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

Area of Science:

• Spectroscopy
• Optical sensing
• Chemical detection

Background:

• Photothermal interferometry offers ultra-sensitive trace chemical detection.
• Previous free-space optics systems had limitations in efficiency, size, and integration.
• A need exists for more compact and efficient photothermal sensing technologies.

Purpose of the Study:

• To develop an all-fibre acetylene gas sensor.
• To overcome limitations of free-space photothermal interferometry systems.
• To demonstrate enhanced performance in sensitivity and dynamic range.

Main Methods:

• Exploited photothermal-induced phase change in a gas-filled hollow-core photonic bandgap fibre.
• Utilized low-cost near-infrared semiconductor lasers.
• Integrated components into a fibre-based platform.

Main Results:

• Demonstrated an all-fibre acetylene gas sensor.
• Achieved a noise equivalent concentration of 2 parts-per-billion (p.p.b.).
• Exhibited an unprecedented dynamic range of nearly six orders of magnitude.

Conclusions:

• Photothermal interferometry can be realized in an all-fibre format.
• This technology enables compact, ultra-sensitive, and selective optical sensors.
• The system is applicable to harsh environments and supports remote, multiplexed, and distributed sensing.