Photothermal Gas Detection With a Dithered Low-Finesse Fiber-Optic Fabry-Pérot Interferometer

Flexible Hollow Core Fiber Photoacoustic Gas Sensor Based on Embedded Acoustic Resonant Structure

“…This is because the acoustic wave would suffer a lot from the gas viscous damping within a capillary tube (inner diameter at μm level or even smaller), such as anti-resonance hollow core fibers (AR-HCFs) and hollow core band gap fibers (HC-BPFs). Despite that these HCFs have been extensively used in photothermal (PT) gas sensors, , they have not been used in a PA gas sensor due to the ultrasmall inner diameter. The LHCFs own an inner diameter from 1 to 4 mm, which is exactly between the traditional metallic PA cells and the capillary tube-based hollow core fibers.…”

Gas Sensing System Based on an All-Fiber Photothermal Microcell

“…This causes atomic or molecular excitation and subsequent conversion to heat after collisional relaxation. Consequently, variations in the refractive index of the gas are produced within the gas cell, which can be detected using well-known interferometric principles based on Mach-Zehnder [6] or Fabry-Perot [7][8][9][10][11] interferometers. Periodic excitation of the gas allows the use of phase-sensitive detection techniques [9,10], which can improve the signal-to-noise ratio (SNR) significantly, and, thus, the sensor's detection limit.…”

“…Consequently, variations in the refractive index of the gas are produced within the gas cell, which can be detected using well-known interferometric principles based on Mach-Zehnder [6] or Fabry-Perot [7][8][9][10][11] interferometers. Periodic excitation of the gas allows the use of phase-sensitive detection techniques [9,10], which can improve the signal-to-noise ratio (SNR) significantly, and, thus, the sensor's detection limit. Conventional photothermal spectroscopy setups typically utilize free-space optical components to form high-finesse Fabry-Perot interferometers [12].…”

“…Various designs of all-fiber photothermal gas sensors were proposed to mitigate these limitations [15]. These designs were based mainly on hollow core/photonic crystal fibers (HC/PCF) [10,[15][16][17][18][19][20], which allow for easy alignment and guidance of the excitation and probe beam over longer distances, thus decreasing the detection limits (down to the ppb range). At the same time, high excitation frequencies can be applied (10 kHz [10], 50 kHz [15], 2.7 kHz [16], 12.5 kHz [17], etc.).…”

“…These designs were based mainly on hollow core/photonic crystal fibers (HC/PCF) [10,[15][16][17][18][19][20], which allow for easy alignment and guidance of the excitation and probe beam over longer distances, thus decreasing the detection limits (down to the ppb range). At the same time, high excitation frequencies can be applied (10 kHz [10], 50 kHz [15], 2.7 kHz [16], 12.5 kHz [17], etc.). Nevertheless, the hollow core fiber approach also has significant limitations, like impaired gas exchange among the surrounding and the hollow core gas, which is usually achieved through small side openings [15], leading to long system response times (for example, 40 s in [15], 63 s in [16], 52 s in [18] and 19 s in [19]).…”