High Sensitivity Heterodyne Electro-Optic Sampling with 1.5-µm Laser Source

AbstractDevelopment of novel mid-infrared (MIR) lasers could ultimately boost emerging detection technologies towards innovative spectroscopic and imaging solutions. Photoacoustic (PA) modality has been heralded for years as one of the most powerful detection tools enabling high signal-to-noise ratio analysis. Here, we demonstrate a novel, compact and sensitive MIR-PA system for carbon dioxide (CO2) monitoring at its strongest absorption band by combining a gas-filled fiber laser and PA technology. Specifically, the PA signals were excited by a custom-made hydrogen (H2) based MIR Raman fiber laser source with a pulse energy of ⁓ 18 μJ, quantum efficiency of ⁓ 80% and peak power of ⁓ 3.9 kW. A CO2 detection limit of 605 ppbv was attained from the Allan deviation. This work constitutes an alternative method for advanced high-sensitivity gas detection.

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Defects Detection and Localization in Underwater Plates Using Laser Laterally Generated Pure Non-Dispersive S0 Mode

Applied Sciences ◽

10.3390/app9030459 ◽

2019 ◽

Vol 9 (3) ◽

pp. 459 ◽

Cited By ~ 2

Author(s):

Qingnan Xie ◽

Chenyin Ni ◽

Zhonghua Shen

Keyword(s):

Defect Detection ◽

Lamb Waves ◽

Mode Conversion ◽

High Sensitivity ◽

Laser Source ◽

Dispersion Characteristics ◽

High Attenuation ◽

Corrosion Defects ◽

Detection And Localization ◽

Lateral Excitation

When working in humid environments, corrosion defects are easily produced in metallic plates. For defect detection in underwater plates, symmetric modes of Lamb waves are widely used because of their characteristics including long propagating distance and high sensitivity to defects. In this study, we extend our previous work by applying the laser laterally generated S0 mode to detection and localization of defects represented by artificial notches in an aluminum plate immersed in water. Pure non-dispersive S0 mode is generated in an underwater plate by lateral laser source irradiation and its fd (frequency·thickness) range is selected by theoretical calculation. Using this lateral excitation, the S0 mode is enhanced; meanwhile, the A0 mode is effectively suppressed. The mode-converted A0 mode from the incident S0 mode is used to detect and localize the defect. The results reveal a significantly improved capability to detect defects in an underwater plate using the laser laterally generated S0 mode, while that using A0 is limited due to its high attenuation. Furthermore, owing to the long propagating distance and the non-dispersion characteristics of the S0 generated by the lateral laser source, multiple defects can also be detected and localized according to the mode conversion at the defects.

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The Application of Signal Processing Techniques in Improving Spectrometer Detection Limit

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.148-149.1045 ◽

2011 ◽

Vol 148-149 ◽

pp. 1045-1050

Author(s):

Zhi Ying Wu ◽

Yi Zhang ◽

Zuo Yuan Shen

Keyword(s):

Signal Processing ◽

Detection Limit ◽

High Sensitivity ◽

Processing Technique ◽

Laser Source ◽

Sampled Data ◽

High Concentration ◽

Signal Processing Technique ◽

Processing Techniques ◽

Lock In

Improving spectrometer detection limit using statistical principle and signal-processing technique are described simply in this work. In the detection of gas photoacoustic(PA) signal, accurate partitions of the sampled data affect on the detection limit to some extent although Lock-in amplification technique with high SNR and microphone sensor with high sensitivity have been used. A model and the resulting algorithm are proposed from PA-signal samples. The techniques are validated at ppb level on PA spectrometer for NH3 breath detection in high concentration of CO2 and H2O based on tunable erbium-doped fiber laser (TEDFL) or for multicomponent trace gas detection based on waveguide CO2 laser or on other laser source.

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