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

Jin W, Cao Y, Yang F, Ho HL - Nat Commun (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Electrical Engineering and Photonics Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China [2] Photonic Sensors Research Center, The Hong Kong Polytechnic University Shenzhen Research Institute, No. 18 Yuexing 1st Road, Nanshan District, Shenzhen 518057, China.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Second harmonic signal as function of gas concentration.(a) Second harmonic lock-in output signal when pump laser is tuned across the P(9) line of acetylene at 1,530.371 nm for 50, 100, 200, 400 p.p.m. acetylene concentration. (b) Second harmonic signal (peak-to-peak value) as function of gas concentration. Error bars in the horizontal axis are based on the accuracy of the two mass flow controllers we used to prepare different gas concentrations. Error bars in the vertical axis show the s.d. from five measurements and the magnitudes of the error bars are scaled up by 10-fold for clarity reason. The pump power in the hollow-core was estimated to be ∼25 mW and the mean probe power level on PD2 is ∼200 μW. The time constant of the lock-in amplifier is 1 s with a filter slope of 18 dB Oct−1, corresponding to a detection bandwidth of 0.094 Hz. The length of the sensing HC-PBF is 0.62 m.
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f4: Second harmonic signal as function of gas concentration.(a) Second harmonic lock-in output signal when pump laser is tuned across the P(9) line of acetylene at 1,530.371 nm for 50, 100, 200, 400 p.p.m. acetylene concentration. (b) Second harmonic signal (peak-to-peak value) as function of gas concentration. Error bars in the horizontal axis are based on the accuracy of the two mass flow controllers we used to prepare different gas concentrations. Error bars in the vertical axis show the s.d. from five measurements and the magnitudes of the error bars are scaled up by 10-fold for clarity reason. The pump power in the hollow-core was estimated to be ∼25 mW and the mean probe power level on PD2 is ∼200 μW. The time constant of the lock-in amplifier is 1 s with a filter slope of 18 dB Oct−1, corresponding to a detection bandwidth of 0.094 Hz. The length of the sensing HC-PBF is 0.62 m.

Mentions: The dynamic range of the HC-PBF-based PT spectroscopic system was tested with a 0.62-m-long HC-PBF. The experimental set-up used is slightly different from Fig. 2 (see Supplementary Fig. 2). The HC-PBF was spliced to SMF-pigtails while multiple microchannels were drilled into the hollow core of the HC-PBF (see Methods) for easy filling of the hollow core with different gas concentrations without the need for pressurization. Figure 4 shows the second harmonic lock-in output for acetylene concentration from ∼50 p.p.m. to ∼6% acetylene balanced with nitrogen. The lower acetylene concentrations (that is, 50 to 794 p.p.m.) were prepared by mixing pure nitrogen with 1% acetylene, while the higher concentrations were prepared by mixing nitrogen with 99.99% acetylene. An approximately linear relationship is obtained for acetylene concentration up to ∼1.6% and non-linearity starts to appear beyond this value. The lower detection limit in terms of 1σ NEC is estimated to be 30 p.p.b. (3.5 × 10−8 cm−1 in terms of NEA), giving a dynamic range of nearly six orders of magnitude (5.3 × 105). Such a high performance has not been achieved with any fibre-based gas detection system reported previously.


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

Jin W, Cao Y, Yang F, Ho HL - Nat Commun (2015)

Second harmonic signal as function of gas concentration.(a) Second harmonic lock-in output signal when pump laser is tuned across the P(9) line of acetylene at 1,530.371 nm for 50, 100, 200, 400 p.p.m. acetylene concentration. (b) Second harmonic signal (peak-to-peak value) as function of gas concentration. Error bars in the horizontal axis are based on the accuracy of the two mass flow controllers we used to prepare different gas concentrations. Error bars in the vertical axis show the s.d. from five measurements and the magnitudes of the error bars are scaled up by 10-fold for clarity reason. The pump power in the hollow-core was estimated to be ∼25 mW and the mean probe power level on PD2 is ∼200 μW. The time constant of the lock-in amplifier is 1 s with a filter slope of 18 dB Oct−1, corresponding to a detection bandwidth of 0.094 Hz. The length of the sensing HC-PBF is 0.62 m.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403440&req=5

f4: Second harmonic signal as function of gas concentration.(a) Second harmonic lock-in output signal when pump laser is tuned across the P(9) line of acetylene at 1,530.371 nm for 50, 100, 200, 400 p.p.m. acetylene concentration. (b) Second harmonic signal (peak-to-peak value) as function of gas concentration. Error bars in the horizontal axis are based on the accuracy of the two mass flow controllers we used to prepare different gas concentrations. Error bars in the vertical axis show the s.d. from five measurements and the magnitudes of the error bars are scaled up by 10-fold for clarity reason. The pump power in the hollow-core was estimated to be ∼25 mW and the mean probe power level on PD2 is ∼200 μW. The time constant of the lock-in amplifier is 1 s with a filter slope of 18 dB Oct−1, corresponding to a detection bandwidth of 0.094 Hz. The length of the sensing HC-PBF is 0.62 m.
Mentions: The dynamic range of the HC-PBF-based PT spectroscopic system was tested with a 0.62-m-long HC-PBF. The experimental set-up used is slightly different from Fig. 2 (see Supplementary Fig. 2). The HC-PBF was spliced to SMF-pigtails while multiple microchannels were drilled into the hollow core of the HC-PBF (see Methods) for easy filling of the hollow core with different gas concentrations without the need for pressurization. Figure 4 shows the second harmonic lock-in output for acetylene concentration from ∼50 p.p.m. to ∼6% acetylene balanced with nitrogen. The lower acetylene concentrations (that is, 50 to 794 p.p.m.) were prepared by mixing pure nitrogen with 1% acetylene, while the higher concentrations were prepared by mixing nitrogen with 99.99% acetylene. An approximately linear relationship is obtained for acetylene concentration up to ∼1.6% and non-linearity starts to appear beyond this value. The lower detection limit in terms of 1σ NEC is estimated to be 30 p.p.b. (3.5 × 10−8 cm−1 in terms of NEA), giving a dynamic range of nearly six orders of magnitude (5.3 × 105). Such a high performance has not been achieved with any fibre-based gas detection system reported previously.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Electrical Engineering and Photonics Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China [2] Photonic Sensors Research Center, The Hong Kong Polytechnic University Shenzhen Research Institute, No. 18 Yuexing 1st Road, Nanshan District, Shenzhen 518057, China.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus