) and an unprecedented dynamic range of nearly six orders of magnitude. The realization of photothermal interferometry with low-cost near infrared semiconductor lasers and fibre-based technology allows a class of optical sensors with compact size, ultra sensitivity and selectivity, applicability to harsh environment, and capability for remote and multiplexed multi-point detection and distributed sensing.

Photothermal interferometry systems using free-space optics have limits in terms of light–matter interaction efficiency, size, optical alignment and integration. Here, Jin et al. use a gas-filled hollow-core photonic bandgap fibre to demonstrate an all-fibre gas sensor with ultrahigh sensitivity and dynamic range.